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Kim, Jongsoon,Lee, Byungju,Kim, Hyungsub,Kim, Hyunah,Kang, Kisuk American Chemical Society 2016 Chemistry of materials Vol.28 No.19
<P>Defects in crystals such as antisites generally lead-to the deterioration of the ionic conductivity of solid-state ionic conductors. Herein, using first principles calculations, we demonstrate that the Li diffusion in Li2MP2O7 (M = Fe or Mn), a promising battery material, is sensitively affected by the presence of Li/M antisites; however, unexpectedly, the antisites significantly promote Li diffusion. The calculations reveal that the presence of antisites reduces the barrier of Li hopping and opens new paths for Li diffusion in the Li2MP2O7 crystal. In our experimental verification, we succeeded in synthesizing crystalline Li2MnP2O7 with varying Li/Mn antisite contents and demonstrated that the inclusion of antisites results in improved power capability with faster Li diffusion for Li-ion battery electrodes. We believe that this unexpected finding of increasing the ionic conductivity by introducing antisite defects broadens our understanding of solid-state ionic conductors and provides a new strategy for improving Li diffusion in conventional electrode materials for Li rechargeable batteries.</P>
Kim, Hyeri,Kim, Jongsoon,Jeong, Hee-Sung,Kim, Hyungsub,Lee, Hoyeon,Ha, Jae-Min,Choi, Sung-Min,Kim, Tae-Ho,Nah, Yoon-Chae,Shin, Tae Joo,Bang, Joona,Satija, Sushil K.,Koo, Jaseung The Royal Society of Chemistry 2018 Chemical communications Vol.54 No.41
<P>We demonstrate that hybrid structures of graphene and single-walled carbon nanotubes (SWNTs) are precisely controlled at the liquid-gas interface. The functionalized SWNT Langmuir monolayers anchor single-layer graphene nanosheets (GNSs) suspended in water <I>via</I> Coulomb interaction at the interface. This GNS/SWNT hybrid multilayer electrode can be a promising anode material for Li-ion batteries, offering high specific capacity, outstanding power capability, and excellent cyclability.</P>
Phase Stability Study of Li[sub 1−x]MnPO[sub 4] (0≤x≤1) Cathode for Li Rechargeable Battery
Kim, Sung-Wook,Kim, Jongsoon,Gwon, Hyeokjo,Kang, Kisuk The Electrochemical Society 2009 Journal of the Electrochemical Society Vol.156 No.8
<P>The phase stability of Li1-xMnPO4 (0 <= x <= 1) is investigated in this study for different Li compositions and temperatures by high temperature X-ray diffraction and electron microscopy. The map of stable phases is determined at temperature ranges between room temperature and 410 degrees C. While pure LiMnPO4 phase is stable at high temperature, partial phase transformation of MnPO4 into Mn2P2O7 is observed in delithiated phases above 210 degrees C. Electron microscopy study also indicates the instability of the delithiated phase. The morphology of LiMnPO4 is severely damaged upon delithiation. The instability of the delithiated phase and the phase transformation into Mn2P2O7 may imply that safety concerns can be raised regarding the LiMnPO4 cathode, unlike its Fe counterpart.</P>
Highly Stable Iron- and Manganese-Based Cathodes for Long-Lasting Sodium Rechargeable Batteries
Kim, Hyungsub,Yoon, Gabin,Park, Inchul,Hong, Jihyun,Park, Kyu-Young,Kim, Jongsoon,Lee, Kug-Seung,Sung, Nark-Eon,Lee, Seongsu,Kang, Kisuk American Chemical Society 2016 Chemistry of materials Vol.28 No.20
<P>The development of long-lasting and low-cost rechargeable batteries lies at the heart of the success of large-scale energy storage systems for various applications. Here, we introduce Fe- and Mn-based Na rechargeable battery cathodes that can stably cycle more than 3000 times. The new cathode is based on the solid-solution phases of Na4MnxFe3-x(PO4)(2)-(P2O7) (x = 1 or 2) that we successfully synthesized for the first time. Electrochemical analysis and ex situ structural investigation reveal that the electrodes operate via a one phase reaction upon charging and discharging with a remarkably low volume change of 2.1% for Na4MnFe2(PO4)(P2O7), which is one of the lowest values among Na battery cathodes reported thus far. With merits including an open framework structure and a small volume change, a stable cycle performance up to 3000 cycles can be achieved at 1C and room temperature, and almost 70% of the capacity at C/20 can be obtained at 20C. We believe that these materials are strong competitors for large-scale Na-ion battery cathodes based on their low costs, long-term cycle stability, and high energy density.</P>
New 4V-Class and Zero-Strain Cathode Material for Na-Ion Batteries
Kim, Jongsoon,Yoon, Gabin,Lee, Myeong Hwan,Kim, Hyungsub,Lee, Seongsu,Kang, Kisuk American Chemical Society 2017 Chemistry of materials Vol.29 No.18
<P>Here, we introduce Na<SUB>3</SUB>V(PO<SUB>3</SUB>)<SUB>3</SUB>N as a novel 4V-class and zero-strain cathode material for Na-ion batteries. Structural analysis based on a combination of neutron and X-ray diffraction (XRD) reveals that the Na<SUB>3</SUB>V(PO<SUB>3</SUB>)<SUB>3</SUB>N crystal contains three-dimensional channels that are suitable for facile Na diffusion. The Na (de)intercalation is observed to occur at ∼4 V vs Na/Na<SUP>+</SUP> in the Na cell via the V<SUP>3+</SUP>/V<SUP>4+</SUP> redox reaction with ∼67% retention of the initial capacity after over 3000 cycles. The remarkable cycle stability is attributed to the near-zero volume change (∼0.24%) and unique centrosymmetric distortion that occurs during a cycle despite the large ionic size of Na ions for (de)intercalation, as demonstrated by <I>ex situ</I> XRD analysis and first-principles calculations. We also demonstrate that the Na<SUB>3</SUB>V(PO<SUB>3</SUB>)<SUB>3</SUB>N electrode can display outstanding power capability with ∼84% of the theoretical capacity retained at 10C, even though the particle sizes are on the micrometer scale (>5 μm), which is attributed to its intrinsic three-dimensional open-crystal framework. The combination of this high power capability and extraordinary cycle stability makes Na<SUB>3</SUB>V(PO<SUB>3</SUB>)<SUB>3</SUB>N a new potential cathode material for Na-ion batteries.</P> [FIG OMISSION]</BR>