• 146. Formulating Electron Beam-Induced Covalent Linkages for Stable and High-Energy-Density Silicon Microparticle Anode Advanced Science, 2305298 (2024)

    Minjun Je, Hye Bin Son, Yu-Jin Han, Hangeol Jang, Sungho Kim, Dongjoo kim, Jieun Kang, Jin-Hyeok Jeong, Chihyun Hwang, Gyujin Song, Hyun-Kon Song, Tae Sung Ha, Soojin Park*

    High-capacity silicon (Si) materials hold a position at the forefront of advanced lithium-ion batteries. The inherent potential offers considerable advantages for substantially increasing the energy density in batteries, capable of maximizing the benefit by changing the paradigm from nano- to micron-sized Si particles. Nevertheless, intrinsic structural instability remains a significant barrier to its practical application, especially for larger Si particles. Here, a covalently interconnected system is reported employing Si microparticles (5 µm) and a highly elastic gel polymer electrolyte (GPE) through electron beam irradiation. The integrated system mitigates the substantial volumetric expansion of pure Si, enhancing overall stability, while accelerating charge carrier kinetics due to the high ionic conductivity. Through the cost-effective but practical approach of electron beam technology, the resulting 500 mAh-pouch cell showed exceptional stability and high gravimetric/volumetric energy densities of 413 Wh kg−1, 1022 Wh L−1, highlighting the feasibility even in current battery production lines.

  • 145. Double Activation of Water Splitting by Strong Cation–Water Interaction J. Phys. Chem. C, 127(42), 20718-20726 (2023)

    Do Sol Cheong, Jisu Lee, Jiyun Lee, Kyung Min Lee, Yeongdae Lee, Sang Kyu Kwak*, Dong-Gyu Lee*, and Hyun-Kon Song*

    Presented herein is the possibility of activating water molecules associatively by cations in electrolytes, as well as active sites of electrocatalysts. Cation–water interaction (CW), weakening the intramolecular O–H bonds of water molecules, significantly affected dissociation of water molecules in proton-deficient media, resulting in hydrogen evolution reaction (HER) based on water reduction reaction (WRR). Both the quantitative and qualitative hydration nature of cations (i.e., hydration strength and number) determined the strength of CW and therefore the WRR activity. The cationic dependency of CW on electrolytes was confirmed by bulk and surface-specific spectroscopic techniques. After the cation–water complexes based on strong CW (cation(water)n) were defined as the main reactants for WRR, the intermediate adsorbate on the catalyst surface was suggested to be water molecules doubly coordinated to cations as well as active sites (cation-water-catalyst). The double activation picture of the tricomponent intermediate was strongly supported by the surface-specific Raman spectra, confirming the polarization-induced weakening of the O–H bonds of water molecules near the Pt catalyst surface in addition to the CW-induced O–H weakening found in the electrolyte as well as on the catalyst surface. The smallest divalent Be2+ among a series of test cations, including the monovalent, divalent, and trivalent ones, showed the most remarkable WRR kinetic gain, the superiority of which was expected from its high charge density nature guaranteeing strong hydration strength and cationic acidity. The beryllium anomaly to eminently weaken the O–H bonds accelerated WRR at pH2 with 600 mV overpotential gain for 150 mA cm–2 hydrogen production (c.f., 28 mA cm–2 with Na+).

  • 144. Guaiacol as an Organic Superoxide Dismutase Mimics for Anti-ageing a Ru-based Li-rich Layered Oxide Cathode Angew. Chem. Int. Ed, e202312928 (2023)

    Jeongin Lee, Min-Ho Kim, Hosik Lee, Jonghak Kim, Jeongwoo Seo, Hyun-Wook Lee*, Chihyun Hwang*, and Hyun-Kon Song*

    High-capacity Li-rich layered oxides using oxygen redox as well as transition metal redox suffer from its structural instability due to lattice oxygen escaped from its structure during oxygen redox and the following electrolyte decomposition by the reactive oxygen species. Herein, we rescued a Li-rich layered oxide based on 4d transition metal by employing an organic superoxide dismutase mimics as a homogeneous electrolyte additive. Guaiacol scavenged superoxide radicals via dismutation or disproportionation to convert two superoxide molecules to peroxide and dioxygen after absorbing lithium superoxide on its partially negative oxygen of methoxy and hydroxyl groups. Additionally, guaiacol was decomposed to form a thin and stable cathode-electrolyte interphase (CEI) layer, endowing the cathode with the interfacial stability.

  • 143. Fire-Inhibiting Nonflammable Gel Polymer Electrolyte for Lithium-Ion Batteries ACS Energy Letters, 8(11), 4650-4657 (2023)

    Jihong Jeong, Mideum Kim, Hyeju Shin, Hosik Lee, Yoon-Gyo Cho, Minjae Cho, Jisu Lee, Cheolhee Han, Gunyoung Kim, Hongkyung Lee, Hochun Lee, Tae-Hee Kim*, Seo-Hyun Jung*, and Hyun-Kon Song*

    Herein, we present a gel polymer electrolyte (GPE) improving nonflammability of lithium-ion batteries (LIBs) by blocking radical-initiated chain reactions which cause thermal runaway and finally fire issues. The polymer that makes up the nonflammable GPE was (1) soluble in carbonate electrolytes, (2) cross-linkable in the presence of a popularly used lithium salt such as LiPF6, (3) gelated only with 2 wt % in electrolytes, and (4) radical-scavenging by its functional side chains. Electrolytes having the polymer were thermally gelated within battery cells after the cells were assembled by a conventional way. LIB cells with the GPE were durable against external thermal and mechanical shocks without sacrificing cell performances. The high transference number of lithium ions and liquid-equivalent ionic conductivity of the GPE at only 2% solid content having a stable solid-electrolyte interphase layer formed even improved cell performances at normal operation conditions.

  • 142. Influence of the Lithium-Ion Concentration in Electrolytes on the Performance of Dye-Sensitized Photorechargeable Batteries ACS Applied Materials & Interfaces 15(34), 40378–40384 (2023)

    Hyun-Gyu Han, So Yeon Yoon, Byung-Man Kim, Myeong-Hee Lee, Sungtae Kim, HyeonOh Shin, Deok-Ho Roh, Hyun-Kon Song*, and Tae-Hyuk Kwon*

    Dye-sensitized photorechargeable batteries (DSPBs) have recently gained attention for realizing energy recycling systems under dim light conditions. However, their performance under high storage efficiency (i.e., the capacity charged within a limited time) for practical application remains to be evaluated. Herein, we varied the lithium (Li)-ion concentration, which plays a dual role as energy charging and storage components, to obtain the optimized energy density of DSPBs. Electrochemical studies showed that the Li-ion concentration strongly affected the resistance characteristics of DSPBs. In particular, increasing the Li-ion concentration improved the output capacity and decreased the output voltage. Consequently, the energy density of the finely optimized DSPB improved from 8.73 to 12.64 mWh/cm3 when irradiated by a 1000-lx indoor light-emitting-diode lamp. These findings on the effects of Li-ion concentrations in electrolytes on the performance of DSPBs represent a step forward in realizing the practical application of DSPBs.

  • 141. Low-Voltage Hydrogen Production via Hydrogen Peroxide Oxidation Facilitated by Oxo Ligand Axially Coordinated to Cobalt in Phthalocyanine Moiety Small, 2303263 (2023)

    Jisu Lee, Boreum Lee, Yeongdae Lee, Ahyeon Kim, Dong-gyu Lee*, Hankwon Lim*, Hyun-Kon Song*

    A cobalt phthalocyanine having an electron-poor CoN4 (+δ) in its phthalocyanine moiety was presented as an electrocatalyst for hydrogen peroxide oxidation reaction (HPOR). We suggested that hydrogen peroxide as an electrolysis medium for hydrogen production and therefore as a hydrogen carrier, demonstrating that the electrocatalyst guaranteed high hydrogen production rate by hydrogen peroxide splitting. The electron deficiency of cobalt allows CoN4 to have the highly HPOR-active monovalent oxidation state and facilitates HPOR at small overpotentials range around the onset potential. The strong interaction between the electron-deficient cobalt and oxygen of peroxide adsorbates in Co─OOH encourages an axially coordinated cobalt oxo complex (O═CoN4) to form, the O═CoN4 facilitating the HPOR efficiently at high overpotentials. Low-voltage oxygen evolution reaction guaranteeing low-voltage hydrogen production is successfully demonstrated in the presence of the metal–oxo complex having electron-deficient CoN4. Hydrogen production by 391 mA cm−2 at 1 V and 870 mA cm−2 at 1.5 V is obtained. Also, the techno-economic benefit of hydrogen peroxide as a hydrogen carrier is evaluated by comparing hydrogen peroxide with other hydrogen carriers such as ammonia and liquid organic hydrogen carriers.

  • 140. Full-Hexacyanometallate Aqueous Redox Flow Batteries Exceeding 1.5 V in an Aqueous Solution Advanced Energy Materials, 2300707 (2023)

    Ji-Eun Jang, Ryeong-ah Kim, S. Jayasubramaniyan, Chanhee Lee, Jieun Choi, Youngdae Lee, Sujin Kang, Jaechan Ryu, Seok Woo Lee, Jaephil Cho, Dong Woog Lee, Hyun-Kon Song, Wonyoung Choe, Dong-Hwa Seo,* and Hyun-Wook Lee*

    Aqueous redox flow batteries (RFBs) have attracted significant attention as energy storage systems by virtue of their inexpensive nature and long-lasting features. Although all-vanadium RFBs exhibit long lifetimes, the cost of vanadium resources fluctuates considerably, and is generally expensive. Iron–chromium RFBs take advantage of utilizing a low-cost and large abundance of iron and chromite ore; however, the redox chemistry of CrII/III generally involves strong Jahn–Teller effects. Herein, this work introduces a new Cr-based negolyte coordinated with strong-field ligands capable of mitigating strong Jahn–Teller effects, thereby facilitating low redox potential, high stability, and rapid kinetics. The balanced full-cell configuration features a stable lifetime of 500 cycles with energy density of 14 Wh L−1. With an excessive posolyte, the full-cell can attain a high energy density of 38.6 Wh L−1 as a single electron redox process. Consequently, the proposed system opens new avenues for the development of high-performance RFBs.

  • 139. Copper with an atomic-scale spacing for efficient electrocatalytic co-reduction of carbon dioxide and nitrate to urea Energy & Environmental Science 16, 2003-2013 (2023)

    Seokmin Shin, Siraj Sultan, Zong-Xian Chen, Hojeong Lee, Hansaem Choi, Tae-Ung Wi, Changhyun Park, Tae Won Kim, Chanhee Lee, Jihong Jeong, Hyeju Shin, Tae-Hee Kim, Hyungkuk Ju,Hyung-Chul Yoon, Hyun-Kon Song*, Hyun-Wook Lee*, Mu-Jeng Cheng* and Youngkook Kwon*

    The electrochemical co-reduction of carbon dioxide (CO2) and nitrate (NO3-) to urea via C-N bond coupling is a promising alternative to traditional industrial processes that are intensive in energy consumption and CO2 emission. However, due to the lack of suitable catalysts, the electrochemical process for urea synthesis suffers from low Faradaic efficiency, current density, and product yield, which highlights the importance of developing new catalysts that work efficiently for the co-reduction of CO2 and nitrate NO3- (CR-CO2/NO3-) and the corresponding C-N bond coupling reactions. Here, we report that the copper (Cu) with atomic-scale spacings (ds) between copper facets can significantly improve the electrochemical synthesis of urea from CR-CO2/NO3-. We used the lithiation approach to create ds between the copper facets. We prepared four Cu samples with different ds values simply by controlling the degree of lithiation on each sample. Among four samples, the Cu with ds close to 6 Å achieves a remarkably high urea yield rate of 7,541.9 μg h-1 mgcat-1 and partial current density of 115.25 mA cm−2, substantially greater than the bare Cu (urea yield rate of only 444.7 μg h-1 mgcat-1 and urea partial current density of 1.96 mA cm−2) counterpart. Our density functional theory calculations suggest that compared with bare Cu, the Cu with ds of 6.0 Å significantly lowers the energy barrier for C-N coupling, enhancing the C-N bond formation kinetically and thermodynamically, therefore leading to much-improved urea formation from CR-CO2/NO3-.

  • 138. Selectively Enhanced Electrocatalytic Oxygen Evolution within Nanoscopic Channels Fitting a Specific Reaction Intermediate for Seawater Splitting Small 2206918, (2022)

    Seokmin Shin, Tae-Ung Wi, Tae-Hoon Kong, Chanhyun Park, Hojeong Lee, Jihong Jeong, Eunryeol Lee, Subhin Yoon, Tae-Hee Kim Hyun-Wook Lee*, Youngkook Kwon*, and Hyun-Kon Song*

    Abundant availability of seawater grants economic and resource-rich benefits to water electrolysis technology requiring high-purity water if undesired reactions such as chlorine evolution reaction (CER) competitive to oxygen evolution reaction (OER) are suppressed. Inspired by a conceptual computational work suggesting that OER is kinetically improved via a double activation within 7 Å-gap nanochannels, RuO2 catalysts are realized to have nanoscopic channels at 7, 11, and 14 Å gap in average (dgap), and preferential activity improvement of OER over CER in seawater by using nanochanneled RuO2 is demonstrated. When the channels are developed to have 7 Å gap, the OER current is maximized with the overpotential required for triggering OER minimized. The gap value guaranteeing the highest OER activity is identical to the value expected from the computational work. The improved OER activity significantly increases the selectivity of OER over CER in seawater since the double activation by the 7 Å-nanoconfined environments to allow an OER intermediate (*OOH) to be doubly anchored to Ru and O active sites does not work on the CER intermediate (*Cl). Successful operation of direct seawater electrolysis with improved hydrogen production is demonstrated by employing the 7 Å-nanochanneled RuO2 as the OER electrocatalyst.

  • 137. Very strong interaction between FeN4 and titanium carbide for durable 4-electron oxygen reduction reaction suppressing catalyst deactivation by peroxide Journal of Materials Chemistry A 10, 24041-24050 (2022)

    Yeongdae Lee, Jang Hyuk Ahn, Haeseong Jang, Jisu Lee, Subhin Yoon, Dong-Gyu Lee, Min Gyu Kim,* Jun Hee Lee* and Hyun-Kon Song*

    Catalyst-support interaction triggering biased electron flows between catalyst and reactant has been studied for electrocatalysis. The interaction was limited to the interfacial region between catalyst and support when nanoparticular catalysts, which are bulky from the viewpoint of atomic dimension, were employed. To clarify and maximize the effects of supports, herein, we investigated the catalyst-support interaction of a molecular catalyst loaded on a support. Iron phthalocyanine (FePc) as the molecular catalyst for oxygen reduction reaction (ORR) was loaded on two-dimensional monolayer leaf of titanium carbide (1L-Ti3C2). The strong interaction between Fe of FePc and Ti of 1L-Ti3C2 developed via FeTi2 coordination encouraged the square planar structure of FePc to be concavely distorted. The electron-rich Fe active site having extra electrons given by less electronegative Ti of Ti3C2 allowed the single oxygen intermediate species (*O) readily protonated to be *OH, moving the RDS to the desorption step having a lower free energy uphill or kinetic barrier. Resultantly, the strong FePc-Ti3C2 interaction decreased the potential required for reducing oxygen and moreover completed ORR via four-electron (4e) process rather than 2e ORR. The catalyst durability was also improved due to the absence of peroxide generated from the 2e process.

  • 136. Amphi-Active Superoxide-Solvating Charge Redox Mediator for Highly Stable Lithium–Oxygen Batteries ACS Applied Materials & Interfaces 14, 40793–40800 (2022)

    Jonghak Kim, Jinhyeon Jeong, Gwan Yeong Jung, Jeongin Lee, Ji Eun Lee, Kyungeun Baek, Seok Ju Kang, SangKyu Kwak*, Chihyun Hwang*, and Hyun-Kon Song*

    A multifunctional electrolyte additive for lithium oxygen batteries (LOBs) was designed to have (1) a redox-active moiety to mediate decomposition of lithium peroxide (Li2O2 as the final discharge product) during charging and (2) a solvent moiety to solvate and stabilize lithium superoxide (LiO2 as the intermediate discharge product) in electrolyte during discharging. 4-Acetamido-TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidin-1-yl)oxyl) or AAT was employed as the additive working for both charge and discharge processes (amphi-active). The redox-active moiety was rooted in TEMPO, while the acetamido (AA) functional group inherited the high donor number (DN) of N,N-dimethylacetamide (DMAc). Integrating two functional moieties (TEMPO and AA) into a single molecule resulted in the bifunctionality of AAT (1) facilitating Li2O2 decomposition by the TEMPO moiety and (2) encouraging the solvent mechanism of Li2O2 formation by the high-DN AA moiety. Significantly improved LOB performances were achieved by the superoxide-solvating charge redox mediator, which were not obtained by a simple cocktail of TEMPO and DMAc.

  • 135. In situ gel electrolyte network guaranteeing ionic communication between solid electrolyte and cathode Journal of Power Sources 546, 231926 (2022)

    Hyeju Shin, Seong Jin Choi, Sinho Choi, Bo Yun Jang, Jihong Jeong, Yoon-Gyo Cho, Sang-Young Lee, Hyun-Kon Song, Ji Haeng Yu*, Tae-Hee Kim*

    Solid electrolytes are regarded as promising candidates replacing organic liquid electrolyte due to much enhanced safety, which is able to use lithium metal as an anode material for high energy system. Among several solid electroytes, garnet-type solid electrolyte has wide electrochemical window as well as high chemical stability and ionic conductivity at room temperature. However, from an assembled full cell's point of view, high interfacial resistance between electrode and solid electrolyte is a huge obstacle which should be overcome. Herein, we synthesize high ionic conductivy of Gallium-doped garnet-type solid electrolyte (Li6.25Ga0.25La3Zr2O12) having 1.2 mS cm-1 at room temperature and then applied gel polymer electrolyte into cathode by in situ gelation method for a full cell system. The interfacial resistance is reduced by about 260 times and rate capability from 0.05C to 1C was 80%, which is superior to a hybrid of liquid electrolyte and LGLZO cell system. Initial capacity retaines 89% even after 800 cycles at 0.5C.

  • 134. Molecularly Engineered Carbon Platform To Anchor Edge-Hosted Single-Atomic M–N/C (M = Fe, Co, Ni, Cu) Electrocatalysts of Outstanding Durability ACS Catalysis 12, 7994-8006 (2022)

    Woo Yeong Noh, Jinhong Mun, Yeongdae Lee, Eun Mi Kim, Young Kyeong Kim, Kwang Young Kim, Hu Young Jeong, JongHoon Lee, Hyun-Kon Song*, Geunsik Lee*, and Jae Sung Lee*

    A powerful synthetic protocol based on a molecularly engineered anchoring carbon platform (ACP) is reported to stabilize concentrated edge-hosted single-atom catalytic sites of M–N (M = Fe, Co, Ni, Cu) on carbon supports. Polymerization with l-cysteine as an additional organic precursor produces an ACP sheath around the carbon nanotube (CNT)–graphene (GR) hybrid support made of a small domain size with abundant edge sites and doped with sulfur. A few-minute-long microwave pyrolysis anchors strongly the single-atomic M–N moiety on the ACP while suppressing its agglomeration during the high-temperature synthesis and makes the ACP highly graphitized. As a typical example, the edge-hosted single-atomic catalytic sites in Fe–N/S-CNT–GR provide superior pH-independent oxygen reduction reaction (ORR) activity to previously reported Fe–N–C catalysts and commercial Pt/C while demonstrating oxygen evolution reaction (OER) activity in basic conditions similar to known state-of-the-art catalysts. In particular, the Fe–N/S-CNT–GR catalyst is much more stable than commercial Pt/C and Ir/C catalysts during ORR and OER in both base and acid solutions. Inferior stability is a common problem of this type of single-atom heterogeneous catalyst (SAC). An aqueous Zn–air battery with our Fe–N/S-CNT–GR catalyst operates as effectively as the device with the commercial Pt/C–Ir/C catalysts. We believe that our protocol based on the molecularly engineered ACP and microwave pyrolysis can provide a new concept to synthesize a new generation of durable SACs, which could have broad applications in electrochemical energy conversion and storage.

  • 133. Shifting Target Reaction from Oxygen Reduction to Superoxide Disproportionation by Tuning Isomeric Configuration of Quinone Derivative as Redox Mediator for Lithium–Oxygen Batteries ACS Applied Materials & Interfaces 14, 9066-9072 (2022)

    Jonghak Kim, Jeongin Lee, Jinhyeon Jeong, Chihyun Hwang*, and Hyun-Kon Song*

    Quinones having a fully conjugated cyclic dione structure have been used as redox mediators in electrochemistry. 2,5-Ditert-butyl-1,4-benzoquinone (DBBQ or DB-p-BQ) as a para-quinone derivative is one of the representative discharge redox mediators for facilitating the oxygen reduction reaction (ORR) kinetics in lithium–oxygen batteries (LOBs). Herein, we presented that the redox activity of DB-p-BQ for electron mediation was possibly used for facilitating superoxide disproportionation reaction (SODR) by tuning the isomeric configuration of the carbonyl groups of the substituted quinone to change its reduction potentials. First, we expected a molecule having its reduction potential between oxygen/superoxide at 2.75 V versus Li/Li+ and superoxide/peroxide at 3.17 V to play a role of the SODR catalyst by transferring an electron from one superoxide (O2–) to another superoxide to generate dioxygen (O2) and peroxide (O22–). By changing the isomeric configuration from para (DB-p-BQ) to ortho (DB-o-BQ), the reduction potential of the first electron transfer (Q/Q–) of the ditert-butyl benzoquinone shifted positively to the potential range of the SODR catalyst. The electrocatalytic SODR-promoting functionality of DB-o-BQ kept the reactive superoxide concentration below a harmful level to suppress superoxide-triggered side reaction, improving the cycling durability of LOBs, which was not achieved by the para form. The second electron transfer process (Q–/ Q2–) of the DB-o-BQ, even if the same process of the para form was not used for facilitating ORR, played a role of mediating electrons between electrode and oxygen like the Q/Q– process of the para form. The ORR-promoting functionality of the ortho form increased the LOB discharge capacity and reduced the ORR overpotential.

  • 132. Argentophilic pyridinic nitrogen for embedding lithiophilic silver nanoparticles in a three-dimensional carbon scaffold for reversible lithium plating/stripping Journal of Materials Chemistry A 10, 1768–1779 (2022)

    Yuju Jeon, Jonghak Kim, Haeseong Jang, Jeongin Lee, Min Gyu Kim, Nian Liu* and Hyun-Kon Song*

    Reversible lithium metal plating and stripping are required for the durable operation of lithium metal batteries. Three-dimensional architecture has been employed for accommodating volume change of lithium metal during repeated plating and stripping while lithiophilic materials have been utilized for the even plating of lithium metal. One of the best pictures would be a three-dimensional electrically conductive scaffold having a significant amount of lithiophilic sites homogenously distributed on its skeleton. To realize the ideal architecture for lithium metal anodes, herein, we embedded silver nanoparticles as lithiophile in a three-dimensional carbon scaffold. To overcome the limited loading amount of silver in the porous structure, melamine as an argentophile having argentophilic (silver-philic) pyridinic nitrogen was introduced into the carbon scaffold. Melamine as the argentophile increased the silver loading ten times in the three-dimensional scaffold via the strong interaction with silver cation. The heavy lithiophile (silver) loading increased the lithium storage capacity, guaranteeing uniform lithium distribution throughout the scaffold. The silver nanoparticles loaded in the scaffold were alloyed with lithium to be silver–lithium alloy (AgxLiy) during lithium metal plating. The alloy served as the lithiophilic nucleation sites for the dendrite-free growth of lithium metal. As a result, the strong lithiophilicity derived from the heavy-loading silver improved the reversibility of lithium plating and stripping. The cycling durability of lithium metal batteries with lithium-ion-battery cathode reaction and oxygen reduction reaction was twice improved by employing the lithium-metal-infused 3D scaffold anode having the highest lithiophile loading with internal space enough to accommodate the volume of lithium metal.

  • 131. Critical Void Dimension of Carbon Frameworks to Accommodate Insoluble Products of Lithium-Oxygen Batteries ACS Applied Materials & Interfaces 14, 492–501 (2022)

    Chihyun Hwang, Myung-Jun Kwak, Jinhyeon Jeong, Kyungen Baek, Ki-Yong Yoon, Cheolwon An, Jin-Wook Min, Jonghak Kim, Jeongin Lee, Seok ju Kang, Ji-Hyuen Jang*, and Hyun-kon Song*

    High-energy density lithium–oxygen batteries (LOBs) seriously suffer from poor rate capability and cyclability due to the slow oxygen-related electrochemistry and uncontrollable formation of lithium peroxide (Li2O2) as an insoluble discharge product. In this work, we accommodated the discharge product in macro-scale voids of a carbon-framed architecture with meso-dimensional channels on the carbon frame and open holes connecting the neighboring voids. More importantly, we found that a specific dimension of the voids guaranteed high capacity and cycling durability of LOBs. The best LOB performances were achieved by employing the carbon-framed architecture having voids of 0.8 μm size as the cathode of the LOB when compared with the cathodes having voids of 0.3 and 1.4 μm size. The optimized void size of 0.8 μm allowed only a monolithic integrity of lithium peroxide deposit within a void during discharging. The deposit was grown to be a yarn ball-looking sphere exactly fitting the shape and size of the void. The good electric contact allowed the discharge product to be completely decomposed during charging. On the other hand, the void space was not fully utilized due to the mass transfer pathway blockage at the sub-optimized 0.3 μm and the formation of multiple deposit integrities within a void at the sur-optimized 1.4 μm. Consequently, the critical void dimension at 0.8 μm was superior to other dimensions in terms of the void space utilization efficiency and the lithium peroxide decomposition efficiency, disallowing empty space and side reactions during discharging.

  • 130. Malonic-acid-functionalized fullerene enables the interfacial stabilization of Ni-rich cathodes in lithium-ion batteries Journal of Power Sources 521, 230923 (2022)

    Chanhyun Park, Eunryeol Lee, Su Hwan Kim, Jung-Gu Han, Chihyun Hwang, Se Hun Joo, Kyungeun Baek, Seok Ju Kang, Sang Kyou Kwak*, Hyun-Kon Song*, and Nam-Soon Choi*

    High-capacity LiNi1-x-yCoxMnyO2 (NCM) (x + y ≤ 0.2) is a potential candidate for realizing high-energy-density lithium-ion batteries (LIBs). However, successful application of this cathode requires overcoming the irreversible phase transition (layered-to-spinel/rock-salt), interfacial instability caused by residual lithium compounds, and the electrolyte oxidation promoted by highly oxidized Ni4+. In this study, we investigate the roles of fullerene with malonic acid moieties (MA-C60) as a superoxide dismutase mimetic (SODm) electrolyte additive in LIBs to deactivate reactive radical species (O2•-, LiOCO3•, and Li(CO3)2•) induced by electrochemical oxidation of residual lithium compound, Li2CO3 on the LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode surface and to scavenge trace water to avoid undesirable hydrolysis of LiPF6. Further, MA-C60 maintains the structural stability of NCM811 cathodes and mitigates the parasitic reaction of residual lithium compounds with LiPF6 through the formation of a stable cathode–electrolyte interface. Our findings showed that MA-C60 helps overcome the challenges associated with Li2CO3 oxidation at the NCM811 cathode, which produces CO2 gas and O2•- that react with the solvent molecules

  • 129. Breathable Artificial Interphase for Dendrite-Free and Chemo-Resistive Lithium Metal Anode Small, 2105724 (2021)

    Gyujun Song, Chihyun Hwang, Woo-jin Song, Jung Hyun Lee, Sangyeop Lee, Dong-Yeob Han, Jonghak Kim, Hyesun g Park, Hyun-Kon Song*, and Soojin Park*

    A dendrite-free and chemically stabilized lithium metal anode is required for extending battery life and for the application of high energy density coupled with various cathode systems. However, uneven Li metal growth and the active surface in nature accelerate electrolyte dissipation and surface corrosion, resulting in poor cycle efficiency and various safety issues. Here, the authors suggest a thin artificial interphase using a multifunctional poly(styrene-b-butadiene-b-styrene) (SBS) copolymer to inhibit the electrochemical/chemical side reaction during cycling. Based on the physical features, hardness, adhesion, and flexibility, the optimized chemical structure of SBS facilitates durable mechanical strength and interphase integrity against repeated Li electrodeposition/dissolution. The effectiveness of the thin polymer film enables high cycle efficiency through the realization of a dendrite-free structure and a chemo-resistive surface of Li metal. The versatile anode demonstrates an improvement in the electrochemical properties, paired with diverse cathodes of high-capacity lithium cobalt oxide (3.5 mAh cm−2) and oxygen for advanced Li metal batteries with high energy density.

  • 128. Metal-nitrogen intimacy of the nitrogen-doped ruthenium oxide for facilitating electrochemical hydrogen production Applied Catalysis B: Environmental 303, 120873 (2022)

    Yeongdae Lee, Jang Hyuk Ahn, Seokmin Shin, Seo-Hyun Jung, Han-Saem Park, Yoon-Gyo Cho, Dong-Gyu Lee, Hoyoul Kong, JunHee Lee*, and Hyun-Kon Song*

    In order to realize electrochemically efficient hydrogen production, various endeavors have been devoted to developing hydrogen evolution reaction (HER) electrocatalysts having zero hydrogen binding energy (ΔGH* = 0) for balancing between adsorption and desorption. This work demonstrated that nitrogen doping improved the HER activity of ruthenium oxide by letting its ΔGH* approach zero or facilitating hydrogen desorption process. A highly nitrogen-doped ruthenium oxide catalyst guaranteeing the ruthenium-nitrogen intimacy was prepared by employing a polymer whose nitrogen-containing moiety (pyrrolidone) was strongly coordinated to ruthenium ion in the precursor solution prior to calcination. The less electronegative nature of nitrogen (when compared with oxygen) decreased the free energy uphill required for desorption of hydrogen intermediate species sitting on the nitrogen (H-*N to 1/2 H2 + *N) to make the desorption process more favored. Also, the nitrogen dopant facilitated OH- desorption from its neighboring ruthenium site (HO-*Ru + e- to HO- + *Ru) since the less electronegative nitrogen withdrew less electrons from the ruthenium site. The ruthenium-nitrogen intimacy of the catalyst more than doubled the electrocatalytic HER current from 33 mA cm-2 for an undoped RuO2 to 79 mA cm-2 for the nitrogen-doped RuO2 at -50 mVRHE.

  • 127. Breaking the Linear Scaling Relationship by a Proton Donor for Improving Electrocatalytic Oxygen Reduction Kinetics ACS Catalysis 11, 20, 12712-12720 (2021)

    Dong-Gyu Lee, Su Hwan Kim, Hyun Ho Lee, Seokmin Shin, Jiyun Lee, Se Hun Joo, Yeongdae Lee, Sang Kyu Kwak*, and Hyun-Kon Song*

    Theoretical computational studies have claimed that the catalytic activity of a family of heterogeneous catalysts (e.g., metal catalysts) is governed by a linear scaling relationship (LSR) between adsorption energy levels of intermediates on active sites of catalysts. The volcano shape of the activity versus the adsorption energy of one of the intermediates was obtained from the LSR and the Brønsted–Evans–Polanyi relationship. An improved activity can be achieved using a catalyst having optimized adsorption energy of the volcano or alternatively by circumventing or breaking the LSR. Herein, we demonstrated that the LSR of a series of transition metal terephthalates (MTPs; M = Fe, Co, Ni, Cu, or Zn) as electrocatalysts for the oxygen reduction reaction (ORR) was broken in the presence of polypyrrole (pPy) as a proton donor. The reason for the LSR breakage was that the intermediate to which the proton of pPy was delivered was different depending on the metal of MTP. Also, pPy affected the adsorption energy of the specific intermediate (the target of the proton transfer) more strongly while the other intermediates were less affected by pPy. Experimentally as well as theoretically, pPy significantly improved the ORR activity of MTPs, altering the activity volcano plot. The most significant improvement was found on CoTP: the onset potential of ORR on CoTP was shifted toward the more easy-to-be reduced direction from 0.7 to 0.85 VRHE at 1 mA cm–2.

  • 126. Stress-Relief Network in Silicon Microparticles and Composite Anodes for Durable High-Energy-Density Batteriess ACS Appl. Energy Mater. 4, 9, 10050–10058 (2021)

    Gyujin Song, Myung-Jun Kwak, Chihyun Hwang, Cheolwon An, Suhee Kim, Sangyeop Lee, Sungho Choi, Hyun-Kon Song*, Ji-Hyun Jang*, and Soojin Park*

    Silicon microparticles (SiMPs), which have a high capacity, a high initial Coulombic efficiency, and a low volume-tosurface ratio compared with nanosized materials, are promising anode materials for high-energy-density battery applications. However, SiMPs suffer from inevitable particle pulverization and electrode failure at the early cycle. In this study, we suggest the construction of a porous, stress-relief carbon network on the surface of each SiMP to alleviate particle degradation at the electrode level through a template-free co-reaction of thermal polymer pyrolysis and graphitization. The designed porous graphitic carbon network (pGN) structure features not only considerable electrical conductivity and expansion tolerance but also sturdy SiMP interconnection during cycling. This enables SiMPs to improve battery performance and achieve high Coulombic efficiency and a stable cycle life in fast charging systems without particle dissipation. Moreover, the composite anode comprising a practical level of commercial graphite and SiMP contents with pGN operates effectively because of high cycle efficiency and structural integrity, which promises the realization of advanced battery applications.

  • 125. In situ visualization of zinc plating in gel polymer electrolyte Electrochimica Acta 391, 138877 (2021)

    Yuju Jeon, Yutong Wu, Yamin Zhang, Chihyun Hwang, Hyun-Wook Lee*, Hyun-Kon Song* and Nian Liu*

    Uniform zinc metal plating has been raised as a critical issue in zinc-based batteries. Randomly localized ions lead to severe zinc dendrite formation in liquid electrolyte due to nonuniform ion flux caused by electroconvective flow. One of the mitigating approaches is to use gel polymer electrolyte to regulate the ion flux for suppressing zinc dendrites by imparting viscoelasticity to the electrolyte and improving the ion transport along charged functional groups of polymer chains. However, to this date, the effectiveness of gel polymer electrolyte has been visualized using ex situ methods (e.g., scanning electron microscopy) that requires cell disassembly. And the underlying mechanism is poorly understood. Herein, we applied in situ optical microscopy with dark-field illumination and a transparent glass slide cell to visualize zinc metal plating in the gel polymer electrolyte. At a given current density, the morphological differences of plated zinc metal between the liquid and gel polymer electrolytes were compared. Our in situ optical microscopy platform successfully showed that the gel polymer electrolyte supported by cross linked polyacrylic acid (PAA)/N,N’ methylenebisacrylamide (MBA) polymer framework significantly suppressed the dendrite formation in contrast to the liquid electrolyte during plating. In addition, at various current densities, the tendency of dendritic growth was observed and statistically compared in both electrolytes. The findings will be useful for future design of rechargeable zinc-based batteries.

  • 124. Double activation of oxygen intermediates of oxygen reduction reaction by dual inorganic/organic hybrid electrocatalysts Nano Energy 86, 106048 (2021)

    Dong-GyuLee, Su HwanKim, Jiyun Lee, Seokmin Shin, Se Hun Joo, Yeongdae Lee, Chanhyun Park, Youngkook Kwon, Sang Kyu Kwak,* Hyun-Kon Song*

    Synergistic effects of dual homogeneous catalysts for chemical reactions have been reported. Double activation (chemical transformation process where both catalysts work in concert to activate reactants or intermediates) was often responsible for the synergistic effects of dual catalyst systems. Herein, we demonstrate the extension of the double activation from chemo-catalysis to electrocatalysis. The activity of low-cost cobalt oxide electrocatalysts for oxygen reduction reaction (ORR) was significantly improved by introducing secondary-amine-conjugated polymers (HN-CPs) as the secondary promoting electrocatalyst (shortly, promoter). It was proposed that HN-CPs activated neutral diatomic oxygen to partially charged species (O2δ-) in the initial oxygen adsorption step of ORR. Electron donation number of HN-CP to diatomic oxygen (δ in O2δ-) well described the order of activity improvement, i.e., polypyrrole (pPy) > polyaniline (pAni) > polyindole (pInd). The maximum overpotential gain at ~150 mV was achieved by using pPy with the highest δ. Also, it was confirmed that proton of HN-CP was transferred to single oxygen intermediate (*O) of ORR.

  • 123.Electrochemically Induced Crystallite Alignment of Lithium Manganese Oxide to Improve Lithium Insertion Kinetics for Dye-Sensitized Photorechargeable Batteries ACS Energy Letter. 6, 1198-1204 (2021)

    Myeong-Hee Lee, Byung-Man Kim, Yeongdae Lee, Hyun-Gyu Han, Minjae Cho, Tae-Hyuk Kwon*, and Hyun-Kon Song*

    The insertion of lithium into lithium manganese oxide spinel (LiMn2O4 (LMO) to Li2Mn2O4 (L2MO)) was used to store light energy as a form of chemical energy in a dye-sensitized photorechargeable battery (DSPB). Herein, we investigate the effect of crystallite size of LMO on DSPB performance. The crystallite size of graphene-wrapped submicrometer-sized LMO (LMO@Gn) was tuned electrochemically from 26 to 34 nm via repeated LMO-to-L2MO transitions. The different crystallite orientations in LMO@Gn particles were ordered in an identical direction by an electric stimulus. The LMO@Gn having a 34 nm crystallite size (L34 and L34*) improved DSPB performances in dim light, compared with the smaller-crystallite LMO@Gn (L26). The overall energy efficiency (ηoverall) of 13.2%, higher than ever reported, was achieved by adopting the fully crystallized and structure-stabilized LMO@Gn (L34*) for DSPB. The phase transition between the cubic and tetragonal forms during the LMO-to-L2MO reaction was suspected to be responsible for the structural ordering.

  • 122.A dismutase-biomimetic bifunctional mobile catalyst for anti-aging lithium–oxygen batteries J. Power Sources 492, 229633 (2021)

    Jonghak Kim, Gwan Yeong Jung, Chihyun Hwang, Jinhyeon Jeong, Kyungeun Baek, Jeongin Lee, Seok, Ju Kang, Sang Kyu Kwak,* Hyun-Kon Song*

    Aprotic lithium-oxygen batteries (LOBs) have been considered as one of the high-energy-density alternatives to replace currently available lithium ion batteries. Highly reactive superoxide as the discharge intermediate of LOBs triggers side reactions to deteriorate LOB performances. Also, high overpotential is required to oxidize the discharge product Li2O2 during charge due to the non-conductive nature of Li2O2. Herein, we present 4-carboxy-(2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO-COOH) as a superoxide dismutase mimetic bifunctional mobile catalyst soluble in electrolytes for improving LOB performances. The role of TEMPO-COOH is two-fold: (1) the chemo-catalyst to catalyze superoxide disproportionation reaction for suppressing the superoxide-triggered side reactions during discharge; and (2) the redox mediator to oxidize Li2O2 in a kinetically effective way for reducing the overpotential during charge. The use of the mobile catalyst in LOB cells resulted in the 4-fold increase in cycle life from 50 cycles to 200 cycles as well as the 4-fold increase in the discharge capacity, significantly reducing the overpotential during charge.

  • 121.Metal-Ion Chelating Gel Polymer Electrolyte for Ni-Rich Layered Cathode Materials at a High Voltage and an Elevated Temperature ACS Appl. Mater. Interfaces 13, 9965-9974 (2021)

    Yoon-Gyo Cho, Seo Hyun Jung, Jihong Jeong, Hyungyeon Cha, Kyungeun Baek, Jaekyung Sung, Minsoo Kim, Hyun

    Tae Lee, Hoyoul Kong, Jaephil Cho, Seok Ju Kang, Jong Mok Park*, and Hyun-Kon Song*

    Nickel-rich layered oxides (LiNi1–x–yCoxMnyO2; (1 – x – y) ≥ 0.6), the high-energy-density cathode materials of lithium-ion batteries (LIBs), are seriously unstable at voltages higher than 4.5 V versus Li/Li+ and temperatures higher than 50 °C. Herein, we demonstrated that the failure mechanism of a nickel-rich layered oxide (LiNi0.6Co0.2Mn0.2O2) behind the instability was successfully suppressed by employing cyanoethyl poly(vinyl alcohol) having pyrrolidone moieties (Pyrd-PVA-CN) as a metal-ion-chelating gel polymer electrolyte (GPE). The metal-ion-chelating GPE blocked the plating of transition-metal ions dissolved from the cathode by capturing the ions (anode protection). High-concentration metal-ion environments developed around the cathode surface by the GPE suppressed the irreversible phase transition of the cathode material from the layered structure to the rock-salt structure (cathode protection). Resultantly, the capacity retention was significantly improved at a high voltage and a high temperature. Capacity retention and coulombic efficiency of a full-cell configuration of a nickel-rich layered oxide with graphite were significantly improved in the presence of the GPE especially at a high cutoff voltage (4.4 V) and an elevated temperature (55 °C).

  • 120. Rational design of a redox-active mixed ion/electron conductor as a multi-functional binder for lithium ion batteries J. Mater. Chem. A 9, 4751-4757 (2021)

    Chihyun Hwang, Jungho Lee, Jihong Jeong, Eunryeol Lee, Jonghak Kim, seoyoung Kim, Changduk Yang* and Hyun-Kon Song*

    A redox-active mixed ion and electron conductor (redox-active MIEC) is presented as a binder for lithium titanate anode of lithium-ion batteries. The redox-active MIEC binder (symbolized by PT*-GmCn) was designed to be (1) electrically conductive along its conjugated thiophene backbone (PT = polythiophene), (2) redox-active from its succinimide moiety (* = redox-active) and (3) ionically conductive by adopting glyme (G) branches. It was superior to the practically used PVdF binder in terms of lithium ion diffusivity and electric conductivity (1.4 x and 15,000 x, respectively). High capacity was guaranteed especially at high rates due to its MIEC nature of PT*-GmCn while additional capacity was achieved from its redox activity.

  • 119. Support structure-catalyst electroactivity relation for oxygen reduction reaction on platinum supported by two-dimensional titanium carbide Nano Energy 79, 105363 (2021)

    Yeongdae Lee, Jang Hyuk Ahn, Hee-Young Park, Jeawoo Jung, Yuju Jeon, Dong-Gyu Lee, Min-Ho Kim, Eunryeol Lee, Chanseok Kim, Youngkook Kwon, Hyun-Wook Lee, Jong Hyun Jang, Jun Hee Lee*, Hyun-Kon Song*

    It is demonstrated that the electroactivity of the oxygen reduction reaction (ORR) of Pt depends on the structure of a support. Highly conductive two-dimensional titanium carbide (Ti3C2) was selected as the support for Pt because of the expected strong metal-support interaction (SMSI) between Pt and Ti. To control the edge-to-basal ratio, the number of Ti3C2 layers was modulated by exfoliation. Pt nanoparticles (4 nm) were loaded on three different Ti3C2 supports including multi-, few-, and mono-layered Ti3C2 (22L-, 4L-, and 1L-Ti3C2, respectively). The edge-to-basal ratio of layered Ti3C2 increased as the number of layers increased. The edge-dominant support (22L-Ti3C2) donated more electrons to Pt than the basal-dominant supports (4L-Ti3C2 and 1L-Ti3C2). As a result, electron-rich Pt with less d-band vacancies (e.g., Pt/22L-Ti3C2) showed higher ORR activity. In addition, the electron transfer from the support to Pt inducing the strong interaction between Pt and Ti improved the durability of the ORR electroactivity of Pt.

  • 118. Design of a Janus‐Faced Electrode for Highly Stretchable Zinc–Silver Rechargeable Batteries Advanced Functional Materials 30, 2004137 (2020)

    Woo-Jin Song, Chihyun Hwang, Sangyeop Lee, Minsik Kong, Jonghak Kim, Hyung Keun Park, Hye Bin Son, Gyeongbae Park, Sunghwan Cho, Jun Hyuk Song, Hyoung Seop Kim, Unyong Jeong, Tae Joo Shin,* Hyun-Kon Song,* and Soojin Park*

    One of the biggest challenges facing the development of comfortable wearable electronics is the fabrication of stretchable power sources, which are inherently safe and can maintain their electrochemical performance under mechanical elongation. Zinc–silver batteries based on water‐based chemistry have been investigated as viable power supply candidates, owing to their high energy/power density and safety. However, this type of batteries requires a new electrode that can guarantee both high elasticity and stable cycling characteristics of the battery. Here, stretchable zinc–silver rechargeable batteries based on a Janus‐faced electrode, which is a single electrode that comprises a cathode and an anode, are proposed. The Janus‐faced electrode exhibits good mechanical robustness (200 cycles at 200% strain) and retains a high electrical conductivity in the elongated state (2.1 Ω at 100% strain). A proof‐of‐concept stretchable zinc–silver battery based on the Janus‐faced electrode is fabricated to demonstrate the outstanding long‐term cyclability (capacity retentions of ≈90% after 200 cycles), owing to the prevention of short circuit from the zinc dendrite by the unique electrode configuration. Further, the proposed stretchable zinc–silver batteries can deliver a stable electrochemical performance even under a 200% strain while maintaining their functional properties.

