Browsing by Author "Hong, J"

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    Critical role of Ti4+ in stabilizing high-voltage redox reactions in Li-rich layered material
    (Wiley, 2021-07-01) Cho, M; Song, SH; Hong, S; Kim, KS; Avdeev, M; Yoo, JG; Ko, KT; Hong, J; Kim, J; Lee, S; Kim, H
    Li-rich layered oxide materials are considered promising candidates for high-capacity cathodes for battery applications and improving the reversibility of the anionic redox reaction is the key to exploiting the full capacity of these materials. However, permanent structural change of the electrode occurring upon electrochemical cycling results in capacity and voltage decay. In view of these factors, Ti4+-substituted Li2IrO3 (Li2Ir0.75Ti0.25O3) is synthesized, which undergoes an oxygen redox reaction with suppressed voltage decay, yielding improved electrochemical performance and good capacity retention. It is shown that the increased bond covalency upon Ti4+ substitution results in structural stability, tuning the phase stability from O3 to O1′ upon de-lithiation during charging compared with O3 to T3 and O1 for pristine Li2IrO3, thereby facilitating the oxidation of oxygen. This work unravels the role of Ti4+ in stabilizing the cathode framework, providing insight for a fundamental design approach for advanced Li-rich layered oxide battery materials.© 2021 Wiley-VCH GmbH
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    High‐voltage‐driven surface structuring and electrochemical stabilization of Ni‐rich layered cathode materials for Li rechargeable batteries
    (Wiley, 2020-05-04) Song, SH; Cho, M; Park, I; Yoo, JG; Ko, KT; Hong, J; Kim, J; Jung, SK; Avdeev, M; Ji, S; Lee, S; Bang, J; Kim, H
    Layered lithium–nickel–cobalt–manganese oxide (NCM) materials have emerged as promising alternative cathode materials owing to their high energy density and electrochemical stability. Although high reversible capacity has been achieved for Ni‐rich NCM materials when charged beyond 4.2 V versus Li+/Li, full lithium utilization is hindered by the pronounced structural degradation and electrolyte decomposition. Herein, the unexpected realization of sustained working voltage as well as improved electrochemical performance upon electrochemical cycling at a high operating voltage of 4.9 V in the Ni‐rich NCM LiNi0.895Co0.085Mn0.02O2 is presented. The improved electrochemical performance at a high working voltage at 4.9 V is attributed to the removal of the resistive Ni2+O rock‐salt surface layer, which stabilizes the voltage profile and improves retention of the energy density during electrochemical cycling. The manifestation of the layered Ni2+O rock‐salt phase along with the structural evolution related to the metal dissolution are probed using in situ X‐ray diffraction, neutron diffraction, transmission electron microscopy, and X‐ray absorption spectroscopy. The findings help unravel the structural complexities associated with high working voltages and offer insight for the design of advanced battery materials, enabling the realization of fully reversible lithium extraction in Ni‐rich NCM materials. © 2020 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim