Browsing by Author "Kang, B"
Now showing 1 - 5 of 5
Results Per Page
Sort Options
- ItemControlled atomic solubility in Mn‐rich composite material to achieve superior electrochemical performance for Li‐ion batteries(Wiley, 2019-12-16) Lee, J; Zhang, Q; Kim, J; Dupre, N; Avdeev, M; Jeong, M; Yoon, WS; Gu, L; Kang, BThe quest for high energy density and high power density electrode materials for lithium-ion batteries has been intensified to meet strongly growing demand for powering electric vehicles. Conventional layered oxides such as Co-rich LiCoO2 and Ni-rich Li(NixMnyCoz)O2 that rely on only transition metal redox reaction have been faced with growing constraints due to soaring price on cobalt. Therefore, Mn-rich electrode materials excluding cobalt would be desirable with respect to available resources and low cost. Here, the strategy of achieving both high energy density and high power density in Mn-rich electrode materials by controlling the solubility of atoms between phases in a composite is reported. The resulting Mn-rich material that is composed of defective spinel phase and partially cation-disordered layered phase can achieve the highest energy density, ≈1100 W h kg−1 with superior power capability up to 10C rate (3 A g−1) among other reported Mn-rich materials. This approach provides new opportunities to design Mn-rich electrode materials that can achieve high energy density and high power density for Li-ion batteries. © 1999-2021 John Wiley & Sons, Inc.
- ItemFully exploited oxygen redox reaction by the inter‐diffused cations in Co‐free Li‐rich materials for high performance Li‐ion batteries(Wiley, 2020-09-09) Lee, J; Dupre, N; Jeong, M; Kang, SY; Avdeev, M; Gong, Y; Gu, L; Yoon, WS; Kang, BTo meet the growing demand for global electrical energy storage, high-energy-density electrode materials are required for Li-ion batteries. To overcome the limit of the theoretical energy density in conventional electrode materials based solely on the transition metal redox reaction, the oxygen redox reaction in electrode materials has become an essential component because it can further increase the energy density by providing additional available electrons. However, the increase in the contribution of the oxygen redox reaction in a material is still limited due to the lack of understanding its controlled parameters. Here, it is first proposed that Li-transition metals (TMs) inter-diffusion between the phases in Li-rich materials can be a key parameter for controlling the oxygen redox reaction in Li-rich materials. The resulting Li-rich materials can achieve fully exploited oxygen redox reaction and thereby can deliver the highest reversible capacity leading to the highest energy density, ≈1100 Wh kg−1 among Co-free Li-rich materials. The strategy of controlling Li/transition metals (TMs) inter-diffusion between the phases in Li-rich materials will provide feasible way for further achieving high-energy-density electrode materials via enhancing the oxygen redox reaction for high-performance Li-ion batteries. © 2020 The Authors.
- ItemMultielectron-capable Li-rich polyanion material with high operating voltage: Li5V2PO4F8 for Li-ion batteries(American Chemical Society, 2019-12-13) Kim, MK; Avdeev, M; Kang, BPolyanion compounds have relatively low energy density compared to plain oxides as cathode materials. We for the first time report on a Li-rich fluorophosphate compound, Li5V2PO4F8, that can have high energy density originating from both the multielectron reaction of vanadium and high voltage induced by a fluorine. The developed material has a new crystal structure that has a robust three-dimensional framework of corner-sharing octahedra VO2F4 with tetrahedra PO4 and three-dimensional lithium ion diffusion pathways, which can facilitate the (de)intercalation of lithium ions. Its theoretical capacity is 285 mAh/g when two electrons are exploited. Practically, it shows the highest redox voltage, ∼4.4 V (vs Li/Li+), among V3+/V4+ redox reactions, with 111 mAh/g of reversible capacity. Only in the first charge does it show an active redox reaction of the V4+/V5+ at ∼4.9 V (vs Li/Li+) with 228 mAh/g of charge capacity. Moreover, the vanadium-deficient phase shows stable capacity retention and good rate capability at both charging and discharging rates up to the 2C rate. The discovery of the lithium- and fluorine-rich phosphate compounds reported here introduces a new family of cathode materials, and further exploration and optimization can be expected to unlock the full potential of this family. © 2019 American Chemical Society
- ItemNewly developed γ-NaTiOPO4 by simple solid-state synthesis for anode material of Na-ion batteries in both nonaqueous and aqueous electrolytes(Elsevier, 2022-09) Kim, D; Park, H; Avdeev, M; Kim, M; Kang, BSodium-ion batteries (SIBs) are a promising next-generation energy storage system in terms of cost due to the abundance of sodium. However, obtaining good anode materials for SIBs remains a challenge. NaTiOPO4 has been investigated as an anode not only for SIBs but also for aqueous SIBs. Despite the various NaTiOPO4 polymorphs, only the β-NaTiOPO4 phase has been investigated as an anode for SIBs due to the limited synthesis process. In this study, we successfully stabilized γ-NaTiOPO4 via our newly developed solid-state synthesis process. In addition, its electrochemical properties as an anode for SIBs were investigated in this study. The synthesized material demonstrates a high voltage of 1.7 and ∼1.5 V vs Na/Na+ with 120 mAh/g and good capacity retention of 64% for up to 500 cycles at 0.5C in a nonaqueous electrolyte. In an aqueous electrolyte, Na0·44MnO2//γ-NaTiOPO4 full cell achieves excellent stable capacity retention with a high Coulombic efficiency for 175 cycles. It shows high cycling stability with a three-dimensional framework despite the relatively high redox potential. Thus, it demonstrates that γ-NaTiOPO4 is a promising anode material for both nonaqueous and aqueous rechargeable SIBs. © 2022 Elsevier B.V. All rights reserved.
- ItemUnderstanding the cation ordering transition in high-voltage spinel LiNi0.5Mn1.5O4 by doping Li instead of Ni(Springer Nature, 2017-07-27) Lee, J; Dupre, N; Avdeev, M; Kang, BWe determined how Li doping affects the Ni/Mn ordering in high-voltage spinel LiNi0.5Mn1.5O4(LNMO) by using neutron diffraction, TEM image, electrochemical measurements, and NMR data. The doped Li occupies empty octahedral interstitials (16c site) before the ordering transition, and can move to normal octahedral sites (16d (4b) site) after the transition. This movement strongly affects the Ni/Mn ordering transition because Li at 16c sites blocks the ordering transition pathway and Li at 16d (4b) sites affects electrostatic interactions with transition metals. As a result, Li doping increases in the Ni/Mn disordering without the effect of Mn3+ ions even though the Li-doped LNMO undergoes order-disorder transition at 700 °C. Li doping can control the amount of Ni/Mn disordering in the spinel without the negative effect of Mn3+ ions on the electrochemical property. © 2021 Springer Nature Limited. Provided by the Springer Nature SharedIt content-sharing initiative.