  • 117. Rational Structure Design of Fast-Charging NiSb Bimetal Nanosheet Anode for Lithium Ion Batteries Energy & Fuels 34, 8, 10211–10217 (2020)

    Gyujin Song, Sungho Choi, Chihyun Hwang, Jaegeon Ryu, Woo-Jin Song, Hyun-Kon Song, and Soojin Park*

    Although bimetallic materials with various structures have been used as anodes for advanced lithium ion batteries, structural degradation, caused during electrochemical reactions, leads to a shorter cycle lifespan. Herein, we propose a rational structural design, carbon-wrapped porous bimetallic nickel–antimony nanosheets (NiSbNS@C), with the help of dual-functional organic acid acting as a reducing agent and a carbon coating source upon the synthetic process. The structural evolution of NiSbNS@C is further confirmed as the NiSb crystal is transformed into a Ni-rich phase on fast charging. A well-constructed NiSbNS@C electrode exhibits outstanding high rate performance and structure stability owing to the fast electrochemical kinetics of the porous NiSb nanostructure and uniform carbon decoration in both half and full cells. This approach opens up an avenue to make a desirable structure for bimetallic anode materials toward high rate and stable lithium ion batteries.

  • 116. Pyridinic-to-graphitic conformational change of nitrogen in graphitic carbon nitride by lithium coordination during lithium plating Energy Storage Materials 31, 505-514 (2020)

    Yuju Jeon, Sujin Kang, Se Hun Joo, Minjae Cho, Sung O. Park, Nian Liu,* Sang Kyu Kwak,* Hyun-Wook Lee* and Hyun-Kon Song*

    The reversibility of lithium plating/stripping should be guaranteed in lithium metal batteries. Seriously localized lithium growth during plating leads to the dendritic evolution of lithium metal due to the uneven current distribution on the electrically conductive surface. Artificial protective layers covering electrodes (e.g., polymer film on copper foil) have been used to narrow the gap of the current density between positions on the conductive surface. Herein, we incorporated an active ingredient to attract lithium ions into the dendrite-suppressing layer. Pyridinic nitrogen of graphitic carbon nitride (g-C3N4) served as the lithium ion affinity center. Conformation of the nitrogen changed from pyridinic to graphitic in the presence of lithium ions, which confirms the coordination of lithium ion to the pyridinic nitrogen. Moreover, lithium ion conduction was facilitated in the presence of g-C3N4 layer probably via a site-to-site hopping mechanism. Lithium metal was plated between the g-C3N4 layer and the copper current collector (or the lithium metal). The homogeneous lithium nucleation expected from the active role of the pyridinic nitrogen (lithium ion affinity and facilitated ionic conduction) suppressed the dendritic growth of lithium metal and decreased the overpotential required for the initial metal nucleation. Due to the top-down ion flux regulation on the uppermost surface (or tip) of lithium metal, the reversibility of lithium plating/stripping was dramatically improved.

  • 115. A Three-Dimensional Nano-web Scaffold of Ferroelectric Beta-PVDF Fibers for Lithium Metal Plating and Stripping ACS Applied Materials & Interfaces, 12, 26, 29235–29241 (2020)

    Chihyun Hwang, Woo-Jin Song, Gyujin Song, Yutong Wu, Sangyeop Lee, Hye Bin Son, Jonghak Kim, Nian Liu*, Soojin Park*, and Hyun-Kon Song*

    Lithium metal has been considered as an anode material to improve energy densities of lithium chemistry-based rechargeable batteries (that is to say, lithium metal batteries or LMBs). Higher capacities and cell voltages are ensured by replacing practically used anode materials such as graphite with lithium metal. However, lithium metal as the LMB anode material has been challenged by its dendritic growth, electrolyte decomposition on its fresh surface, and its serious volumetric change. To address the problems of lithium metal anodes, herein, we guided and facilitated lithium ion transport along a spontaneously polarized and highly dielectric material. A three-dimensional web of nanodiameter fibers of ferroelectric beta-phase polyvinylidene fluoride (beta-PVDF) was loaded on a copper foil by electrospinning (PVDF#Cu). The electric field applied between the nozzle and target copper foil forced the dipoles of PVDF to be oriented centro-asymmetrically and then the beta structure induced ferroelectric polarization. Three-fold benefits of the ferroelectric nano-web architecture guaranteed the plating/stripping reversibility especially at high rates: (1) three-dimensional scaffold to accommodate the volume change of lithium metal during plating and stripping, (2) electrolyte channels between fibers to allow lithium ions to move, and (3) ferroelectrically polarized or negatively charged surface of beta-PVDF fibers to encourage lithium ion hopping along the surface. Resultantly, the beta-PVDF web architecture drove dense and integrated growth of lithium metal within its structure. The kinetic benefit expected from the ferroelectric lithium ion transport of beta-PVDF as well as the porous architecture of PVDF#Cu was realized in a cell of LFP as a cathode and lithium-plated PVDF#Cu as an anode. Excellent plating/stripping reversibility along repeated cycles was successfully demonstrated in the cell even at a high current such as 2.3 mA cm–2, which was not obtained by the nonferroelectric polymer layer.

  • 114. An Antiaging Electrolyte Additive for High-Energy-Density Lithium-Ion Batteries Advanced Energy Materials, 10, 200563 (2020)

    Jung-Gu Han, Chihyun Hwang, Su Hwan Kim, Chanhyun Park, Jonghak Kim, Gwan Yeong Jung, Kyungeun Baek, Sujong Chae, Seok Ju Kang, Jaephil Cho, Sang Kyu Kwak,* Hyun-Kon Song,* and Nam-Soon Choi*

    High‐capacity Li‐rich layered oxide cathodes along with Si‐incorporated graphite anodes have high reversible capacity, outperforming the electrode materials used in existing commercial products. Hence, they are potential candidates for the development of high‐energy‐density lithium‐ion batteries (LIBs). However, structural degradation induced by loss of interfacial stability is a roadblock to their practical use. Here, the use of malonic acid‐decorated fullerene (MA‐C60) with superoxide dismutase activity and water scavenging capability as an electrolyte additive to overcome the structural instability of high‐capacity electrodes that hampers the battery quality is reported. Deactivation of PF5 by water scavenging leads to the long‐term stability of the interfacial structures of electrodes. Moreover, an MA‐C60‐added electrolyte deactivates the reactive oxygen species and constructs an electrochemically robust cathode‐electrolyte interface for Li‐rich cathodes. This work paves the way for new possibilities in the design of electrolyte additives by eliminating undesirable reactive substances and tuning the interfacial structures of high‐capacity electrodes in LIBs.

  • 113. Indoor-Light-Energy-Harvesting Dye-Sensitized Photo-Rechargeable Battery Energy & Environmental Science, 13, 1473 - 1480 (2020)

    Byung-Man Kim, Myeong-Hee Lee, Vijayan Sobhana Dilimon, Jeong-Soo Kim, Jung Seung Nam, Yoon-Gyo Cho, Hyun Kuk Noh, Deok-Ho Roh, Tae-Hyuk Kwon* and Hyun-Kon Song*

    Photo-rechargeable batteries (PRBs) benefit from their bifunctionality covering energy harvest and storage. However, dim-light performances of the PRBs for indoor applications have not been illuminated. Herein, we present an external-power-free single-structured PRB named dye-sensitized photo-rechargeable battery (DSPB) with an outstanding light-to-charge energy efficiency (ηoverall) of 11.5% at dim light condition. This unprecedented ηoverall was attributed to thermodynamically-favorable design of the DSPB to maximize the working potential. At high-power irradiation, the kinetically-fast but thermodynamically-unfavorable iodine mediator (I−/I3−) showed the highest charge and discharge capacities even if its discharge voltage was lowest. In a dim-light for indoor applications, however, the thermodynamically-favorable but kinetically-slow copper complex mediator (Cu+/2+(dmp)2) showed the energy density and efficiency superior to I−/I3− because its kinetics did not limit the harvesting capacity. The successful demonstration of the DSPB to operate a temperature-sensing IoT device only by an indoor light opens the possibility of realizing indoor-light-harvesting PRBs.

  • 112. A Bipolymer-Crosslinked Binder to Improve the Reversibility and Kinetics of Sodiation and Desodiation of Antimony for Sodium Ion Batteries ACS Applied Materials & Interfaces 11, 46, 43039-43045 (2019)

    Dohyoung Kim, Chihyun Hwang,* Jihong Jeong, Woo-Jin Song, Soojin Park and Hyun-Kon Song*

    Although the volume of antimony tremendously expands during the alloying reaction with sodium, it is considered a promising anode material for sodium ion batteries (SIBs). Repeated volume changes along the sodiation/desodiation cycles encourage capacity fading by triggering pulverization accompanying electrolyte decomposition. Additionally, the low cation transference number of sodium ions is another hindrance for application in SIBs. In this work, a binder was designed for the antimony in SIB cells to ensure bifunctionality and improve (1) the mechanical toughness to suppress the serious volume change and (2) the transference number of sodium ions. A crosslinked composite of poly(acrylic acid) and cyanoethyl pullulan (pullulan-CN) was presented as the binder. The polysaccharide backbone of pullulan-CN was responsible for the mechanical toughness, while the cyanoethyl groups of pullulan-CN improved the lithium cation transfer. The antimony-based SIB cells using the composite binder showed improved cycle life with enhanced kinetics. The capacity was maintained at 76% of the initial value at the 200th cycle of 1C discharge following 1C charge, while the capacity at 20C was 61% of the capacity at 0.2C, implying that the composite binder significantly improved the sodiation/desodiation reversibility of antimony.

  • 111. A Biomimetic Superoxide Disproportionation Catalyst for Anti-Aging Lithium-Oxygen Batteries ACS Nano 13, 8, 9190-9197 (2019)

    Chihyun Hwang, JongTae Yoo, Gwan Yeong Jung, Se Hun Joo, Jonghak Kim, Aming Cha, Jung-Gu Han, Nam-Soon Choi, Seok Ju Kang, Sang-Young Lee, Sang Kyu Kwak and Hyun-Kon Song

    Reactive oxygen species or superoxide (O2-) to damage or age biological cells is generated during metabolic pathways using oxygen as an electron acceptor in biological systems. Superoxide dismutase (SOD) protects cells from the superoxide-triggered apoptosis by converting superoxide to oxygen and peroxide. Lithium-oxygen battery (LOB) cells have the same aging problems caused by superoxide-triggered side reactions. We transplanted the function of SOD of biological systems into LOB cells. Malonic acid-decorated fullerene (MAC60) was used as a superoxide disproportionation chemo-catalyst mimicking the function of SOD. As expected, MA-C60 as the superoxide scavenger improved capacity retention along charge/discharge cycles successfully. A LOB cell that failed to provide a meaningful capacity just after several cycles at high current (0.5 mA cm-2) with 0.5 mAh cm-2 cut-off survived up to 50 cycles after MA-C60 was introduced to electrolyte. Moreover, the SOD-mimetic catalyst increased capacity: e.g., more than six-fold increase at 0.2 mA cm-2. Experimentally observed toroidal morphology of the final discharge product of oxygen reduction (Li2O2) and density functional theory calculation confirmed that the solution mechanism of Li2O2 formation, more beneficial than the surface mechanism from the capacity-gain standpoint, was preferred in the presence of MA-C60

  • 110.Atomic-scale combination of germanium-zinc nanofibers for structural and electrochemical evolution Nature Communications 10, 2364 (2019)

    Gyujin Song, Jun Young Cheong, Chanhoon Kim, Langli Luo, Chihyun Hwang, Sungho Choi, Jaegeon Ryu, Sungho Kim, Woo-Jin Song, Hyun-Kon Song, Chongmin Wang, Il-Doo Kim & Soojin Park

    Alloys are recently receiving considerable attention in the community of rechargeable batteries as possible alternatives to carbonaceous negative electrodes; however, challenges remain for the practical utilization of these materials. Herein, we report the synthesis of germanium-zinc alloy nanofibers through electrospinning and a subsequent calcination step. Evidenced by in situ transmission electron microscopy and electrochemical impedance spectroscopy characterizations, this one-dimensional design possesses unique structures. Both germanium and zinc atoms are homogenously distributed allowing for outstanding electronic conductivity and high available capacity for lithium storage. The as-prepared materials present high rate capability (capacity of ~ 50% at 20 C compared to that at 0.2 C-rate) and cycle retention (73% at 3.0 C-rate) with a retaining capacity of 546 mAh g−1

  • 109.Toward Fast Operation of Lithium Batteries : Ion Activity as the Factor To Determine the Concentration Polarization ACS Energy Letters 4, 1265-1270 (2019)

    Dong-Hui Kim, Sunwook Hwang, Jeong-Ju Cho, Sunghoon Yu, Soojin Kim, Jongho Jeon, Kyoung Ho Ahn, Chulhaeng Lee, Hyun-Kon Song, Hochun Lee*

    The concentration polarization, in addition to the activation and ohmic polarizations, limits the fast operation of electrochemical cells such as Li-ion batteries (LIBs). We demonstrate an approach to mitigate the concentration polarization by regulating the effective concentration (i.e., the mean ionic activity) of Li ions. The use of an acrylate-based gel polymer electrolyte (A-GPE) improved the rate capability of LIBs compared with its liquid counterpart. Electrochemical and spectroscopic evidence confirms that the unexpected power performance of the A-GPE is ascribed to the unique solvation structure surrounding the Li ions. The solvation structure suppresses an abnormal increase in the activity of Li ions and thus mitigates the concentration polarization during high-rate discharge. Importantly, this study rejects the common wisdom that the solid or semisolid electrolytes discourage the fast charge/discharge of LIBs and suggests an avenue to simultaneously enhance both the safety and high-power performance of rechargeable batteries.

  • 108.Metamorphosis of Seaweeds into Multitalented Materials for Energy Storage Applications Advanced Energy Materials 9, 1900570 (2019)

    Myoungsoo Shin, Woo-Jin Song, Jung-Gu Han, Chihyun Hwang, Sangyeop Lee, Seokkeun Yoo, Sewon Park, Hyun-Kon Song, Seungmin Yoo,* Nam-Soon Choi,* and Soojin Park*

    Transition metal ion dissolution due to hydrofluoric acid attack is a long-standing issue in the Mn-based spinel cathode materials of lithium-ion batteries (LIBs). Numerous strategies have been proposed to address this issue, but only a fragmentary solution has been established. In this study, reported is a seaweed-extracted multitalented material, namely, agar, for high-performance LIBs comprising Mn-based cathode materials at a practical loading density (23.1 mg cm−2 for LiMn2O4 and 10.9 mg cm−2for LiNi0.5Mn1.5O4, respectively). As a surface modifier, 3-glycidoxypropyl trimethoxysilane (GPTMS) is employed to enable the agar to have different phase separation behaviors during the nonsolvent-induced phase separa-tion process, thus eventually leading to the fabrication of an outstanding separator membrane that features a well-defined porous structure, superior mechanical robustness, high ionic conductivity, and good thermal stability. The GPTMS-modified agar separator membrane coupled with a pure agar binder to the LiNi0.5Mn1.5O4/graphite full cell leads to exceptional improve-ment in electrochemical performance outperforming binders and separator membrane in current commercial products even at 55 °C; this improvement is due to beneficial features such as Mn2+ chelation and PF5 stabilizing capa-bilities. This study is believed to provide insights into the potential energy applications of natural seaweeds.

  • 107.Production of germanium nanoparticles via laser pyrolysis for anode materials of lithium-ion batteries and sodium-ion batteries Nanotechnology 30, 27 (2019).

    Tae-Hee Kim, Hyun-Kon Song*, Seongbeom Kim*

    Germanium nanoparticles were synthesized and subjected to a study as anode materials for lithium ion batteries and sodium ion batteries. Laser pyrolysis of GeH4 was used to produce germanium nanoparticles and the average diameter of germanium nanoparticles was easily controlled by regulating sensitizer gas flow rates during the process. 60 and 10 nm size nanoparticles were synthesized and micron-size powders was purchased and these 3 different sizes of pure germanium powder samples were tested as anode materials of lithium ion batteries and sodium ion batteries in terms of cycle retention, long term cycle and kinetics of reaction. Experimental results showed that the smallest powder sample which is synthesized, average 10 nm, exhibited excellent performances in both kinds batteries. According to the results, characteristics of batteries became better as the size of germanium powders decreased consistently. Pure germanium was thoroughly investigated as an anode of metal-ion batteries regarding to its powder size. Experimental data and a synthesis approach of germanium nanoparticles suggested in this research would be an good example in utilization of elemental germanium for high performance batteries.

  • 106. Nanobead-reinforced outmost shell of solid-electrolyte interphase layers for suppressing dendritic growth of lithium metal Journal of Power Sources 414, 218-224 (2019).

    Minsoo Kim, Yuju Jeon, Yoon-Gyo Cho, and Hyun-Kon Song*

    Plating-stripping reversibility of lithium metal is improved by reinforcing the solid-electrolyte interphase layer by inorganic nanobeads. The outmost solid-electrolyte interphase shell is clearly identified, which is the passive layer formed on current collectors (or lithium metal) before the first lithium metal deposition. The outmost shell is intrinsically brittle and fragile so that it is easily broken by lithium metal dendrites growing along the progress of plating. Lithium metal deposit is not completely stripped back to lithium ions. On the other hand, lithium metal cells containing inorganic nanobeads in electrolyte show high reversibility between plating and stripping. The nanobeads are incorporated into the outmost shell during its formation. The nanobead-reinforced outmost shell having mechanically durable toughness suppresses dendritic growth of lithium metal, not allowing the dendrites to penetrate the shell. In addition to the mechanical effect of nanobeads, the LiF-rich solid-electrolyte interphase layer formation is triggered by HF generated by the reaction of the moisture adsorbed on oxide nanobeads with PF6−. The LiF-rich composition is responsible for facile lithium ion transfer through the passive layers.

  • 105. A Hierarchically Structured Multi-dimensional Carbon Composite Anchored to Polymer Mat for Super-flexible Supercapacitor ACS Applied Energy Materials 2, 389–397 (2019)

    Yeongdae Lee, Myung-Jun Kwak, Chihyun Hwang,* Cheolwon An, Woo-Jin Song, Gyujin Song, Suhee Kim, Soojin Park, Ji-Hyun Jang,* and Hyun-Kon Song*

    A carbon electrode was designed to guarantee flexibility of symmetric electric double layer capacitors (EDLCs) based on its architecture. Three different dimensional carbon materials were combined to achieve the flexibility without sacrificing high performances: highly capacitive but poorly-conductive three-dimensional graphene (3D-Gn*) as a platform for electric double layer formation, one-dimensional carbon nanotube (1D-CNT) as an electrically conductive highway and two dimensional graphene (2D-Gn) for facilitating electron communications between 3D-Gn* and 1D-CNT. From a mechanical standpoint, the 1D-CNT provided an intertangled framework to integrate the main active material 3D-Gn* and anchored the active layer to a flexible polymer matrix. Resultantly, the symmetric EDLC based on the hierarchically structured multi-dimensional carbon electrodes anchored to flexible substrates was operated successfully at 3 V, ensuring high energy densities even under repetitive mechanical stress conditions.

  • 104. Binary N,S-doped carbon nanospheres from bio-inspired artificial melanosomes: Route to efficient air electrodes for seawater batteries Journal of Materials Chemistry A 6, 24459 (2018).

    Ziyauddin Khan, Sung O Park, Juchan Yang, Seungyoung Park, Ravi Shanker, Hyun-Kon Song, Youngsik Kim, Sang Kyu Kwak* and Hyunhyub Ko*

    immense potential for future energy storage devices; however, lack of high-performance negative and positive electrodes significantly challenges their practical applications. In this study, N-doped and N,S-doped carbon nanospheres (referred to as NCS and NSCS, respectively) are synthesized via the pyrolysis of melanosomes, which are bio-inspired polymers. Electrocatalytic activity measurements reveal the bifunctionality of the prepared catalysts. NSCS exhibit a distinctively higher performance when used as a air electrode in seawater batteries to NCS at ambient condition (refered as static mode hereafter). Further, by the introduction of air flow into the seawater electrolyte (refered as flow mode hereafter), NSCS exhibits an improved cell discharge potential. The high performnce of cell is attributed to high surface area; bifunctional electrocatalytic activity; generation of new active sites; improvement of spin density in NSCS; and continuous flow of air to the electrolyte. The cell in the flow mode exhibits an overpotential gap of 0.56 V, a round-trip efficiency of 84%, a maximum power density of 203 mW g−1, and an outstanding cyclic stability of up to 100 cycles. The developed synthetic method provides an effective, scalable approach for the doping of binary or ternary atoms into the carbon host matrix, which can motivate further experimental and theoretical studies of electrode materials in various energy storage devices. In addition, the concept and results obtained by the introduction of air flow into the electrolyte can lead to the improvement of cell performance in terms of electrical energy efficiency, which can be exploited in various metal–air battery.

  • 103. A metal-ion-chelating organogel electrolyte for Le Chatelier depression of Mn3+ disproportionation of lithium manganese oxide spinel Journal of Materials Chemistry A 6, 22483 - 22488 (2018).

    Yoon-Gyo Cho, Seo-Hyun Jung, Se Hun Joo, Yuju Jeon, Minsoo Kim, Kyung Min Lee, Seungmin Kim, Jong Mok Park, Hyun Kuk Noh, Young-Soo Kim, Jung-Eui Hong, Sang-Ik Jeon, Taewon Kim, Sang Kyu Kwak*, Hoyoul Kong*, Hyun-Kon Song*

    We present a metal-ion-chelating organogel electrolyte, thermally gelated within cells, to solve the problems triggered by metal dissolution from cathodes of lithium ion batteries. The organogel significantly improved the capacity retention of lithium manganese oxide spinel during cycling. The organogel mitigated metal deposition on anodes by capturing metal ions (anode protection). Interestingly, the organogel inhibited metal dissolution by keeping dissolved metal ions highly concentrated around the cathode surface (cathode protection by Le Chatelier's principle).

  • 102. Gel/Solid Polymer Electrolytes Characterized by In Situ Gelation or Polymerization for Electrochemical Energy Systems Advanced Materials, 31, 1804909 (2019).

    Yoon-Gyo Cho, Chihyun Hwang, Do Sol Cheong, Young‐Soo Kim*, Hyun‐Kon Song*

    A gel polymer electrolyte (GPE) is a liquid electrolyte (LE) entrapped by a small amount of polymer network less than several wt%, which is characterized by properties between those of liquid and solid electrolytes in terms of the ionic conductivity and physical phase. Electrolyte leakage and flammability, demerits of liquid electrolytes, can be mitigated by using GPEs in electrochemical cells. However, the contact problems between GPEs and porous electrodes are challenging because it is difficult to incorporate GPEs into the pores and voids of electrodes. Herein, the focus is on GPEs that are gelated in situ within cells instead of covering comprehensive studies of GPEs. A mixture of LE and monomer or polymer in a liquid phase is introduced into a pre‐assembled cell without electrolyte, followed by thermal gelation based on physical gelation, monomer polymerization, or polymer cross‐linking. Therefore, GPEs are formed omnipresent in cells, covering the pores of electrode material particles, and even the pores of separators. As a result, different from ex situ formed GPEs, the in situ GPEs have no electrode/electrolyte contact problems. Functional GPEs are introduced as a more advanced form of GPEs, improving lithium‐ion transference number or capturing transition metals released from electrode materials.

  • 101. Sphere‐to‐Multipod Transmorphic Change of Nanoconfined Pt Electrocatalyst during Oxygen Reduction Reaction Small 15, 1802228 (2019).

    Juchan Yang, Dongwoo Kang, Yuju Jeon, Jong Hoon Lee, Hu Young Jeong*, Hyeon Suk Shin*, Hyun‐Kon Song*

    An oxygen reduction reaction (ORR) catalyst/support system is designed to have Pt nanoparticles nanoconfined in a nanodimensionally limited space. Holey crumpled reduced graphene oxide plates (hCR‐rGO) are used as a carbon support for Pt loading. As expected from interparticular Pt‐to‐Pt distance of Pt‐loaded hCR‐rGO longer than that of Pt/C (Pt‐loaded carbon black as a practical Pt catalyst), the durability of ORR electroactivity along cycles is improved by replacing the widely used carbon black with hCR‐rGO. Unexpected morphological changes of Pt are electrochemically induced during repeated ORR processes. Spherical multifaceted Pt particles are evolved to {110}‐dominant dendritic multipods. Nanoconfinement of a limited number of Pt within a nanodimensionally limited space is responsible for the morphological changes. The improved durability observed from Pt‐loaded hCR‐rGO originates from 1) dendritic pod structure of Pt exposing more active sites to reactants and 2) highly ORR‐active Pt {110} planes dominant on the surface.

  • 100. RuO2 nanocluster as a 4-in-1 electrocatalyst for hydrogen and oxygen electrochemistry Han-Saem Park, Juchan Yang, Min Kyung Cho, Yeongdae Lee, Seonghun Cho, Sung-Dae Yim, Byeong-Su Kim, Jong Hyun Jang*, Hyun-Kon Song*
    Nano Energy 55, 49-58 (2019).

    Partially hydrous RuO2 nanocluster embedded in a carbon matrix (x-RuO2@C with x = hydration degree = 0.27 or 0.27@C) is presented as a bifunctional catalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) for water splitting. Symmetric water electrolyzers based on 0.27-RuO2@C for both electrodes showed smaller potential gaps between HER and OER at pH 0, pH 14 and even pH 7 than conventional asymmetric electrolyzers based on two different catalysts (Pt/C || Ir/C) that have been known as the best catalysts for HER and OER respectively. Moreover, 0.27-RuO2@C showed another bifunctional electroactivity for fuel cell electrochemistry involving hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) that are the backward reactions of HER and OER respectively. Pt-level HOR electroactivity was obtained from 0.27-RuO2@C, while its ORR activity was inferior to that of Pt with 200 mV higher overpotential required. The tetra-functionality of 0.27-RuO2@C showed the possibility of realizing single-catalyst regenerative fuel cells.

  • 99. Nanoporous Films and Nanostructure Arrays Created by Selective Dissolution of Water-Soluble Materials Advanced Science 5, 1800851 (2018).

    Yoon Seo Kim, Jaejung Song, Chihyun Hwang, Xuejing Wang, Haiyan Wang, Judith L. MacManus‐Driscoll*, Hyun‐Kon Song*, Seungho Cho*

    Highly porous thin films and nanostructure arrays are created by a simple process of selective dissolution of a water‐soluble material, Sr3Al2O6. Heteroepitaxial nanocomposite films with self‐separated phases of a target material and Sr3Al2O6. are first prepared by physical vapor deposition. NiO, ZnO, and Ni1−xMgxO are used as the target materials. Only the Sr3Al2O6. phase in each nanocomposite film is selectively dissolved by dipping the film in water for 30 s at room temperature. This gentle and fast method minimizes damage to the remaining target materials and side reactions that can generate impurity phases. The morphologies and dimensions of the pores and nanostructures are controlled by the relative wettability of the separated phases on the growth substrates. The supercapacitor properties of the porous NiO films are enhanced compared to plain NiO films. The method can also be used to prepare porous films or nanostructure arrays of other oxides, metals, chalcogenides, and nitrides, as well as films or nanostructures with single‐crystalline, polycrystalline, or amorphous nature.

  • 98. Mechanical mismatch-driven rippling in carbon-coated silicon sheets for stress-resilient battery anodes Nature Communications 9, 2924 (2018).

    Jaegeon Ryu, Tianwu Chen, Taesoo Bok, Gyujin Song, Jiyoung Ma, Chihyun Hwang, Langli Luo, Hyun-Kon Song, Jaephil Cho, Chongmin Wang, Sulin Zhang, Soojin Park

    High-theoretical capacity and low working potential make silicon ideal anode for lithium ion batteries. However, the large volume change of silicon upon lithiation/delithiation poses a critical challenge for stable battery operations. Here, we introduce an unprecedented design, which takes advantage of large deformation and ensures the structural stability of the material by developing a two-dimensional silicon nanosheet coated with a thin carbon layer. During electrochemical cycling, this carbon coated silicon nanosheet exhibits unique deformation patterns, featuring accommodation of deformation in the thickness direction upon lithiation, while forming ripples upon delithiation, as demonstrated by in situ transmission electron microscopy observation and chemomechanical simulation. The ripple formation presents a unique mechanism for releasing the cycling induced stress, rendering the electrode much more stable and durable than the uncoated counterparts. This work demonstrates a general principle as how to take the advantage of the large deformation materials for designing high capacity electrode.

  • 97. Activity-Durability Coincidence of Oxygen Evolution Reaction in the Presence of Carbon Corrosion: Case Study of MnCo2O4 Spinel with Carbon Black ACS Sustainable Chemistry & Engineering 6, 9566-9571 (2018).

    Juchan Yang, Seungyoung Park, Kyoung young Choi, Han-Saem Park, Yoon-Gyo Cho, Hyunhyub Ko, and Hyun-Kon Song*

    Highly oxygen evolution reaction (OER)-active electrocatalysts often exhibit improved OER durability in the presence of carbon corrosion or oxidation (COR) in the literature. The activity-durability coincidence of OER electrocatalysts was theoretically understood by preferential depolarization in galvanostatic situations. At constant-current conditions for a system involving multiple reactions that are independent and competitive, the overpotential is determined most dominantly by the most facile reaction so that the most facile reaction is responsible for a dominant portion of the overall current. Therefore, higher OER activity improves durability by mitigating the current responsible for COR. The activity-durability coincidence was then proved experimentally by comparing between two catalysts of the same chemical identity (MnCo2O4) in different dimensions (5 and 100 nm in size). Carbon corrosion responsible for inferior durability was suppressed in the smaller-dimension catalyst (MnCo2O4 in 5 nm) having more numbers of active sites per a fixed mass.

  • 96. Nano-perovskite oxide prepared via inverse microemulsion mediated synthesis for catalyst of lithium-air batteries Electrochimica Acta 275, 248-255 (2018).

    Chaehyun Lim, Changmin Kim, Ohhun Gwon, Hu Young Jeong, Hyun-Kon Song, Young-Wan Ju*, Jeeyoung Shin*, and Guntae Kim*

    Perovskite oxides have received considerable attention as useful electro-catalysts for Li-air batteries due to their properties of excellent catalytic activity, electrical conductivity, and durability. The nanostructure can enhance the electrochemical performance of perovskite oxides by enlarging the catalytic active sites. In this study, nano-size Nd0.67Sr0.33CoO3-δ (NSC) perovskite particles with a particle size of 20–50 nm and a specific surface area of 12.759 m2 g-1 were successfully synthesized by a microemulsion method. The NSC perovskite particles exhibit excellent electrocatalytic activity particularly in the oxygen evolution reaction (OER) with a high limiting current density of 33.68 mA cm-2 at 0.9 V vs. (Hg/HgO). This excellent catalytic activity can be ascribed to the existence of Co3+ and the enlarged surface area. Co3+ provides catalytically active site by forming Co3+/4+ redox couple and the enlarged surface increases active sites for reactants and catalyst particles. In this regard, nano-size NSC particles prepared by the microemulsion route provide excellent and stable electrochemical performance in the hybrid Li-air battery.

  • 95. High-performance electrothermal and anticorrosive transparent heating stickers Journal of Materials Chemistry A 6, 11790 (2018).

    Kangmin Lee, Jeonghwan Park, Hyungwoo Kim, Han-Saem Park, Hyun-Kon Song, Ka-Hyun Kim* and Kwanyong Seo*

    In this study, the fabrication of a high-performance electrothermal and anticorrosive transparent heating sticker employing a novel Ni/Ag hybrid microgrid electrode is reported. The proposed sticker not only exhibits an excellent optoelectronic performance (a sheet resistance of 4.3 Ω sq1 at a transmittance of 96%) but also has a uniform heat distribution over its entire area owing to the electrical uniformity of the honeycomb-structured microgrid electrode. The transparent heating sticker reveals outstanding thermal and chemical stability with no electrode damage even in harsh environments such as high temperatures (300 oC) and atmospheres containing sulfur in excess, due to the anti-corrosion properties of nickel (Ni). The transparent heating sticker also exhibits a high saturation temperature of over 100 oC even at a low operating voltage (5 V) because highly thermally/electrically conductive silver (Ag) is employed as a base electrode material underneath Ni. Furthermore, a successful defogging test is demonstrated with an automobile side-view mirror using the transparent heating sticker, confirming its practical applicability. Accordingly, the proposed transparent heating sticker presents a unique opportunity for developing transparent heaters with superior chemical stability and a high electrothermal performance.

  • 94. Contorted polycyclic aromatic hydrocarbon: promising Li insertion organic anode Journal of Materials Chemistry A 6, 12589 (2018).

    Jaehyun Park, Cheol Woo Lee, Se Hun Joo, Ju Hyun Park, Chihyun Hwang, Hyun-Kon Song, Young Seok Park, Sang Kyu Kwak,* Seokhoon Ahn* and Seok Ju Kang*

    Enhancing the performance of carbon-based anode materials in Li-ion battery (LIB) systems is of considerable interest in terms of next-generation LIB host electrodes, because the unique reversible intercalation–de-intercalation process of such materials ultimately facilitates increases in LIB performance and longevity. This study explored the potential of a new class of carbon-based contorted hexabenzocoronene (c-HBC) as an anode material for high-performance LIB systems. The exploitation of the polymorphic crystalline nature of c-HBC resulted in successful development of a LIB anode based on a newly found crystal phase of trigonal R3 by solvent and subsequent thermal annealing. Our in-depth analysis based on cross-sectional transmission electron microscopy, grazing incidence X-ray diffraction, and computational investigation revealed further advantages of using contorted molecules in LIB systems. For instance, the resulting electrochemical characteristics using half-cell architecture clearly reflected single-stage Li insertion behavior associated with the large interspacing and short diffusion length of c-HBC molecule during the discharging process. In addition, the battery exhibited excellent rate capability and cycle endurance, highlighting the suitability of c-HBC as an anode material for high-performance LIBs.

  • 93. Folding Graphene Film Yields High Areal Energy Storage in Lithium-Ion Batteries ACS Nano 12, 1739–1746 (2018).

    Bin Wang, Jaegeon Ryu, Sungho Choi, Gyujin Song, Dongki Hong, Chihyun Hwang, Xiong Chen, Bo Wang, Wei Li, Hyun-Kon Song, Soojin Park* and Rodney S. Ruoff*

    We show that a high energy density can be achieved in a practical manner with freestanding electrodes without using conductive carbon, binders, and current collectors. We made and used a folded graphene composite electrode designed for a high areal capacity anode. The traditional thick graphene composite electrode, such as made by filtering graphene oxide to create a thin film and reducing it such as through chemical or thermal methods, has sluggish reaction kinetics. Instead, we have made and tested a thin composite film electrode that was folded several times using a water-assisted method; it provides a continuous electron transport path in the fold regions and introduces more channels between the folded layers, which significantly enhances the electron/ion transport kinetics. A fold electrode consisting of SnO2/graphene with high areal loading of 5 mg cm-2 has a high areal capacity of 4.15 mAh cm-2, well above commercial graphite anodes (2.50–3.50 mAh cm-2), while the thickness is maintained as low as ∼20 μm. The fold electrode shows stable cycling over 500 cycles at 1.70 mA cm-2 and improved rate capability compared to thick electrodes with the same mass loading but without folds. A full cell of fold electrode coupled with LiCoO2 cathode was assembled and delivered an areal capacity of 2.84 mAh cm-2 after 300 cycles. This folding strategy can be extended to other electrode materials and rechargeable batteries.

  • 92. Foldable Electrode Architectures Based on Silver-Nanowire-Wound or Carbon-Nanotube-Webbed Micrometer-Scale Fibers of Polyethylene Terephthalate Mats for Flexible Lithium-Ion Batteriesy Advanced Materials 30, 1705445 (2018).

    Chihyun Hwang, Woo-Jin Song, Jung-Gu Han, Sohyun Bae, Gyujin Song, Nam-Soon Choi, Soojin Park*, Hyun-Kon Song*

    A crumply and highly flexible lithium-ion battery is realized by using microfiber mat electrodes in which the microfibers are wound or webbed with conductive nanowires. This electrode architecture guarantees extraordinary mechanical durability without any increase in resistance after folding 1000 times. Its areal energy density is easily controllable by the number of folded stacks of a piece of the electrode mat. Deformable lithium-ion batteries of lithium iron phosphate as cathode and lithium titanium oxide as anode at high areal capacity (3.2 mAh cm−2) are successfully operated without structural failure and performance loss, even after repeated crumpling and folding during charging and discharging.

  • 91. Superoxide stability for reversible Na-O2 electrochemistry Scientific Reports 7, 17635 (2017).

    V. S. Dilimon, Chihyun Hwang, Yoon-Gyo Cho, Juchan Yang, Hee-Dae Lim, Kisuk Kang, Seok Ju Kang, and Hyun-Kon Song*

    Stabilizing superoxide (O2−) is one of the key issues of sodium-air batteries because the superoxide-based discharge product (NaO2) is more reversibly oxidized to oxygen when compared with peroxide (O22−) and oxide (O2−). Reversibly outstanding performances of sodium-oxygen batteries have been realized with the superoxide discharge product (NaO2) even if sodium peroxide (Na2O2) have been also known as the discharge products. Here we report that the Lewis basicity of anions of sodium salts as well as solvent molecules, both quantitatively represented by donor numbers (DNs), determines the superoxide stability and resultantly the reversibility of sodium-oxygen batteries. A DN map of superoxide stability was presented as a selection guide of salt/solvent pair. Based on sodium triflate (CF3SO3−)/dimethyl sulfoxide (DMSO) as a high-DN-pair electrolyte system, sodium ion oxygen batteries were constructed. Pre-sodiated antimony (Sb) was used as an anode during discharge instead of sodium metal because DMSO is reacted with the metal. The superoxide stability supported by the high DN anion/solvent pair (CF3SO3−/DMSO) allowed more reversible operation of the sodium ion oxygen batteries.

  • 90. A Lithium-ion Battery Using Partially Lithiated Graphite Anode and Amphi-redox LiMn2O4 Cathode Scientific Reports 7, 14879 (2017).

    Yuju Jeon, Hyun-Kuk Noh* and Hyun-Kon Song*

    Delithiation followed by lithiation of Li+-occupied (n-type) tetrahedral sites of cubic LiMn2O4 spinel (LMO) at ~4 VLi/Li+ (delivering ~100 mAh gLMO−1) has been used for energy storage by lithium ion batteries (LIBs). In this work, we utilized unoccupied (p-type) octahedral sites of LMO available for lithiation at ~3 VLi/Li+ (delivering additional ~100 mAh gLMO−1) that have never been used for LIBs in full-cell configuration. The whole capacity of amphi-redox LMO, including both oxidizable n-type and reducible p-type redox sites, at ~200 mAh gLMO−1 was realized by using the reactions both at 4 VLi/Li+ and 3 VLi/Li+. Durable reversibility of the 3 V reaction was achieved by graphene-wrapping LMO nanoparticles (LMO@Gn). Prelithiated graphite (LinC6, n 

  • 89. Graphene-wrapped Porous Sb Anodes for Sodium-Ion Batteries by Mechanochemical Compositing and Metallomechanical Reduction of Sb2O3 Electrochimica Acta 252, 25-32 (2017).

    Chihyun Hwang, Sinho Choi, Gwan Yeong Jung, Juchan Yang, Sang Kyu Kwak, Soojin Park* and Hyun-Kon Song*

    Antimony metal nanoparticles wrapped with a-few-layer graphene coat (Sb@Gn) were fabricated from their oxide form (Sb2O3) in a micrometer dimension using a novel two-step ball-milling process. The first mechanochemical process was designed to decrease the particle size of Sb2O3 microparticles for ensuring advantages of nano size and to subsequently coat the Sb2O3 nanoparticles with a-few-layer graphene (Sb2O3@Gn). The second metallomechanical ball-milling process reduced the oxide to its metal form (Sb@Gn) by the help of Zn as a metallic reductant. The graphene layer (@Gn) blocked the alloying reaction between Sb and Zn, limiting the size of Sb particles during the metallomechanical reduction step. During reduction, oxygen species were transferred from of Sb2O3 through @Gn to Zn along redox transfer pathways rather than direct mass transfer via unsaturated vacancies in the @Gn. the redox transfer involving oxidation of @Gn by O2− is plausible routes for O2− transfer in the metallomechanical reduction. The Sb@Gn anode exhibited outstanding capacity retention along charge/discharge cycles and improved rate capability in sodium-ion batteries. The @Gn provided conductive pathways to the Sb core and limited size expansion during sodium-lithium alloying.

  • 88. Bifunctional hydrous RuO2 nanocluster electrocatalyst embedded in carbon matrix for efficient and durable operation of rechargeable zinc–air batteries Scientific Reports 7, 7150 (2017).

    Han-Saem Park, Eunyong Seo, Juchan Yang, Yeongdae Lee, Byeong-Su Kim* and Hyun-Kon Song*

    Ruthenium oxide (RuO2) is the best oxygen evolution reaction (OER) electrocatalyst. Herein, we demonstrated that RuO2 can be also efficiently used as an oxygen reduction reaction (ORR) electrocatalyst, thereby serving as a bifunctional material for rechargeable Zn–air batteries. We found two forms of RuO2 (i.e. hydrous and anhydrous, respectively h-RuO2 and ah-RuO2) to show different ORR and OER electrocatalytic characteristics. Thus, h-RuO2 required large ORR overpotentials, although it completed the ORR via a 4e process. In contrast, h-RuO2 triggered the OER at lower overpotentials at the expense of showing very unstable electrocatalytic activity. To capitalize on the advantages of h-RuO2 while improving its drawbacks, we designed a unique structure (RuO2@C) where h-RuO2 nanoparticles were embedded in a carbon matrix. A double hydrophilic block copolymer-templated ruthenium precursor was transformed into RuO2 nanoparticles upon formation of the carbon matrix via annealing. The carbon matrix allowed overcoming the limitations of h-RuO2 by improving its poor conductivity and protecting the catalyst from dissolution during OER. The bifunctional RuO2@C catalyst demonstrated a very low potential gap (ΔEOER-ORR = ca. 1.0 V) at 20 mA cm−2. The Zn||RuO2@C cell showed an excellent stability (i.e. no overpotential was observed after more than 40 h).

  • 87. Curvature-Induced Metal–Support Interaction of an Islands-by-Islands Composite of Platinum Catalyst and Carbon Nano-onion for Durable Oxygen Reduction ACS Applied Materials & Interfaces 9, 23302-23308 (2017).

    Juchan Yang, Su Hwan Kim, Sang Kyu Kwak* and Hyun-Kon Song*

    Geometry of carbon supports significantly affected electrochemical durability of Pt/C (platinum electrocatalyst supported by carbon) for oxygen reduction reaction (ORR). Carbon nano-onion (CNO) was used as the support, which is characterized by its nanosize (similar to Pt size) and high curvature. Superior ORR durability was guaranteed by Pt/CNO due to (1) its islands-by-islands configuration to isolate each Pt nanoparticle from its neighbors by CNO particles; (2) highly tortuous void structure of the configuration to suppress Ostwald ripening; and (3) the curvature-induced strong interaction between CNO and Pt. The finding that highly curved carbon surface encourages electron donation to catalysts was first reported.

  • 86. Conductive and Porous Silicon Nanowire Anodes for Lithium Ion Batteries Journal of the electrochemical society 164, A1564-A1568 (2017).

    Chihyun Hwang, Kangmin Lee, Han-Don Um, Yeongdae Lee, Kwanyong Seo*, and Hyun-Kon Song*

    Silicon nanowires (SiNWs) were prepared by chemically etching silicon wafers with silver nanoparticles. Their electrical conductivities and porosities were tuned by adjusting the doping concentration of silicon wafers from which the SiNWs were prepared. Porosity of the SiNWs were proportional to doping concentrations of the mother wafer because the dopant population provides nucleation sites for etching. The electrical conductivities of the doped SiNWs were 100 times higher than those of the intrinsic SiNW. However, there was no difference in the conductivity between two different doping level SiNWs (Na = 2.7 × 1015 and 5.7 × 1019) due to the trade-off between porosity and the intrinsic conductivity of the solid backbone. The doping-dependent properties of SiNWs determined the capacity, stability and kinetics of the lithium alloying reaction of the SiNWs. The medium-level doping SiNWs, characterized by a mechanically obust porous structure, showed the most improved electrochemical performances in a full cell of a lithium manganese oxide || SiNW battery as a result of the balanced trade-off between coulombic efficiency and capacity retention.

  • 85. ZnO decorated germanium nanoparticles as anode materials in Li-ion batteries Nanotechnology 28, 095402 (2017)

    Tae-Hee Kim, Song Yi Park, Tack Ho Lee, Jaeki Jeong, Dong Suk Kim, Mark T Swihart, Hyun-Kon Song*, Jin Young Kim* and Seongbeom Kim*

    Germanium exhibits high charge capacity and high lithium diffusivity, both are the key requirements for electrode materials in high performance lithium ion batteries (LIBs). However, high volume expansion and segregation from the electrode during charge–discharge cycling have limited use of germanium in LIBs. Here, we demonstrate that ZnO decorated Ge nanoparticles (Ge@ZnO NPs) can overcome these limitations of Ge as an LIB anode material. We produced Ge NPs at high rates by laser pyrolysis of GeH4, then coated them with solution phase synthesized ZnO NPs. Half-cell tests revealed dramatically enhanced cycling stability and higher rate capability of Ge@ZnO NPs compared to Ge NPs. Enhancements arise from the core–shell structure of Ge@ZnO NPs as well as production of metallic Zn from the ZnO layer. These findings not only demonstrate a new surface treatment for Ge NPs, but also provide a new opportunity for development of high-rate LIBs.

  • 84. Coffee-Driven Green Activation of Cellulose and Its Use for All-Paper Flexible Supercapacitors ACS Applied Materials & Interfaces 9, 22568-22577 (2017).

    Donggue Lee, Yoon-Gyo Cho, Hyun-Kon Song, Sang-Jin Chun, Sang-Bum Park, Don-Ha Choi, Sun-Young Lee*, JongTae Yoo*, and Sang-Young Lee*

    Cellulose, which is one of the most abundant and renewable natural resources, has been extensively explored as an alternative substance for electrode materials such as activated carbons. Here, we demonstrate a new class of coffee-mediated green activation of cellulose as a new environmentally benign chemical activation strategy and its potential use for all-paper flexible supercapacitors. A piece of paper towel is soaked in espresso coffee (acting as a natural activating agent) and then pyrolyzed to yield paper-derived activated carbons (denoted as “EK-ACs”). Potassium ions (K+), a core ingredient of espresso, play a viable role in facilitating pyrolysis kinetics and also achieving a well-developed microporous structure in the EK-ACs. As a result, the EK-ACs show significant improvement in specific capacitance (= 131 F g−1 at a scan rate of 1.0 mV s−1) over control ACs (= 64 F g−1) obtained from the carbonization of a pristine paper towel. All-paper flexible supercapacitors are fabricated by assembling EK-ACs/carbon nanotube mixture-embedded paper towels (as electrodes), polyvinyl alcohol/KOH mixture-impregnated paper towels (as electrolytes), and polydimethylsiloxane-infiltrated paper towels (as packaging substances). The introduction of the EK-ACs (as an electrode material) and the paper towel (as a deformable/compliant substrate) enables the resulting all-paper supercapacitor to provide reliable/sustainable cell performance and also exceptional mechanical flexibility. Notably, no appreciable loss in the cell capacitance is observed after repeated bending (over 5,000 cycles) or multiple folding. The coffee-mediated green activation of cellulose and the resultant all-paper flexible supercapacitors open new material and system opportunities for eco-friendly high-performance flexible power sources.

  • 83. Mesoporous Germanium Anode Materials for Lithium-Ion Battery with Exceptional Cycling Stability in Wide Temperature Range Small 13, 1603045 (2017)

    Sinho Choi, Yoon-Gyo Cho, Jieun Kim, Nam-Soon Choi, Hyun-Kon Song, Guoxiu Wang*, Soojin Park*

    Porous structured materials have unique architectures and are promising for lithium-ion batteries to enhance performances. In particular, mesoporous materials have many advantages including a high surface area and large void spaces which can increase reactivity and accessibility of lithium ions. This study reports a synthesis of newly developed mesoporous germanium (Ge) particles prepared by a zincothermic reduction at a mild temperature for high performance lithium-ion batteries which can operate in a wide temperature range. The optimized Ge battery anodes with the mesoporous structure exhibit outstanding electrochemical properties in a wide temperature ranging from −20 to 60 °C. Ge anodes exhibit a stable cycling retention at various temperatures (capacity retention of 99% after 100 cycles at 25 °C, 84% after 300 cycles at 60 °C, and 50% after 50 cycles at −20 °C). Furthermore, full cells consisting of the mesoporous Ge anode and an LiFePO4 cathode show an excellent cyclability at −20 and 25 °C. Mesoporous Ge materials synthesized by the zincothermic reduction can be potentially applied as high performance anode materials for practical lithium-ion batteries.

  • 82. Significance of Ferroelectric Polarization in Poly(vinylidene difluoride) Binder for High-Rate Li-ion Diffusion Nano Energy 32, 255–262 (2017)

    Woo-Jin Song, Se Hun Joo, Do Hyeong Kim, Chihyun Hwang, Gwan Yeong Jung, Sohyeon Bae, Yeonguk Son, Jaephil Cho, Hyun-Kon Song, Sang Kyu Kwak*, Soojin Park*, Seok Ju Kang*

    An interesting and effective route for improving battery performance using ferroelectric poly(vinylidene difluloride) (PVDF) polymer as a binder material is demonstrated in this work. A ferroelectric PVDF phase developed under the appropriate thermal annealing process enables generation of suitable polarization on active materials during the discharge and charge process, giving rise to longer capacity with lower overpotential at a high current rate. Electrochemical analysis including in situ galvanostatic electrochemical impedance spectroscopy and a galvanostatic intermittent titration measurement revealed that the ferroelectric binder effectively reduced Li-ion diffusion resistance and supported fast migration in the vicinity of active electrodes. Computational results further support that the binding affinity of the ferroelectric PVDF surface is much higher than that of the paraelectric PVDF, confirmed by ideally formed ferroelectric and paraelectric PVDF conformations with Li-ions. Furthermore, we consistently achieved high Li-ion battery (LIB) performance in full cell architecture consisting of a LTO/separator/LFP with a ferroelectric PVDF binder in the anode and cathode materials, revealing that the polarization field is important for fabricating high-performance LIBs, potentially opening a new design concept for binder materials.

  • 81. Polypyrrole-assistant Oxygen Electrocatalysis on Perovskite Oxides Energy & Environmental Science 10, 523-527 (2017)

    Dong-Gyu Lee, Su Hwan Kim, Se Hun Joo, Ho-Il Ji, Hadi Tavassol, Yuju Jeon, Sihyuk Choi, Myeong-Hee Lee, Chanseok Kim, Sang Kyu Kwak, Guntae Kim and Hyun-Kon Song*

    Nitrogen-containing electrocatalysts such as metal-nitrogen-carbon (M-N-C) composites and nitrogen-doped carbons are known to exhibit high activities for oxygen reduction reaction (ORR). Even if the mechanism by which nitrogen improve the activities is not completely understood, strong electronic interaction between nitrogen and active sites has been found in these composites. Herein, we demonstrate a case in which nitrogen improves electroactivity, but in the absence of strong interaction with other components. The overpotentials of ORR and oxygen evolution reaction (OER) on perovskite oxide catalysts were significantly reduced simply by mixing the catalyst particles with polypyrrole/carbon composites (pPy/C). Any strong interactions between pPy (a nitrogen-containing compound) and active sites of the catalysts were not confirmed. A scenario based on the sequential role allocation between pPy and the oxide catalysts for ORR was proposed: (1) molecular oxygen is incorporated into pPy as a form of superoxide (pPy+O2-); (2) the superoxide is transferred to the active sites of perovskite catalysts; and (3) the superoxide is completely reduced along 4e ORR process.

  • 80. Carambola Shaped VO2 Nanostructures: A Binder–Free Air Electrode for Aqueous Na–Air Battery Journal of Materials Chemistry A 5, 2037-2044 (2017)

    Ziyauddin Khan, Basker SenthilKumar, Sung O Park, Seungyoung Park, Juchan Yang, Jeong Hyeon Lee, Hyun-Kon Song, Youngsik Kim, Sang Kyu Kwak* and Hyunhyub Ko*

    Binder free and bi–functional electrocatalyst plays a vital role in the development of high performance metal–air batteries. Herein, we have synthesized a vanadium oxide (VO2) nanostructure as a novel binder free and bi–functional electrocatalyst for rechargeable aqueous sodium–air (Na–air) battery. VO2 nanostructures have been grown on reduced graphene oxide coated on carbon paper which have carambola morphology. We have confirmed bi–functional nature of VO2 nanostructure by analyzing its electrocatalytic activity associated with oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The reaction pathway associated with electrocatalytic activity was also affirmed by computational modeling & simulation studies. Thereafter, aqueous Na–air cell has been built using novel binder free VO2 nanostructures as air electrode. The fabricated cell displays 0.64 V overpotential gap, 104 mW g-1 power density at 80 mA g–1 current density, 81% round trip efficiency and good cyclic stability up to 50 cycles, which are comparable to the previous best known Na-air batteries.

  • 79. A surface-reactive high-modulus binder for the reversible conversion reaction of nanoparticular cobalt oxide Electrochimica Acta 225, 78–85 (2017)

    Myeong-Hee Lee, Tae-Hee Kim, Chihyun Hwang, Jieun Kim, Hyun-Kon Song*

    Conversion-reaction-based anode materials for lithium ion batteries (LIBs) such as transition metal oxides have been considered as high-capacity alternatives to graphite. In the conversion reactions, interestingly, microparticles have been known to be superior to nanoparticles in terms of capacity retention along repeated cycles. In this work, a cross-linked two-component binder system of poly(acrylic acid) and carboxymethyl cellulose (PAA/CMC) was used for nanoparticular Co3O4. The binder was characterized by high modulus and strong bonding to the surface oxide of Co3O4. Even without carbon coating, the composite electrodes of nanoparticular Co3O4 in the presence of PAA/CMC showed significantly enhanced cycle retention with improved reversibility of the conversion reaction.

  • 78. A Metal–Organic Framework Derived Porous Cobalt Manganese Oxide Bifunctional Electrocatalyst for Hybrid Na–Air/Seawater Batteries ACS Applied Materials & Interfaces, 8, 32778-32787 (2016)

    Mari Abirami, Soo Min Hwang*, Juchan Yang, Sirugaloor Thangavel Senthilkumar, Junsoo Kim, Woo-Seok Go, Baskar Senthilkumar, Hyun-Kon Song and Youngsik Kim*

    Spinel-structured transition metal oxides are promising non-precious-metal electrocatalysts for oxygen electrocatalysis in rechargeable metal–air batteries. We applied porous cobalt manganese oxide (CMO) nanocubes as the cathode electrocatalyst in rechargeable seawater batteries, which are a hybrid-type Na–air battery with an open-structured cathode and a seawater catholyte. The porous CMO nanocubes were synthesized by the pyrolysis of a Prussian blue analogue, Mn3[Co(CN)6]2·nH2O, during air-annealing, which generated numerous pores between the final spinel-type CMO nanoparticles. The porous CMO electrocatalyst improved the redox reactions, such as the oxygen evolution/reduction reactions, at the cathode in the seawater batteries. The battery that used CMO displayed a voltage gap of ∼0.53 V, relatively small compared to that of the batteries employing commercial Pt/C (∼0.64 V) and Ir/C (∼0.73 V) nanoparticles and without any catalyst (∼1.05 V) at the initial cycle. This improved performance was due to the large surface area (catalytically active sites) and the high oxidation states of the randomly distributed Co and Mn cations in the CMO. Using a hard carbon anode, the Na-metal-free seawater battery exhibited a good cycle performance with an average discharge voltage of ∼2.7 V and a discharge capacity of ∼190 mAh g–1hard carbon during 100 cycles (energy efficiencies of 74–79%).

  • 77. Hierarchical urchin-shaped α-MnO2 on graphene-coated carbon microfibers: a binder-free electrode for rechargeable aqueous Na–air battery NPG Asia Materials 8, e294 (2016)

    Ziyauddin Khan, Seungyoung Park, Soo Min Hwang, Juchan Yang, Youngsu Lee, Hyun-Kon Song, Youngsik Kim* and Hyunhyub Ko*

    With the increasing demand of cost-effective and high-energy devices, sodium–air (Na–air) batteries have attracted immense interest due to the natural abundance of sodium in contrast to lithium. In particular, an aqueous Na–air battery has fundamental advantage over non-aqueous batteries due to the formation of highly water-soluble discharge product, which improve the overall performance of the system in terms of energy density, cyclic stability and round-trip efficiency. Despite these advantages, the rechargeability of aqueous Na–air batteries has not yet been demonstrated when using non-precious metal catalysts. In this work, we rationally synthesized a binder-free and robust electrode by directly growing urchin-shaped MnO2 nanowires on porous reduced graphene oxide-coated carbon microfiber (MGC) mats and fabricated an aqueous Na–air cell using the MGC as an air electrode to demonstrate the rechargeability of an aqueous Na–air battery. The fabricated aqueous Na–air cell exhibited excellent rechargeability and rate capability with a low overpotential gap (0.7 V) and high round-trip efficiency (81%). We believe that our approach opens a new avenue for synthesizing robust and binder-free electrodes that can be utilized to build not only metal–air batteries but also other energy systems such as supercapacitors, metal–ion batteries and fuel cells.

  • 76. Design of an ultra-durable silicon-based battery anode material with exceptional high-temperature cycling stability Nano Energy, 26, 192-199 (2016)

    Hyungmin Park, Sinho Choi, Sung-Jun Lee, Yoon-Gyo Cho, Gaeun Hwang, Hyun-Kon Song, Nam-Soon Choi, Soojin Park*

    A new class of Si-based materials is fabricated by synergistic coupling of amorphous ABOx and carbon coating layers onto Si particles. In this system, ABOx stabilizes the SEI layers, while carbon acts as an electrical conducting material. The resulting Si-based anodes exhibit high specific capacities (1667 mA h g−1 (25 °C) and 2021 mA h g−1 (60 °C) at 1 C rate) and highly stable cycling performances (capacity retention of 60% after 500 cycles at 25 °C and 64% after 600 cycles at 60 °C).

  • 75. Organogel electrolyte for high-loading silicon batteries Journal of Material Chemistry A 4, 8005-8009 (2016)

    Yoon-Gyo Cho, Hyungmin Park, Jung-In Lee, Chihyun Hwang, Yuju Jeon, Soojin Park and Hyun-Kon Song*

    A cyanoresin organogel electrolyte, characterized by in situ gelation with no initiators or crosslinkers, was used for high-loading silicon batteries of 1.3 mgSi cm−2 (equivalent to 3.3 mA h cm−2). The organogel provided additional cohesion between the silicon particles and maintained electrode integrity even after pulverization, completely suppressing severe crack development and serious electrode thickness changes observed in liquid electrolytes. The capacity retention upon cycling was significantly improved in the organogel when compared with its liquid counterpart.

  • 74. Enhancing Interfacial Bonding between Anisotropically Oriented Grains Using a Glue-Nanofiller for Advanced Li-Ion Battery Cathode Advanced Materials 28, 4705-4712 (2016)

    Hyejung Kim, Sanghan Lee, Hyeon Cho, Junhyeok Kim, Jieun Lee, Suhyeon Park, Se Hun Joo, Su Hwan Kim, Yoon-Gyo Cho, Hyun-Kon Song, Sang Kyu Kwak*, Jaephil Cho*

    Formation of a glue-nanofiller layer between grains, consisting of a middle-temperature spinel-like LixCoO2 phase, reinforces the strength of the incoherent interfacial binding between anisotropically oriented grains by enhancing the face-to-face adhesion strength. The cathode treated with the glue-layer exhibits steady cycling performance at both room-temperature and 60 °C. These results represent a step forward in advanced lithium-ion battery via simple cathode coating.

  • 73. Investigation on silicon alloying kinetics during lithiation by galvanostatic impedance spectroscopy Journal of Power Sources 315, 145–151 (2016)

    Younghoon Ko, Chihyun Hwang, Hyun-Kon Song*

    Electrochemical parameters characterizing lithiation processes in silicon anodes of lithium ion batteries (LIBs) were measured in situ during a practical charging operation by galvanostatic electrochemical impedance spectroscopy (GS-EIS).

  • 72. Dependency of electrochemical performances of silicon lithium ion batteries on glycosidic linkages of polysaccharide binders ACS Applied Materials & Interfaces 8, 4042–4047 (2016)

    Da-Eun Yoon, Chihyun Hwang*, Na-Ri Kang, Ungju Lee, Dongjoon Ahn, Ju-Young Kim, Hyun-Kon Song*

    Molecular structures of polysaccharide binders determining mechanical properties were correlated to electrochemical performances of silicon anodes for lithium ion batteries. Glycosidic linkages (α and β) and side chains (-COOH and -OH) were selected and proven as the major factors of the molecular structures. Three different single-component polysaccharides were compared: pectin for α-linkages versus carboxylic methyl cellulose (CMC) for β-linkages from the linkage’s standpoint; and pectin as a COOH-containing polymer and amylose as its non-COOH counterpart from the side chain’s standpoint. Pectin was remarkably superior to CMC and amylose in cyclability and rate capability of battery cells based on silicon anodes. The pectin binder allowed volume expansion of silicon electrodes with keeping high porosity during lithiation due to the elastic nature caused by the chair-to-boat conformation in α-linkages of its backbone. Physical integrity of pectin-based electrodes was not challenged during repeated lithiation/delithiation cycles without crack development that was observed in rigid CMC-based electrodes. Covalent bonds formed between carboxylic side chains of pectin and silicon surface oxide prevented active silicon mass from being detached away from electric pathways. However, hydrogen bonds between hydroxyl side chains of amylose and silicon surface oxide were not strong enough to keep silicon mass electrochemically active after cyclability tests.

  • 71. Conductivity-Dependent Completion of Oxygen Reduction on Oxide Catalysts Angewandte Chemie International Edition 54, 15730-15733 (2015)

    Dong-Gyu Lee, Ohhun Gwon, Han-Saem Park, Su Hwan Kim, Juchan Yang, Sang Kyu Kwak, Guntae Kim*, Hyun-Kon Song*

    Conductivity makes the difference: Conductive environments surrounding active sites, achieved by more conductive perovskite catalysts (BSCFO, NBSCO) or higher carbon contents, result in a higher number of electrons transferred during complete four-electron (4e) reduction of oxygen, changing the rate-determining step from a two-step 2e process to a single-step 1e process.

  • 70. Breathing silicon anodes for durable high-power operations Scientific Reports 5, 14433 (2015)

    Chihyun Hwang, Sehun Joo, Na-Ri Kang, Ungju Lee, Tae-Hee Kim, Yuju Jeon, Jieun Kim, Young-Jin Kim, Ju-Young Kim,* Sang-Kyu Kwak* & Hyun-Kon Song*

    Silicon anode materials have been developed to achieve high capacity lithium ion batteries for operating smart phones and driving electric vehicles for longer time. Serious volume expansion induced by lithiation, which is the main drawback of silicon, has been challenged by multi-faceted approaches. Mechanically rigid and stiff polymers (e.g. alginate and carboxymethyl cellulose) were considered as the good choices of binders for silicon because they grab silicon particles in a tight and rigid way so that pulverization and then break-away of the active mass from electric pathways are suppressed. Contrary to the public wisdom, in this work, we demonstrate that electrochemical performances are secured better by letting silicon electrodes breathe in and out lithium ions with volume change rather than by fixing their dimensions. The breathing electrodes were achieved by using a polysaccharide (pullulan), the conformation of which is modulated from chair to boat during elongation. The conformational transition of pullulan was originated from its α glycosidic linkages while the conventional rigid polysaccharide binders have β linkages.

  • 69. Selectively accelerated Li+ transport to Si anodes via an organogel binder J. Power Sources 298, 8–13 (2015)

    Chihyun Hwang, Yoon-Gyo Cho, Na-Ri Kang, Younghoon Ko, Ungju Lee, Dongjoon Ahn, Ju-Young Kim, Young-Jin Kim and Hyun-Kon Song*

    Silicon, a promising high-capacity anode material of lithium ion batteries, suffers from its volume expansion leading to pulverization and low conductivities, showing capacity decay during cycling and low capacities at fast charging and discharging. In addition to popular active-material-modifying strategies, building lithium-ion-rich environments around silicon surface is helpful in enhancing unsatisfactory performances of silicon anodes. In this work, we accelerated lithium ion transport to silicon surface by using an organogel binder to utilize the electroactivity of silicon in a more efficient way. The cyanoethyl polymer (PVA-CN), characterized by high lithium ion transference number as well as appropriate elastic modulus with strong adhesion, enhanced cycle stability of silicon anodes with high coulombic efficiency even at high temperature (60 oC) as well as at fast charging/discharging rates.

  • 68. High-performance silicon-based multicomponent battery anodes produced via synergistic coupling of multifunctional coating layers Energy & Environmental Science 8, 2075-2084 (2015)

    Jung-In Lee, Younghoon Ko, Myoungsoo Shin, Hyun-Kon Song, Nam-Soon Choi, Min Gyu Kim* and Soojin Park*

    Nanostructured Si-based materials are key building blocks for next-generation energy storage devices. To meet the requirements of practical energy storage devices, Si-based materials should exhibit high-power, low volume change, and high tap density. So far, there have been no reliable materials reported satisfying all of these requirements. Here, we report a novel Si-based multicomponent design, in which the Si core is covered with multifunctional shell layers. The synergistic coupling of Si with the multifunctional shell provides vital clues for satisfying all Si anode requirements for practical batteries. The Si-based multicomponent anode delivers a high capacity of [similar]1000 mA h g−1, a highly stable cycling retention ([similar]65% after 1000 cycles at 1 C), an excellent rate capability ([similar]800 mA h g−1 at 10 C), and a remarkably suppressed volume expansion (12% after 100 cycles). Our synthetic process is simple, low-cost, and safe, facilitating new methods for developing electrode materials for practical energy storage.

  • 67. All-in-one assembly based on 3D-intertangled and cross-jointed architectures of Si/Cu 1D-nanowires for lithium ion batteries Scientific Reports 5, 8623 (2015)

    Chihyun Hwang, Tae-Hee Kim, Yoon-Gyo Cho, Jieun Kim and Hyun-Kon Song*

    All-in-one assemblies of separator, electrode and current collector (SECA) for lithium ion batteries are presented by using 1D nanowires of Si and Cu (nwSi and nwCu). Even without binders, integrity of SECA is secured via structural joints based on ductility of Cu as well as entanglement of nwSi and nwCu. By controlling the ratio of the nanowires, the number of contact points and voids accommodating volume expansion of Si active material are tunable. Zero volume expansion and high energy density are simultaneously achievable by the architecture.

  • 66. Multiple roles of superoxide on oxygen reduction reaction in Li+-containing non-aqueous electrolyte: Contribution to formation of oxide as well as peroxide The Journal of Physical Chemistry C 119, 3472–3480 (2015)

    V. S. Dilimon, Dong-Gyu Lee, Sung-Dae Yim and Hyun-Kon Song*

    Understanding Li-O2 electrochemistry without ambiguities is the basis required for achieving high energy density with efficient cycling for lithi-um-air batteries. Oxygen reduction reaction (ORR) on carbon is supposed to proceed via a three step mechanism: oxygen (O20) to superoxide (O2- or LiO2) to peroxide (O22- or Li2O2) to oxide (O2- or Li2O). In this work, we provide clear evidences relevant to three controversial issues: (1) whether the superoxide intermediate is really formed; (2) whether the superoxide exists for a significant time period or they are immediately con-verted to the peroxide species; and (3) whether conversion of peroxide to oxide is feasible or the final discharge product of ORR is not oxide but peroxide. ORR on carbon electrode with LiClO4 or LiPF6 in dimethyl sulfoxide (DMSO) as an electrolyte was used as a model system. In addi-tion to conventional voltammetry and Raman spectroscopy, the staircase cyclic voltammetry combined with Fourier transform electrochemical impedance spectroscopy (SCV-FTEIS) was used to investigate the Li-O2 electrochemistry in situ during potential scans. Molecular oxygen was quasi-reversibly reduced to superoxide in the first step. The superoxide was stable enough to be detected in the electrolytes. The superoxide was reduced to peroxide that existed as a surface-adsorbed species. Reduction proceeded further to produce oxide as its final product. Also, Li2CO3 formation resulting from electrolyte decomposition/electrode corrosion was observed only with LiClO4. In addition, we identified a novel chemical route for the oxide formation occurring even at not-enough overpotential: peroxide is further reduced to oxide by the help of superoxide as an in situ formed one-electron reducing agent. This report gives a clear picture of the ORR mechanism on carbon electrode in Li+-containing non-aqueous electrolyte by providing evidences for the formation of superoxide intermediate and oxide for the first time.

  • 65. Highly Porous Piezoelectric PVDF Membrane as Effective Lithium Ion Transfer Channels for Enhanced Self-Charging Power Cell Nano Energy 14, 77-86 (2015)

    Young-Soo Kim, Yannan Xie, Xiaonan Wen, Sihong Wang, Sang Jae Kim, Hyun-Kon Song* and Zhong Lin Wang*

    A self-charging power cell (SCPC) is a structure that hybridizes the mechanisms for energy conversion and storage into one process through which mechanical energy can be directly converted into electrochemical energy. A key structure of an SCPC is the use of a polyvinylidene fluoride (PVDF) piezo-separator. Herein, we have fabricated a piezoelectric β-form PVDF separator with a highly porous architecture by introducing ZnO particles. The electrochemical charge/discharge performance of this SCPC was greatly enhanced at lower discharge rates compared to highly stretched (high-β-content) or less porous PVDF membranes. The lower charge-transfer resistance of this well-developed porous piezo-separator is the main factor that facilitated the transport of Li+ ions without sacrificing piezoelectric performance. This study reveals a novel approach for improving the performance of SCPCs.

  • 64. General Approach for High-Power Li-Ion Batteries: Multiscale Lithographic Patterning of Electrodes ChemSusChem 7, 3483-3490 (2014)

    Sinho Choi†, Tae-Hee Kim†, Jung-In Lee, Jieun Kim, Hyun-Kon Song*, Soojin Park*

    We demonstrate multiscale patterned electrodes that provide surface-area enhancement and strong adhesion between electrode materials and current collector. The combination of multiscale structured current collector and active materials (anodes and cathodes) enables us to make high-performance Li-ion batteries (LIBs). When LiFePO4 (LFP) cathode and Li4Ti5O12 (LTO) anode materials are combined with patterned current collectors, their electrochemical performances are significantly improved, including a high rate capability (LiFePO4: 100 mAh g−1, Li4Ti5O12: 60 mAh g−1 at 100C rate) and highly stable cycling (LiFePO4: capacity retention of 99.8 % after 50 cycles at 10C rate). Moreover, we successfully fabricate full cell system consisting of patterned LFP cathode and patterned LTO anode, exhibiting high-power battery performances [capacity of approximately 70 mAh g−1 during 1000 cycles at 10C rate (corresponding to charging/discharging time of 6 min)]. We extend this idea to Si anode that exhibits a large volume change during lithiation/delithiation process. The patterned Si electrodes show significantly enhanced electrochemical performances, including a high specific capacity (825 mAh g−1) at high rate of 5C and a stable cycling retention (88 % after 100 cycle at a 0.1C rate). This simple strategy can be extended to other cathode and anode materials for practical LIB applications.

  • 63. High-yield synthesis of single-crystal silicon nanoparticles as anode materials of lithium ion batteries via photosensitizer-assisted laser pyrolysis Journal of Materials Chemistry A 2, 18070-18075 (2014)

    Seongbeom Kim, Chihyun Hwang, Song Yi Park, Seo-Jin Ko, Hyungmin Park, Won Chul Choi, Jong Bok Kim, Dong Suk Kim, Soojin Park, Jin Young Kim* and Hyun-Kon Song*

    Single crystal silicon nanoparticles (Si-NPs) of 20 nm were produced via laser pyrolysis with a virtually complete conversion from SiH4 to Si-NPs. SF6 was used as the photosensitizer to transfer laser beam energy to silicon precursors, dramatically enhancing crystallinity of Si-NPs and their production efficiency. By using their well-developed crystalline structure, the directional volume expansion of Si-NPs was confirmed during lithiation. Lithiation/delithiation kinetics of our Si-NPs was superior to that of their amorphous counterparts due to the footprinted Li+ pathways formed during amorphization.

  • 62. LiFePO4 Nanostructures Fabricated from Iron(III) Phosphate (FePO4 · 2H2O) by Hydrothermal Method J. Nanoscience Nanotechnology 15, 734-741 (2015)

    Viswanathan S. Saji and Hyun-Kon Song

    Electrode materials having nanometer scale dimensions are expected to have property enhancements due to enhanced surface area and mass/charge transport kinetics. This is particularly relevant to intrinsically low electronically conductive materials such as lithium iron phosphate (LiFePO4), which is of recent research interest as a high performance intercalation electrode material for Liion batteries. Many of the reported works on LiFePO4 synthesis are unattractive either due to the high cost of raw materials or due to the complex synthesis technique. In this direction, synthesis of LiFePO4 directly from inexpensive FePO4 shows promise. The present study reports LiFePO4 nanostructures prepared from iron (III) phosphate (FePO4 ·2H2O) by precipitation-hydrothermal method. The sintered powder was characterized by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), Inductive coupled plasma-optical emission spectroscopy (ICP-OES), and Electron microscopy (SEM and TEM). Two synthesis methods, viz. bulk synthesis and anodized aluminum oxide (AAO) template-assisted synthesis are reported. By bulk synthesis, micro-sized particles having peculiar surface nanostructuring were formed at precipitation pH of 6.0 to 7.5 whereas typical nanosized LiFePO4 resulted at pH ≥8.0. An in-situ precipitation strategy inside the pores of AAO utilizing the spin coating was utilized for the AAO-template-assisted synthesis. The template with pores filled with the precipitate was subsequently subjected to hydrothermal process and high temperature sintering to fabricate compact rod-like structures.

  • 61. Synthesis of a Redox-Active Denpol as a Potential Electrode in Rechargeable Organic Batteries ChemElectroChem 1, 1618–1622 (2014)

    Jonggi Kim, Jieun Kim, Jungho Lee, Hyun-Kon Song* and Changduk Yang*

    Together with ROMP strategy, a controlled protocol of a progressive addition of the ultrafast-initiating and more reactive third generation Grubbs catalyst yields a denpol containing multi-anthraquinone (AQ)-terminated dendrons (AQ-ter-Denpol) (Mn = 14.0 kDa) with a unimodal molar mass distribution (PDI = 1.20), fully characterized by 1H NMR. AQ-ter-denpol is investigated as a novel organic cathode material for rechargeable Li-ion batteries with a view to its unique morphology. Our methodologies herein reported establish an opportunity for developing a new generation of organic electrodes based on denpols.

  • 60. Preparation of Co3O4 electrode materials with different microstructures via pseudomorphic conversion of Co-based metal-organic frameworks Journal of Materials Chemistry A 2, 14393-14400 (2014)

    Kyung Joo Lee, Tae-Hee Kim, Tae Kyung Kim, Jae Hwa Lee, Hyun-Kon Song* and Hoi Ri Moon*

    To develop high-performance nanostructured metal oxide electrodes, it is important to understand the structural effects on electrochemical performances. Thus, the preparation of metal oxide materials which have well-tailored nanostructures is crucial for the studies. However, while the synthetic strategies to control the size of metal oxide nanoparticles are well-developed, the control of those higher level structures, namely microstructure, is not established very well. Herein, we present the synthesis of two kinds of Co3O4 nanomaterials through pseudomorphic conversion that the macroscopic morphologies of parent MOFs such as plate-like and rod-like shape were well-maintained. Both Co3O4 nanomaterials are composed of almost identical 10 nm-sized primary nanocrystals, but those nanoporous secondary structures and macroscopic morphologies such as plate and rod shapes are different. Those Co3O4 nanomaterials were utilized as an electrode of lithium ion batteries (LIBs), and their electrochemical properties were comparatively studied. It was revealed that the different cyclability and rate capability are attributed to their different microstructures. Pseudo-monolithic integration of the primary and secondary structures at higher level was the governing factor to determine the electrochemical performances of the Co3O4.

  • 59. Conducting polymer-skinned electroactive materials of lithium ion batteries: Ready for mono-component electrodes without additional binders and conductive agents ACS Applied Materials & Interface 6, 12789–12797 (2014)

    Ju-Myung Kim, Han-Saem Park, Jang-Hoon Park, Tae-Hee Kim, Hyun-Kon Song* and Sang-Young Lee*

    Rapid growth of mobile and even wearable electronics is in pursuit of high-energy density lithium-ion batteries. One simple and facile way to achieve this goal is the elimination of non-electroactive components of electrodes such as binders and conductive agents. Here, we present a new concept of mono-component electrodes comprising solely electroactive materials that are wrapped with an insignificant amount (less than 0.4 wt.%) of conducting polymer (PEDOT:PSS or poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate)). The PEDOT:PSS as ultra-skinny surface layer on electroactive materials (LiCoO2 (LCO) powders are chosen as a model system to explore feasibility of this new concept) successfully acts as a kind of binder as well as mixed (both electrically and ionically) conductive film, playing a key role in enabling the mono-component electrode. The electric conductivity of mono-component LCO cathode is controlled by simply varying PSS content and also structural conformation (benzoid-favoring coil strucutre and quinoid-favoring linear or extended coil structure) of PEDOT in the PEDOT:PSS skin. Notably, substantial increase in mass-loading density of LCO cathode is realized with the PEDOT:PSS skin without sacrificing electronic/ionic transport pathways. We envisage that the PEDOT:PSS-skinned electrode strategy opens a scalable and versatile route for making practically meaningful binder-/conductive agent-free (mono-component) electrodes.

  • 58. Surface Complex Formation between Aliphatic Nitrile Molecules and Transition Metal Atoms for Thermally Stable Lithium Ion Batteries ACS Applied Materials & Interface 6, 8913–8920 (2014)

    Young-Soo Kim, Hochun Lee, Hyun-Kon Song*

    Non-flammability of electrolyte and tolerance of cells against thermal abuse should be guaranteed for widespread applications of lithium-ion batteries (LIBs). As a strategy to improve thermal stability of LIBs, here, we report on nitrile-based molecular coverage on surface of cathode active materials to block or suppress thermally-accelerated side reactions between electrode and electrolyte. Two different series of aliphatic nitriles were introduced as an additive into a carbonate-based electrolyte: di-nitriles (CN-[CH2]n-CN with n = 2, 5 and 10) and mono-nitriles (CH3-[CH2]m-CN with m = 2, 5 and 10). On the basis of the strong interaction between the electronegativity of nitrile functional groups and the electropositivity of cobalt in LiCoO2 cathode, aliphatic mono- and di-nitrile molecules improved the thermal stability of lithium ion cells by efficiently protecting the surface of LiCoO2. Three factors, the surface coverage , the steric hindrance of aliphatic moiety within nitrile molecule and the chain polarity, mainly affect thermal tolerance as well as cell performances at elevated temperature.

  • 57. Programming galvanostatic rates for fast-charging lithium ion batteries: a graphite case RSC Advances 4, 16545-16550 (2014)

    Younghoon Ko, Yoon-Gyo Cho, Hyun-Kon Song*

    Galvanostatically induced lithiation of graphite, as a cathodic process of lithium ion batteries during charging, was investigated in situ by galvanostatic electrochemical impedance spectroscopy (GS-EIS). When lithiation is driven by charge rates slow enough for kinetics of the lithiation process to be considered relatively sluggish, charge transfer resistance (RCT) is slightly reduced as lithium ion intercalation proceeds from the dilute stage to stage 2L. Subsequently, RCT begins to increase during transformation of stage 2L to stage 2, followed by an abrupt increase in RCT observed during transition from stage 2 to stage 1, or after the inter-space of graphites is fully filled with lithium ions. As the ratio of charge rate to lithiated graphite increases, the potential responsible for the transition from stage 2L to stage 2 is shifted to more negative values due to significant polarization. Simultaneously, cells reach cut-off potentials before the transition from stage 2 to stage 1 proceeds. Based on the information regarding RCT profiles obtained by galvanostatic charging processes, a charging strategy is programmed with several different charge rates (C-rates). The capacity of lithiation is significantly enhanced by a C-rate switching (CRS) strategy. As a representative example, 75% of available capacity is charged for 50 minutes by a combination of 2 C, 1 C, and 0.5 C. However, only 12% and 51% of graphite is lithiated within the same time duration by a single charge rate of 0.1 C and 0.5 C, respectively.

  • 56. Enlarging d-spacing of graphite and polarizing its surface charge for driving lithium ions fast Journal of Materials Chemistry A 2, 7600-7605 (2014)

    Tae-Hee Kim, Eun Kyung Jeon, Younghoon Ko, Bo Yun Jang, Byeong-Su Kim,* and Hyun-Kon Song*

    Lithium ion transport was accelerated within graphites by controlling its d-spacing as well as its functional groups. By oxidizing bare graphite in a mild condition, expanded graphites (EG* where * = functional groups) were obtained with increasing d-spacing from 0.3359 nm to 0.3395 nm as well as with functional groups formed on the plane or at the edges of graphites. The subsequent thermal reduction of EG* led to insignificant change of d-spacing (0.3390 nm), simultaneously eliminating a portion of the functional groups (EG). The enlargement of d-spacing reduced kinetic hindrance of lithium ion movement within the expanded graphites (EG* and EG) by reserving more space for ionic transport route. In addition, the activation energy of lithium ion intercalation in EG* was reduced by surface charge polarization of graphites induced by hydrogen bonds between oxygen atoms of carbonates in electrolytes and hydrogen atoms of surface functional groups of the expanded graphites, even if degree of graphitization decreased. Re-graphitization induced by the subsequent thermal reduction increased delithiation capacities (QdLi) of EG as an anode for lithium ion batteries especially at high currents: QdLi at 50C = 243 mAh g-1 for EG versus 66 mAh g-1 for bare graphite.

  • 55. Doubling Capacity of Lithium Manganese Oxide Spinel via Flexible Skinny Graphitic Layer Angewandte Chemie International Edition 53, 5059–5063 (2014)

    Hyun Kuk Noh,* Han-Saem Park, Hu Young Jeong, Sang Uck Lee, and Hyun-Kon Song*

    By coating nanoparticular lithium manganese oxide (LMO) spinel with a few layers of graphitic basal planes, the capacity of the material reached up to 220 mA h g−1 at a cutoff voltage of 2.5 V. The graphitic layers 1) provided a facile electron-transfer highway without hindering ion access and, more interestingly, 2) stabilized the structural distortion at the 3 V region reaction. The gain was won by a simple method in which microsized LMO was ball-milled in the presence of graphite with high energy. Vibratory ball milling pulverized the LMO into the nanoscale, exfoliated graphite of less than 10 layers and combined them together with an extremely intimate contact. Ab initio calculations show that the intrinsically very low electrical conductivity of the tetragonal phase of the LMO is responsible for the poor electrochemical performance in the 3 V region and could be overcome by the graphitic skin strategy proposed.

  • 54. Nitrile-assistant eutectic electrolytes for cryogenic operation of lithium ion batteries at fast charges and discharges Energy & Environmental Science 7, 1737-1743 (2014)

    Yoon-Gyo Cho, Young-Soo Kim, Dong-Gil Sung, Myung-Su Seo, Hyun-Kon Song*

    The charge/discharge characteristics at low temperature (LT = -20 oC) are enhanced by using ethylene carbonate (EC)-based electrolytes with the help of assistant solvents of nitriles. Conventional liquid electrolytes (e.g. a mixture of EC and dimethyl carbonate (DMC), abbreviated by LD) cannot support satisfactory capacity at the low temperature as well as high rates even if electric vehicles require low temperature operation. Introducing propionitrile or butyronitrile (Pn or Bn) into LD (resulting in LDPn or LDBn) as a co-solvent increases significantly the high-rate capacities at -20 oC. For example, LDPn delivers 62 % of available capacity at 1C and 46 % at 3C with 2.7 V cut-off while the control LD provides just 6 % and 4 % at the same rates. The successful operation at -20 oC with the nitrile-assistant electrolytes results from high ionic conductivity, low viscosity and freezing point depression caused by eutectic behavior of carbonates (EC/DMC) and Pn. Based on phase diagram of Pn with EC/DMC, we expect meaningful battery operation up to -110 oC at the eutectic composition with 18 % Pn in 1:1 EC/DMC.

  • 53. Succinonitrile as a Corrosion Inhibitor of Copper Current Collectors for Overdischarge Protection of Lithium Ion Batteries ACS Appl. Mater. Interfaces 6, 2039-2043 (2014)

    Young-Soo Kim, Seon-Ha Lee, Mi-Young Son, Young Mee Jung, Hyun-Kon Song*, and Hochun Lee*

    Succinonitrile (SN) is investigated as an electrolyte additive for copper corrosion inhibition to provide overdischarge (OD) protection to lithium ion batteries (LIBs). The anodic Cu corrosion, occurring above 3.5 V (vs Li/Li+) in conventional LIB electrolytes, is suppressed until a voltage of 4.5 V is reached in the presence of SN. The corrosion inhibition by SN is ascribed to the formation of an SN-induced passive layer, which spontaneously develops on the copper surface during the first anodic scan. The passive layer is composed mainly of Cu(SN)2PF6 units, which is evidenced by Raman spectroscopy and electrochemical quartz crystal microbalance measurements. The effects of the SN additive on OD protection are confirmed by using 750 mAh pouch-type full cells of LiCoO2 and graphite with lithium metal as a reference electrode. Addition of SN completely prevents corrosion of the copper current collector in the full cell configuration, thereby tuning the LIB chemistry to be inherently immune to the OD abuses.

  • 52. An inter-tangled network of redox-active and conducting polymers as a cathode for ultrafast rechargeable batteries Phys. Chem. Chem. Phys. 16, 5295-5300 (2014)

    Jieun Kim, Han-Saem Park, Tae-Hee Kim, Sung Yeol Kim, Hyun-Kon Song*

    An 1D organic redox-active material is composited with another 1D conductive material for rechargeable batteries. Poly(vinyl carbazole) (or PVK) and Poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (or PEDOT:PSS) are used as the redox-active and conductive 1D materials, respectively. Due to their extreme anisotropic geometry, the two polymers are expected to be inter-tangled with each other, showing an kinetically ideal model system in which each redox-active moiety of PVK is supposed to be directly connected with the conducting pathways of PEDOT:PSS. In addition to the role of conductive agents providing kinetic benefits, PEDOT:PSS works as an efficient binder that guarantees enhanced electrochemical performances with only a tenth of the amount of a conventional binder (polyvinylidene fluoride or PVdF). The benefit of gravimetric energy density gain obtained with the conductive binder comes mainly from efficient spatial coverage of binding volume due to the low density of PEDOT:PSS. Towards realizing flexible all-polymer batteries, a quasi-all-polymer battery half cell is designed with the PVK/ PEDOT:PSS composite with a polymer gel electrolyte.

  • 51. Study on the Electrochemical Kinetics of Manganese Dioxide/Multiwall Carbon Nanotube Composite by Voltammetric Charge Analysis J. Electrochem. Soc. 161, A137-A141 (2014)

    Seung-Beom Yoon, Hyun-Kon Song, Kwang Chul Roh,* Kwang-Bum Kim*

    Electrochemical properties of MnO2/multiwall carbon nanotube (MWCNT) composites were investigated by using cavity microelectrodes (CME). Electrochemical kinetics of the MnO2/MWCNT composites were studied by analyzing the scan rate dependence of voltammetric charge, which was measured by cyclic voltammetry (CV) at various scan rates ranging from 20 mV s−1 to 1000 mV s−1. Based on several mathematical models, the relationship between voltammetric charge and scan rate was interpreted systematically. At slow scan rates, ion diffusion in MnO2 dominantly determined the rate of the overall electrochemical process. However, the faradaic reaction of Mn3+/Mn4+ at the MnO2 surface competed with mass transfer in terms of kinetics when the potential scan rate was higher than 400 mV s−1

  • 50. Kinetically enhanced pseudocapacitance of conducting polymer doped with reduced graphene oxide through a miscible electron transfer interface Nano Energy 3, 1-9 (2014)

    Han-Saem Park, Myeong-Hee Lee, Ryeo Yun Hwang, Ok-Kyung Park, Kiyoung Jo, Taemin Lee, Byeong-Su Kim*, Hyun-Kon Song*

    Herein, we report on electrochemical doping of a conducting polymer (CP) with anionically modified graphene nanosheets. The architecture built from reduced graphene oxide (rGO) skeleton skinned by polypyrrole (pPy) enhanced supercapacitor performances especially at high discharge rates superior to those of the same CP with a conventional dopant: e.g., from 141 to 280 F g−1 at 1000C equivalent to ~50 A g−1. At relatively low rates, the graphene-doped pPy reached the theoretical capacitance of pPy, indicating efficient use of whole electroactive mass.

  • 49. Redox-active charge carriers of conducting polymers as a tuner of conductivity and its potential window Scientific Reports 3, 2454 (2013)

    Han-Saem Park, Seo-Jin Ko, Jeong-Seok Park, Jin Young Kim and Hyun-Kon Song*

    Electric conductivity of conducting polymers has been steadily enhanced towards a level worthy of being called its alias, “synthetic metal”. PEDOT:PSS (poly(3,4-ethylenedioxy thiophene) doped with poly(styrene sulfonate)), as a representative conducting polymer, recently reached around 3,000 S cm−1, the value to open the possibility to replace transparent conductive oxides. The leading strategy to drive the conductivity increase is solvent annealing in which aqueous solution of PEDOT:PSS is treated with an assistant solvent such as DMSO (dimethyl sulfoxide). In addition to the conductivity enhancement, we found that the potential range in which PEDOT:PSS is conductive is tuned wider into a negative potential direction by the DMSO-annealing. Also, the increase in a redox-active fraction of charge carriers is proposed to be responsible for the enhancement of conductivity in the solvent annealing process.

  • 48. A physical organogel electrolyte: characterized by in situ thermo-irreversible gelation and single-ion-predominent conduction Scientific Reports 3, 1917 (2013)

    Young-Soo Kim, Yoon-Gyo Cho, Dorj Odkhuu, Noejung Park* and Hyun-Kon Song*

    Electrolytes are characterized by their ionic conductivity (σi). It is desirable that overall σi results from the dominant contribution of the ions of interest (e.g. Li+ in lithium ion batteries or LIB). However, high values of cationic transference number (t+) achieved by solid or gel electrolytes have resulted in low σi leading to inferior cell performances. Here we present an organogel polymer electrolyte characterized by a high liquid-electrolyte-level σi (~101 mS cm-1) with high t+ of Li+ (> 0.8) for LIB. A conventional liquid electrolyte in presence of a cyano resin was physically and irreversibly gelated at 60 oC without any initiators and crosslinkers, showing the behavior of lower critical solution temperature. During gelation, σi of the electrolyte followed a typical Arrhenius-type temperature dependency, even if its viscosity increased dramatically with temperature. Based on the Li+-driven ion conduction, LIB using the organogel electrolyte delivered significantly enhanced cyclability and thermal stability.

  • 47. Hollow versus nonhollow: the electrochemical preference in a case study of the conversion reaction of Fe3O4 Electrochimica Acta 105, 47-52 (2013)

    Tae-Hee Kim and Hyun-Kon Song*

    Hollow sphere geometry is compared with the corresponding nonhollow one in terms of its electrochemical benefits. Lithiation of Fe3O4 and its backward reaction is chosen as a case study process. Dimension of the hollow structure is carefully controlled to have the same mass per a single particle as that of its nonhollow counterpart. The comparison shows the possibility that the faradaic performances of hollow geometry could be better than those of the nonhollow in terms of volumetric as well as gravimetric capacities, even if the hollow has void in its centre.

  • 46. Facile Route to an Efficient NiO Supercapacitor with a Three-Dimensional Nanonetwork Morphology ACS Applied Materials & Interfaces 5, 1596-1603 (2013)

    Sun-I Kim, Jung-Soo Lee, Hyo-Jin Ahn, Hyun-Kon Song, Ji-Hyun Jang*

    NiO nanostructures with three distinct morphologies were fabricated by a sol–gel method and their morphology-dependent supercapacitor properties were exploited. The nanoflower- shaped NiO with a distinctive three-dimensional (3D) network and the highest pore volume shows the best supercapacitor properties. The nanopores in flower-shaped nanostructures, offering advantages in contact with and transport of the electrolyte, allow for 3D nanochannels in NiO structure, providing longer electron pathways. The XPS and EIS data of the NiO nanostructure confirm that the flower-shaped NiO, which has the lowest surface area among the three morphologies, was effectively optimized as a superior electrode and yielded the greatest pseudocapacitance. This study indicates that forming a 3D nanonetwork is a straightforward means of improving the electrochemical properties of a supercapacitor.

  • 45. Edge-Exfoliated Graphites for Facile Kinetics of Delithiation ACS nano 6, 10770-10775 (2012)

    Jeong-Seok Park, Myeong-Hee Lee, In-Yup Jeon, Han-Saem Park, Jong-Beom Baek,* Hyun-Kon Song*

    As high rate charge and discharge characteristics of energy storage devices become more important with the market of electric vehicles intensively growing, the kinetics of lithiation or delithiation of electrode materials for lithium ion batteries are required to be enhanced. Graphites, the most widely used anode materials, have a limited power density at high discharge rates while their alternatives such as silicon and transition metal oxides show even inferior rate capability. This work was motivated from an idea of what if the edge opening of graphite was zipped more open to lithium ions in electrolyte. By edge-selective functionalization, the peripheral d-spacing of graphite (d0) was locally controlled. Larger values of d0 led to higher capacity especially at high discharge rates. Around two-fold enhancement of capacity or energy density was achieved at 50C discharge rate from 110 mAh/g to 190 mAh/g by exfoliating graphite locally in its edge region. Also, the d0 dependency of delithiation kinetics confirmed that the electrochemical step of Li+ influx into or efflux out of interlayer space of graphite is possibly the rate determining step of lithiation or delithiation.

  • 44. Hybrid multilayer thin film supercapacitor of graphene nanosheets with polyaniline: importance of establishing intimate electronic contact through nanoscale blending J. Mater. Chem. 22, 21092-21099 (2012)

    Taemin Lee , Taeyeong Yun , Byeongho Park , Bhawana Sharma , Hyun-Kon Song and Byeong-Su Kim*

    A hybrid electrode consisting of an electric double-layer capacitor of graphene nanosheets and a pseudocapacitor of the conducting polymer polyaniline exhibits a synergistic effect with excellent electrochemical performance for flexible thin film supercapacitors. This hybrid supercapacitor is constructed by a nanoscale blending method of layer-by-layer (LbL) assembly based on the electrostatic interactions between positively charged polyaniline (PANi) and negatively charged graphene oxide (GO) nanosheets. The hybrid electrode provides not only improved electronic conductivity through the intimate contact with the graphene nanosheet, but also enhanced chemical stability during the charge–discharge process. We also investigated the dependence of the electrochemical performance on the various parameters of LbL assembly such as the number of bilayers and the post-thermal and chemical treatments that could affect the degree of reduction of GO and PANi. We found that after thermal treatment, the LbL-assembled thin film of PANi with GO nanosheets exhibited an excellent gravimetric capacitance of 375.2 F g−1 at a discharge current density of 0.5 A g−1 that outperformed many other hybrid supercapacitors reported to date. The hybrid supercapacitor maintained its capacity up to 90.7% over 500 cycles at a high current density of 3.0 A g−1. This study opens up the possibility for the production of diverse graphene-based hybrid nanocomposites that are promising for future flexible supercapacitors.

  • 43. Catalytic carbonization of an uncarbonizable precursor by transition metals in olivine cathode materials of lithium ion batteries J. Mater. Chem. 22, 20305-20310 (2012)

    Han-Saem Park, Tae-Hee Kim, Myeong-Hee Lee and Hyun-Kon Song*

    Herein, we report on catalytic effects of transition metals (Me) in phospho-olivines (LiMePO4) on carbonization of cetyltrimethylammonium bromide (CTAB). Carbon coating is the required process to enhance electronic conductivity of phospho-olivines that are used as cathode materials for lithium ion batteries. Primary particles of phospho-olivines were in situ coated with CTAB and the adsorbed carbon precursor was carbonized to provide electrically conductive pathway. CTAB was successfully carbonized in a significant amount with Fe in phospho-olivines (LiFexMn1-xPO4 with x=1 and 0.5) even if CTAB is thermally decomposed around 300 °C without any residual mass in absence of the phospho-olivines. LiMnPO4 was the most inferior in terms of CTAB adsorption and thermal carbonization. LiNiPO4 and LiCoPO4 showed inefficient conversion of adsorbed CTAB to carbon even if their adsorption ability of CTAB is quite large. Also, the effect of the amount of carbon coating on LiFePO4 was investigated, leading to a conclusion that the carbon thickness balanced between electronic and ionic conductance results in the best electrochemical performances of lithium ion batteries specifically at high discharge rates.

  • 42. Carbon-Coated Single-Crystal LiMn2O4 Nanoparticle Clusters as Cathode Material for High-Energy and High-Power Lithium-Ion Batteries Angewandte Chemie International Edition 51, 8748-8752 (2012)

    Sanghan Lee, Yonghyun Cho, Hyun-Kon Song, Kyu Tae Lee, Jaephil Cho*

  • 41. Graphene Multilayer Supported Gold Nanoparticles for Efficient Electrocatalysts toward Methanol Oxidation Advanced Energy Materials, 2, 1510-1518 (2012)

    Yuri Choi, Minsu Gu, Jongnam Park, Hyun-Kon Song and Byeong-Su Kim*

  • 40. Versatile Double Hydrophilic Block copolymer: Dual Role as Synthetic Nanoreactor and Ionic and Electronic Conduction Layer for Ruthenium Oxide Nanoparticle Supercapacitor J. Mater. Chem., 22, 11598-11604 (2012)

    Eunyong Seo, Taemin Lee, Kyu Tae Lee, Hyun-Kon Song and Byeong-Su Kim*

  • 39. The Current Move of Lithium Ion Batteries towards the Next Phase Advanced Energy Materials, 2, 860–872 (2012)

    Tae-Hee Kim, Jeong-Seok Park, Sung Kyun Chang, Seungdon Choi,* Ji Heon Ryu,* Hyun-Kon Song*

    Application targets of lithium ion batteries (LIBs) are moving from small-sized mobile devices of information technology to large-scale electric vehicles (xEVs) and energy storage systems (ESSs). Environmental issues and abruptly increasing power demands are pushing high performance energy storage devices or systems onto markets. LIBs are one of the most potential candidates as the energy storage devices mainly due to their high energy densities with fairly good rate capabilities and a fairly long cycle life. As battery systems become larger in terms of stored energy as well as physical size, the safety concerns should be more seriously cared. Each application target has its own specification so that electrode materials should be chosen to meet requirements of the corresponding application. This report diagnoses the current market trends of LIBs as a primary topic, followed by giving an overview of anode and cathode material candidates of LIBs for xEVs and ESSs based on their electrochemical properties.

  • 38. A polymer electrolyte-skinned active material strategy toward high-voltage lithium ion batteries: polyimide-coated LiNi0.5Mn1.5 spinel cathode material case Energy & Environmental Science, 5, 7124-7131 (2012)

    Ju-Hyun Cho, Jang-Hoon Park, Myeong-Hee Lee, Hyun-Kon Song,* Sang-Young Lee*

    Top 10 most read in April, May 2012

    A facile approach to the surface modification of spinel LiNi0.5Mn1.5O4 (LNMO) cathode active materials for high-voltage lithium ion batteries is demonstrated. This strategy is based on the nanoarchitectured polyimide (PI) gel polymer electrolyte (GPE) coating. The PI coating layer successfully wrapped a large area of the LNMO surface via thermal imidization of 4-component (pyromellitic dianhydride/biphenyl dianhydride/phenylenediamine/oxydianiline) polyamic acid. In comparison to conventional metal oxide-based coatings, distinctive features of the unusual PI wrapping layer are the highly-continuous surface coverage with nanometer thickness (~ 10 nm) and the provision of facile ion transport. The nanostructure-tuned PI wrapping layer served as an ion-conductive protection skin to suppress the undesired interfacial side reactions, effectively preventing the direct exposure of LNMO surface to liquid electrolyte. As a result, the PI wrapping layer played a crucial role in improving the high-voltage cell performance and alleviating the interfacial exothermic reaction between charged LNMO and liquid electrolyte. Notably, the superior cycle performance (at 55 oC) of PI-wrapped LNMO (PI-LNMO) was elucidated in great detail by quantitatively analyzing manganese (Mn) dissolution, cell impedance, and chemical composition (specifically, lithium fluoride (LiF)) of byproducts formed on the LNMO surface.

  • 37. Optimized evolution of a secondary structure of LiFePO4: Balancing between shape and impurity Journal of Materials Chemistry, 22, 8228-8234 (2012)

    Myeong-Hee Lee, Tae-Hee Kim, Young Soo Kim, Jeong-Seok Park and Hyun-Kon Song*

    Top 10 most read in May 2012

    Kinetically helpful hollow secondary structure of LiFePO4 olivine (LFP) was optimized by balancing between its impurity and shape. In a thermodynamic process using hydrothermal treatment (+HyT), relatively less amount of hollow structure was developed without any impurity by a sequential precipitation method using the difference of solubility products (Ksp) between two precipitates (Li3PO4 and Fe3(PO4)2). On the other hand, a kinetically controlled process without hydrothermal treatment (-HyT) produced the contrary results of more amount of hollow structure with an impurity (Li3PO4). By removing the impurity of LFP from the latter process (-HyT*), therefore, optimized hollow LFP was obtained without impurities. The resultant cathode material showed enhanced capacities especially at high rate discharges due to its improved accessibility of ions into primary particles of the hollow secondary structure of LFP.

  • 36. Restricted Growth of LiMnPO4 Nanoparticles Evolved from a Precursor Seed Journal of Power Sources, 210, 1-6 (2012)

    Tae-Hee Kim, Han-Saem Park, Myeong-Hee Lee, Sang-Young Lee* and Hyun-Kon Song*

    Herein, we report on a novel precipitation method to enable LiMnPO4 olivine (LMP) as a cathode material for lithium ion batteries (LIBs) to reach high capacity at high discharge rates. By confining Mn3(PO4)2 precipitation on surface of a precursor seed of Li3PO4, the size of LMP particles are limited to less than 100 nm for a smaller dimension. The cathode material delivers discharge capacities of 145 mAh g-1 at 0.1C, 112 mAh g-1 at 1C to 62 mAh g-1 at 5C (comparable with top three performances[1-3] in Fig. S1 of Supporting Information). Even if precipitation were one of the versatile strategies to prepare the cathode material, it has not been reported that such a first-tier high performance is obtained from LMP prepared by precipitation methods. When compared with LMP particles synthesized by a conventional co-precipitation method, the performances are recognized to be considerably enhanced. Also, the surface-confined precipitation process described in this work does not involve a ball milling step with a conductive agent such as carbon black[1,2,4-10] so that a low cost synthesis is feasible.

  • 35. Scalable approach to multi-dimensional bulk Si anodes via metal-assisted chemical etching Energy & Environmental Science, 4, 5013-5019 (2012)

    Byoung Man Bang, Hyunjung Kim, Hyun-Kon Song, Jaephil Cho and Soojin Park*

    Specific design and optimization of the configuration of micro-scale materials can effectively enhance battery performance, including volumetric density. Herein, we employed commercially available low-cost bulk silicon powder to produce multi-dimensional silicon composed of porous nanowires and micro-sized cores, which can be used as anode materials in lithium-ion batteries, by combining a metal deposition and metal-assisted chemical etching process. Nanoporous silicon nanowires of 5–8 μm in length and with a pore size of 10 nm are formed in the bulk silicon particle. The silicon electrodes having multi-dimensional structures accommodate large volume changes of silicon during lithium insertion and extraction. These materials show a high reversible charge capacity of 2400 mAh g−1 with an initial coulombic efficiency of 91% and stable cycle performance. The synthetic route described herein is simple, low-cost, and mass producible (high yield of 40–50% in tens of gram scale), and thus, provides an effective method for producing high-performance anode materials.

  • 34. Fourier Transform Electrochemical Impedance Spectroscopic Studies on LiFePO4 Nanoparticles of Hollow Sphere Secondary Structures Journal of The Electrochemical Society, 158, A1267-A1274 (2011)

    Geun Gi Min, Younghoon Ko, Tae-Hee Kim, Hyun-Kon Song, Seung Bin Kim, and Su-Moon Park*

    Real-time impedance behaviors of LiFePO4 nanoparticles of two different structures have been investigated as cathode materials for lithium ion batteries using real time Fourier transform electrochemical impedance spectroscopy (FTEIS) techniques during potentiodynamic charging and discharging cycles. The effects of their nanostructures were examined employing hollow sphere secondary structured LiFePO4 particles prepared by sequential precipitations and commercially available non-hollow structured LiFePO4 particles. The battery constructed with the hollow sphere secondary structured LiFePO4 cathode material exhibited improved performances during charging and discharging processes as judged from various impedance parameters compared to those observed for the cell using its non-hollow counterpart. These results appear to have resulted from the enhancement of intrinsic capabilities for electron and charge transport characteristics of LiFePO4 by modifying its secondary structures. The real time impedance measurements were shown to be powerful in studying behaviors of battery electrodes during charging and discharging processes.

  • 33. One-dimensional (1D) nanostructured and nanocomposited LiFePO4: its perspective advantages for cathode materials of lithium ion batteries Physical Chemistry Chemical Physics, 13, 19226-19237 (2011)

    Viswanathan S. Saji, Young-Soo Kim, Tae-Hee Kim, Jaephil Cho and Hyun-Kon Song*

    Nanostructured materials have attracted recent research interests as battery materials due to their expected enhancement of properties. Characteristic nanoscale dimension and its structuring guarantees improved charge and mass transfer during charge/discharge processes. Among the potential cathode materials investigated as a substitute to LiCoO2, one of the most promising materials is LiFePO4 with olivine structure (LFP). In this perspective article, the current research and development in the synthesis and electrochemical studies of nanostructured LFP are reviewed with a special emphasis on one-dimensional (1D) nanostructures and nanocompositing with 1D conductive materials. In addition to various examples of 1D LFP with detailed synthetic methods, why 1D nanostructure could be meaningful is discussed in terms of a geometric point of view and the anisotropic lithiation/de-lithiation mechanism of LFP.

  • 32. Organic-skinned Inorganic Nanoparticles: Surface-confined Polymerization of 6-(3-Thienyl)hexanoic Acid Bound to Nanocrystalline TiO2 Nanoscale research letters, 6, 521 (2011)

    Viswanathan S. Saji, Yimhyun Jo, Hoi Ri Moon,* Yongseok Jun,* Hyun-Kon Song*

    There are many practical difficulties in direct adsorption of polymers onto nanocrystalline inorganic oxide surface such as Al2O3 and TiO2 mainly due to the insolubility of polymers in solvents or polymer agglomeration during adsorption process. As an alternative approach to the direct polymer adsorption, we propose surface-bound polymerization of pre-adsorbed monomers. 6-(3-thienyl)hexanoic acid (THA) was used as a monomer for poly[3-(5-carboxypentyl)thiophene-2,5-diyl] (PTHA). PTHA-coated nanocrystalline TiO2/FTO glass electrodes were prepared by immersing THA-adsorbed electrodes in FeCl3 oxidant solution. Characterization by ultraviolet/visible/infrared spectroscopy and thermal analysis showed that the monolayer of regiorandom-structured PTHA was successfully formed from intermolecular bonding between neighbored THA surface-bound to TiO2. The anchoring functional groups (-COOH) of the surface-crawling PTHA were completely utilized for strong bonding to the surface of TiO2.

  • 31. Ionic Liquid Modified Graphene Nanosheet Anchoring Manganese Oxide Nanoparticles as Efficient Electrocatalysts for Zn-Air Battery Energy & Environ. Sci., 4, 4148-4154 (2011)

    Jang-Soo Lee, Taemin Lee, Hyun-Kon Song, Jaephil Cho,* and Byeong-Su Kim*

    Ionic liquid (IL) modified reduced graphene oxide (rGO-IL) nanosheet anchoring manganese oxide (Mn3O4) are synthesized via a facile solution-based growth mechanism and applied to Zn-air battery as effective electrocatalysts for oxygen reduction reaction (ORR). In this study, IL moiety in these composites increases not only conductivity of the system, but also electrocatalytic activity compared to pristine rGO, together with the synergic effect of facilitating ORR with the intrinsic catalytic activity of Mn3O4. Based on the Koutecky-Levich plot, we suggest that the ORR pathway of these composites is tunable with the relative amount of Mn3O4 nanoparticles supported onto the graphene sheets; for example, ORR mechanism of the system with lower contents of Mn3O4 (19.2%) nanoparticles is similar to a Pt/C electrode, one-step, quasi-4-electron transfer, unlike that with higher contents of Mn3O4 (52.5%) which undergo a classical two-step, 2-electron pathway. We also demonstrate the potential of these hybrid rGO-IL/Mn3O4 nanoparticles as efficient catalysts for ORR in the Zn-air battery with a maximum peak power density of 120 mW/cm2; a higher performance than that from commercial cathode catalysts.

  • 30. Electronegativity-induced enhancement of thermal stability by succinonitrile as an additive for Li ion batteries Energy & Environ. Sci., 4, 4038-4045 (2011)

    Young-Soo Kim, Tae-Hee Kim, Hochun Lee, Hyun-Kon Song*

    Succinonitrile (SN, CN-[CH2]2-CN) is evaluated as an additive improving thermal stability in ethylene carbonate (EC)-based electrolyte for lithium ion batteries. Without any sacrifice of performances such as cyclability and capacity, introduction of SN into electrolyte with graphite anode and LixCoO2 cathode leads to (1) reducing the amount of gas emitted at high temperature, (2) increasing onset temperature of exothermic reactions and (3) decreasing the amount of exothermal heat. The improvement of thermal stability is considered to be due to a strong complex formation between surface metal atoms of LixCoO2 and nitrile (-CN) groups of SN, by spectroscopic studies based on photoelectrons induced by X-rays and by considering that the exothermic heat and gas evolution are caused by interfacial reactions between electrolyte and cathode.

  • 29. Precipitation revisited: shape control of LiFePO4 nanoparticles by combinatorial precipitation J. Phys. Chem. C, 115, 12255–12259 (2011)

    Myeong-Hee Lee, Tae-Hee Kim, Young Soo Kim and Hyun-Kon Song*

    Tunable precipitation strategy to control the shape of nanoparticles of a three-component system is presented. The strategy is devised from understanding the effects of precursor addition sequences on morphology of resultant precipitates. LiFePO4, one of the most potential candidate as a cathode material of lithium ion batteries for electric vehicles, was used as a representative model of the three (Li, Fe and PO4)-component system. According to the precursor addition sequence, three different precipitation methods were adopted: co-precipitation (Copr) and two different types of sequential precipitations (Seq1 and Seq2). Solubility product (Ksp) of intermediate precipitates (Li3PO4 and Fe3(PO4)2) is the key parameter to help the precipitation processes understood. In Copr, the intermediate precipitates are formed simultaneously under Ksp-governed competition. In Seq1 and Seq2, Li3PO4 precipitates prior to Fe3(PO4)2. When Fe2+ is introduced into the suspension of Li3PO4, the pre-formed precipitate is sacrificed to supply PO43- for Fe3(PO4)2 precipitation due to the stronger tendency (smaller value of Ksp) of precipitation of Fe3(PO4)2. Also, the interaction between a cationic surfactant and PO43- makes the difference between Seq1 and Seq2. As a conclusion of the effects of precursor sequence, the shape of particles spans from spherical nanoparticles through a hollow sphere secondary structure of the same nanoparticles to nano-plates. Each own morphology developed by different precipitation methods leads to different intercalation/de-intercalation behavior of lithium ions in conventional rechargeable battery cells.

  • 28. Suppression of the loss of an electroactive dopant from polypyrrole by using a non-aqueous electrolyte of dopant-phobicity Journal of Electroanalytical Chemistry 657, 181-186 (2011)

    Ryeo Yun Hwang, Sung Yeol Kim, G. Tayhas R. Palmore, Hyun-Kon Song*

    Loss of electroactive dopants from conducting polymers (CPs) was investigated by electrochemical quartz crystal microgravimetry (EQCM). pPy[ABTS], polypyrrole doped with ABTS (2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonate), was used as a model system. Two different kinds of electrolytes were used for studying the loss of dopants under electrochemical stimuli: one is a solvent to dissolve the dopant (dopant-philic) while the dopant is insoluble in the other (dopant-phobic). Degradation of polypyrrole backbone as well as loss of the dopant from pPy[ABTS] was observed in the dopant-philic electrolyte. Severe chemical overoxidation of polypyrrole by the most oxidized state of ABTS {(ABTS2+)2-} was emphasized as a factor responsible for de-doping in addition to potential-driven overoxidation or ion exchange. In the dopant-phobic electrolyte, however, the chemical degradation of the polymer film was suppressed.

  • 27. Who will drive electric vehicles, olivine or spinel? Energy & Environmental Science, 4, 1621-1633 (2011)

    Ok Kyung Park, Yonghyun Cho, Sanghan Lee, Ho-Chun Yoo, Hyun-Kon Song,* Jaephil Cho*

    Lithium iron phosphate olivine (LFP) and lithium manganese oxide spinel (LMO) is competitive and complementary to each other as cathode materials for lithium ion batteries especially for hybrid electric vehicles and electric vehicles. The interests in the materials due to their low cost and high safety have pushed research and development forward and toward high performance in terms of rate capability and capcity retention or cyclability at high temperature of around 60 oC. From the view point of basic properties, LFP shows a higher gravimetric capacity while LMO has better conductivities electrically and ionically. Accoding to our comparison experiments, depending on the material properties and operational potential window, LFP was favored for fast charging while LMO led to better discharge performances. Capacity fading at high termparue due to metal dissolution was revealed to be the most problematic issue of LFP and LMO-based cells for EVs (with thicker electrodes) in the case of no additive in electrolyte and no coating to prevent metal dissolution on cathode materials. Various strategies to enhance properties of LFP and LMO are ready for reallizing EVs in the near future.

  • 26. The effect of introducing a buffer layer to polymer solar cells on cell efficiency Solar Energy Materials & Solar Cells, 95, 1119-1122 (2011)

    Gi-Hwan Kim, Hyun-Kon Song*, Jin Young Kim*

    The effect of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) as a buffer layer was investigated in polymer solar cells (PSCs). Four different types of PEDOT:PSS were used: PH, PH500 and their DMSO (dimethylsulfoxide)-doped counterparts. The efficiency of PSCs was independent of the electric conductivity of the buffer layer as a bulk property while it was significantly related to interfacial properties between the buffer layer and a bulk-heterojunction (BHJ) layer. The interfacial properties included charge transfer resistance, hole mobility and contact angle of the solution of BHJ on the buffer layer. Lower charge transfer resistance, higher hole mobility and smaller contact angle led to the higher fill factor (up to 72%), enabling highly efficient PSCs with efficiency = 4.25%.

  • 25. Quantitative control of neuron adhesion at a neural interface using a conducting polymer composite with low electrical impedance ACS Applied Materials & Interfaces, 3, 16-21 (2011)

    Sung Yeol Kim, Kwang-Min Kim, Diane Hoffman-Kim, Hyun-Kon Song, G. Tayhas R. Palmore*

    Tailoring cell response on an electrode surface is essential in the application of neural interfaces. In this paper, a method of controlling neuron adhesion on the surface of an electrode was demonstrated using a conducting polymer composite as an electrode coating. The electrodeposited coating was functionalized further with biomolecules-of-interest (BOI), their surface concentration controlled via repetition of carbodiimide chemistry. The result was an electrode surface that promoted localized adhesion of primary neurons, the density of which could be controlled quantitatively via changes in the number of layers of BOI added. Important to neural interfaces, it was found that additional layers of BOI caused an insignificant increase in electrical impedance, especially when compared to the large drop in impedance upon coating the electrode with the conducting polymer composite.

  • 24. Ladder-type heteroacene polymers bearing carbazole and thiophene ring units and their use in field-effect transistors and photovoltaic cells J. Mater. Chem., 21, 843-850 (2011)

    Ravi Kumar Cheedarala, Gi-Hwan Kim, Shinuk Cho, Junghoon Lee, Jonggi Kim, Hyun-Kon Song, Jin Young Kim and Changduk Yang*

    A family of ladder-type ?ð-excessive conjugated monomer (dicyclopentathienocarbazole (DCPTCz)) integrating the structural components of carbazole and thiophene into a single molecular entity is synthesized and polymerized by oxidative coupling to yield poly(dicyclopentathienocarbazole) (PDCPTCz). Moreover, through the careful selection of 2,1,3-benzothiadiazole unit as a ?ð-deficient building block, the dicyclopentathienocarbazole-based donor–acceptor copolymer (poly(dicyclopentathienocarbazole-alt-2,1,3-benzothiadiazole) (PDCPTCz-BT)) is prepared by Suzuki polycondensation. The optical, electrochemical, and field-effect charge transport properties of the resulting polymers (PDCPTCz and PDCPTCz-BT) are not only characterized in detail but also their bulk-heterojunction (BHJ) solar cell in combination with PC71BM are evaluated. The values of field-effect mobility (µ) for PDCPTCz and PDCPTCz-BT are 8.7 ¡¿ 10−6 cm2 V−1 s−1 and 2.7 ¡¿ 10−4 cm2 V−1 s−1, respectively. A power conversion efficiency (PCE) of 1.57% is achieved on the PDCPTCz-BT/PC71BM device, implying that the push–pull copolymers based on ladder-type dicyclopentathienocarbazole as an electron-donating moiety are promising for organic electronic devices.

  • 23. A Hollow Sphere Secondary Structure of LiFePO4 Nanoparticles Chemical Communications, 46, 6795-6797 (2010)

    Myeong-Hee Lee, Jin-Young Kim, Hyun-Kon Song*

    We report on the evolution of a hollow sphere secondary structure of spherical nanoparticles by a solubilization-reprecipitation mechanism based on the difference of solubility products (Ksp) of two different precipitates. Carbon-coated nanoparticles of olivine structure LiFePO4 served as the primary nano-blocks to build the secondary nano-architecture.

  • 22. Recent Progress in Nanostructured Cathode Materials for Lithium Secondary Batteries Advanced Functional Materials, 20, 3818-3834 (2010) Feature Article

    Hyun-Kon Song, Kyu Tae Lee, Min Gyu Kim, Linda F. Nazar,* Jaephil Cho*

    Diversified and extended applications of lithium ion batteries demand the development of more enhanced materials that can be achieved by sophisticated synthetic methods. Combination of novel materials with strategic design of their shape in a nanometer scale enables a breakthrough to overcome problems that present technologies have. In this feature article, Mn-based and polyanion-based cathodic cathode materials with nano-scale features for lithium ion batteries are overviewed as the materials coming after conventional bulk cathodic cathode materials. Various synthetic methods coupled with nanostructuring as well as the benefits obtained from the nanostructure are described.

  • 21. Enhancing the stability and performance of a battery cathode using a non-aqueous electrolyte Electrochemistry Communications 12, 761–764 (2010)

    Sung Yeol Kim, Sujat Sen, Hyun-Kon Song, G. Tayhas R. Palmore*

    For conductive polymers to be considered materials for energy storage, both their electroactivity and stability must be optimized. In this study, a non-aqueous electrolyte (0.2 M LiClO4 in acetonitrile) was studied for its effect on the charge storage capacity and stability of two materials used in batteries developed in our laboratory, polypyrrole (pPy) and poly(3,4-ethylenedioxythiophene) (PEDOT) doped with 2,2¡?-azinobis(3-ethylbenzothiaxoline-6-sulfonic acid (ABTS). The results are compared to the performance of these materials in an aqueous electrolyte (0.2 M HCl/aq). Loss of ABTS dopant was eliminated principally due to the low solubility of ABTS in acetonitrile, resulting in cathode materials with improved stability in terms of load cycling and performance.

  • 20. Direct Electron Transfer of Glucose Oxidase and Carbon Nanotubes Entrapped with Biocompatible Organic Materials
    Mol. Cryst. Liq. Cryst. 519, 82–89 (2010)


    Efficient electron transfer between redox enzymes and electrodes is essential for enzyme-based biosensors, biofuel cells, and bioelectronic devices. Generally glucose oxidase (GOx) requires mediators for electrical communication with electrodes because the redox center of GOx is deeply buried in the insulating protein shell. In the present work, direct electron transfer (DET) between GOx and electrodes was attempted. GOx and carbon nanotubes (CNTs) were immobilized on a glassy carbon (GC) electrode by using biocompatible polymer, chitosan (CHI). Cyclic voltammograms revealed that the CHI=GOx=CNT-GC electrode showed a pair of well-defined redox peaks in 0.1Mphosphate buffer solution (pH 7.0) saturated with argon. Under the same conditions, no redox peak was observed in the absence of CNTs. The formal redox potential was 450mV (vs. Ag=AgCl), which agreed well with that of FAD=FADH2, the redox center of GOx. This result clearly shows that the DET between the GOx and the electrode was achieved. The use of thin CNTs significantly improved the DET efficiency of the GOx. It was found that the GOx immobilized on the electrode retained catalytic activity for the oxidation of glucose.

  • 19. Colloidal Nanoparticles as a Wireless Booster for Electroenzymatic Reactions
    Small 5, 2162-2166 (2009)

    Sahng Ha Lee, Keehoon Won, Hyun-Kon Song*, Chan Beum Park*

    Nanoparticles in a wireless form are employed to overcome the extremely low efficiency of electroenzymatic synthesis reactions. The nanoparticle-mediated electrochemical regeneration of cofactor (NADH) is used in the enzymatic conversion of -ketoglutarate to L-glutamate (see picture). The use of colloidal nanoparticles in electrolyte provides a new strategy for electroenzymatic catalysis.

  • 18. Electrochemical Regeneration of NADH Enhanced by Platinum Nanoparticles
    Angew. Chem. Int. Edn. 47, 1749-1752 (2008)

    Hyun-Kon Song, S. H. Lee, K. Won, J. H. Park, J. K. Kim, H. Lee, S. –J. Moon, D. K. Kim, C. B. Park*

    Nanotechnology-inside wireless chemical communication: Platinum nanoparticles (nPt) in electrolyte enhance electron transfer from electrode to NAD+ in electrolyte during an indirect electrochemical regeneration of NADH. The intermediate nPt-Hads, formed at negative potential, helps the primary mediator M¡?s turnover by donating proton and electron in a kinetically favorable way.

  • 17. A biopolymer composite that catalyzes the reduction of oxygen to water
    Chem. Mater. 19, 1565-1570 (2007)

    Jiangfeng Fei, Hyun-Kon Song, and G. Tayhas R. Palmore*

    A biopolymer composite consisting of polypyrrole, ABTS, and laccase (PAL) was electrodeposited onto the surface of an electrode and shown to catalyze the reduction of dioxygen to water under acidic conditions. The catalytic activity of this biopolymer composite is highest at pH 4, decreasing with increasing pH. The activity of laccase immobilized within this polymer composite was found to be higher than laccase dissolved in solution when methanol was present or at elevated temperatures.

  • 16. Redox-active Polypyrrole: Toward polymer-based batteries
    Adv. Mater. 18, 1764-1768 (2006)

    Hyun-Kon Song and G. Tayhas R. Palmore

    Highlighted in Research News at Materials Today 9, p10 (2006)

    The redox-active conducting polymer battery (pPy[IC] pPy[ABTS]), consisting of two conducting polymer electrodes incorporated with different electroactive dopants, was developed. Polypyrrole (pPy) was used as the conducting polymer with indigo carmine (IC) and 2,2'-azinobis (3-ethylbenzothiazoline-6-sulfonate) (ABTS) as dopants. The pPy[IC] pPy[ABTS] showed dramatically enhanced performance at high power density (energy density = 8 Wh kg-1 at power density = 10^2 to 10^4 W kg-1).

  • 15. Combined topographical and chemical micropatterns for templating neuronal networks
    Biomaterials 27, 5734-5739 (2006)

    J. Zhang, S. Venkataramani, H. Xu, Y-K Song, Hyun-Kon Song, G.T.R. Palmore, J. Fallon and A.V. Nurmikko

    In-vitro neuronal networks with geometrically defined features are desirable for studying long-term electrical activity within the neuron assembly and for interfacing with external microelectronic circuits. In standard cultures, the random spatial distribution and overlap of neurites makes this aim difficult; hence many recent efforts have been made on creating patterned cellular circuits. Here, we present a novel method for creating a planar neural network that is compatible with optical devices. This method combines both topographical and chemical micropatterns onto which neurons can be cultured. Compared to other reported patterning techniques, our approach and choice of template appears to show both geometrical control over the formation of specific neurite connections at low plating density and compatibility with microelectronic circuits that stimulate and record neural activity.

  • 14. Micropatterns of positive guidance cues anchored to polypyrrole doped with polyglutamic acid: A new platform for characterizing neurite extension in complex environments
    Biomaterials 27, 473-484 (2006)

    Hyun-Kon Song, Beth Toste, Katherine Ahmann, Diane Hoffman-Kim, and G. Tayhas R. Palmore

    This paper describes a method for preparing substrates with micropatterns of positive guidance cues for the purpose of stimulating the growth of neurons. This method uses an oxidizing potential, applied to a micropattern of indium tin oxide in the presence of pyrrole and polyglutamic acid, to electrodeposit a matrix consisting of polypyrrole doped with polyglutamic acid. The resulting matrix subsequently can be modified with positive guidance cues via standard amide coupling reactions. Cells adhered to the micropatterned substrates can be stimulated electrically by the underlying electrodeposited matrix while they are in contact with positive guidance cues. This method can be extended to include both positive and negative guidance cues in a variety of combinations. To demonstrate the suitability of this method in the context of nerve guidance, dorsal root ganglia were grown in the presence of a micropatterned substrate whose surface was modified with molecules such as polylysine, laminin, or both. Cell adhesion and neurite extension were found to occur almost exclusively in areas where positive guidance cues were attached. This method is easy to execute and is of general utility for fundamental studies on the behavior of neurons in the presence of complex combinations of guidance cues as well as advanced bio-electronic devices such as neuronal networks.

  • 13. Electrochromism of 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) Incorporated into Conducting Polymer as a Dopant
    Chem. Mater., 17, 2232-2233 (2005)

    Hyun-Kon Song, Eun Ju Lee and Seung M. Oh

    Polypyrrole films doped with ABTS {2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate)} show multi-color electrochromism: the anodic coloration from brown at 0.0 V to greenish blue at 0.8 V due to oxidation of ABTS to its radical; and the cathodic coloration to yellow (-1.0 V) based on the reduction of polypyrrole itself.

  • 12. Conductive Polypyrrole via Enzyme Catalysis
    J. Phys. Chem. B., 109, 19278-19287 (2005)

    Hyun-Kon Song and G. Tayhas R. Palmore

    Laccase catalyzes the polymerization of pyrrole into a conducting polymer using dioxygen as the terminal oxidant. This finding is significant because it identifies an enzymatic route, and thus an environmentally benign method, for preparing a technologically important polymer. In addition, the rate of oxidation of pyrrole increases when the redox molecule, ABTS {2,2'-azinobis (3-ethylbenzothiazoline-6-sulfonate)}, is included in a reaction medium that contains laccase. This increase in rate occurs because laccase catalyzes the oxidation of ABTS to ABTS•. In addition to laccase, the biocatalytically-generated ABTS• oxidizes pyrrole to its corresponding radical cation to yield polypyrrole. Moreover, oxidation of pyrrole by ABTS• regenerates ABTS for subsequent biocatalytic turnover. Including ABTS in the reaction medium has two important consequences on the final product: (a) the reaction proceeds fast enough to form polymeric films instead of oligomeric precipitates; and (b) ABTS remains within the polymeric film as a redox-active dopant. The charge transport properties of the resulting polymers, both with and without ABTS as the counter anion, are compared to those of other conducting materials including polypyrrole prepared electrochemically or chemically.

  • 11. Electrochemical Porosimetry: Deconvolution of Distribution Functions Electrochemistry Communication, 8, 1191-1196 (2006)

    Hyun-Kon Song, Jong H. Jang, Jae Jeong Kim, Seung M. Oh

    Discrete Fourier transform (DFT) was used to deconvolute distribution functions involved in Fredholm integral equation of the first kind. Fourier-transformed distribution function Nk was obtained by convolution theorem. The noise was removed by low-pass filtering the power spectral density Nk in Fourier space. Then, the distribution function nn was obtained from the noise-free Nk by inverse DFT. Several examples were tested: adsorption isotherm, and impedances for faradaic/resistive and non-faradaic/capacitive systems. The ¡°continuous periodicity¡± was the required property of the functions in the original space (the observed function p(x) and the kernel q(x)) for successful deconvolution. For continuous distributions, noise reduction was possible by low-pass filtering without a loss of information. On the other hand, for discontinuous distributions, the noise reduction process led to damping of the distributions.
  • 10. Electrochemical Porosimetry
    Journal of the Electrochemical Society, 151, E102-E109 (2004)
    Selected in Tech Highlights at Interface 13, p16 (2004)
    Hyun-Kon Song, Joo-Hwan Sung, Yong-Ho Jung, Kun-Hong Lee, Le H. Dao, Myung-Hwan Kim and Hyuk-Nyun Kim

    We have developed the electrochemical porosimetry (ECP) analyzing microstructures of porous electrodes in situ, which can give geometric information most meaningful in electrochemical systems. The methodology is based on a model that relates electrochemical impedance data with microstructural information. Pore length (lp), as well as pore size distribution (PSD), could be obtained by fitting the model to the experimental impedance data of a porous electrode. This geometric information was validated for the microporous, mesoporous and macroporous samples. Also, the ECP could be used as a nondestructive probe to investigate the construction of electrochemical devices.

  • 9. Electrochemical Porosimetry
    Electrically Based Microstructural Characterization III (Editors: R.A. Gerhardt, A. Washabaugh, M.A. Alim, G.M. Choi)- MRS Proceedings Volume 699, R7.7. (2002).

    Hyun-Kon Song, Kun-Hong Lee
  • 8. The Effect of Pore Size Distribution on the Frequency Dispersion of Porous Electrodes
    Electrochim. Acta, 45, 2241-2257 (2000)

    Hyun-Kon Song, Hee-Young Hwang, Kun-Hong Lee and Le. H. Dao
  • 7. The Effect of Pore Size Distribution on the Electrochemical Impedance of Porous Electrodes
    Electrochim. Acta, 44, 3513-3519 (1999)

    Hyun-Kon Song, Yong-Ho Jung, Kun-Hong Lee and Le. H. Dao
  • 6. Enhancement of Heat and Mass Transfer in Silica-Expanded Graphite Composite Blocks for Adsorption Heat Pumps-Part I. Characterization of the composite blocks Int. J. Refrigeration, 23, 64-73 (2000)

    T.-H. Eun, H.-K. Song, J. H. Han, K.-H. Lee and J.-N. Kim
    Composite blocks for adsorption heat pumps of water/silica gel systems were manufactured by mixing expanded graphite powders and silica gel powders, then by consolidating them via compressive molding. Optimum expansion condition was determined as 600°C for 10 min by investigating carbon and sulfur contents during expansion. Amounts of water adsorption, gas permeability and thermal conductivity were measured for the composite blocks prepared with various compositions and molding pressures. Expanded graphite in the composite blocks had no effects on the equilibrium adsorption amount of water on silica gel and increased the rate of adsorption. The composite blocks of 20–30% graphite fraction under 4–40 MPa molding pressure showed good permeability of 3 to 40×10−12 m2. Permeability increased with graphite fraction at constant molding pressure. Thermal conductivity of the composite blocks was 10–20 Wm−1 K−1 depending on the graphite bulk density (ρgr) in the block. It is a much higher value than 0.17 Wm−1 K−1 in silica-gel packed bed.
  • 5. Enhancement of Heat and Mass Transfer in Silica-Expanded Graphite Composite Blocks for Adsorption Heat Pumps-Part II. Cooling system using the composite blocks Int. J. Refrigeration, 23, 74-81 (2000)

    T.-H. Eun, H.-K. Song, J. H. Han, K.-H. Lee and J.-N. Kim
    Cooling systems using graphite/silica-gel composite blocks were built and their performances were compared with that of the silica gel packed bed. Spatial and temporal profiles of temperature in the composite blocks were obtained in axial and radial directions. The amount of adsorption and specific cooling powers for each composite block were also measured. It was shown that the axial profile of temperature was affected mainly by mass transfer while the radial distribution of temperature was largely due to poor heat transfer. When compared with a pure silica gel packed bed, both heat transfer and mass transfer were enhanced by using the composite blocks. As a result, the good mass and heat transfer of the composite blocks led to enhancement of performances of the cooling systems.
  • 4. Adsorption of carbon dioixde on the chemically modified adsorbents
    Int. J. Environ. Conscious Des. Manuf., 7, 53-56 (1998)

    Hyun-Kon Song and Kun-Hong Lee
  • 3. Adsorption of Carbon Dioxide on the Chemically Modified Silica Adsorbents
    J. Noncrystalline Solids, 242, 69-80 (1998)

    Hyun-Kon Song, Kil Won Cho and Kun-Hong Lee
  • 2. Adsorption of Carbon Dioxide on Chemically modified Carbon Adsorbents
    Sep. Sci. and Tech., 33, 2039-2057 (1998)

    Hyun-Kon Song and Kun-Hong Lee
  • 1. Manufacture of Biodegradable packaging Foams from Agar by Freeze-Drying Journal of Materials Science 32, 5825–5832 (1997)

    Jong-Pil Lee, Kun-Hong Lee and Hyun-Kon Song
    Cellular foams were made from the aqueous solution of agar by freeze-drying. A narrow range (5–20°C min-1) of freezing rate was required to avoid damage to the microstructure of the agar foams. The size of cells in the foam decreased with increasing freezing rate. Agar foams of more than 4 wt% agar content absorbed more energy than a polystyrene foam in compression tests. Foams with a higher agar content absorbed more energy. The behaviour of agar foams in compression tests could be explained by the modified beam theory for cellular foams. Agar foams were thermally stable up to 200°C, and were also stable in a humid environment.