Understanding the Degradation Mechanisms of LiNi0.5Co0.2Mn0.3O2 Cathode Material in Lithium Ion Batteries

Authors

  • Sung-Kyun Jung,

    1. Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul, Republic of Korea
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  • Hyeokjo Gwon,

    1. Department of Materials Science and Engineering, KAIST (Korea Advanced Institute of Science and Technology), Daejeon, Republic of Korea
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  • Jihyun Hong,

    1. Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul, Republic of Korea
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  • Kyu-Young Park,

    1. Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul, Republic of Korea
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  • Dong-Hwa Seo,

    1. Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul, Republic of Korea
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  • Haegyeom Kim,

    1. Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul, Republic of Korea
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  • Jangsuk Hyun,

    1. Battery Materials R&D Team, Samsung Fine Chemicals, Daejeon, Republic of Korea
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  • Wooyoung Yang,

    1. Battery Materials R&D Team, Samsung Fine Chemicals, Daejeon, Republic of Korea
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  • Kisuk Kang

    Corresponding author
    1. Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul, Republic of Korea
    2. Center for Nanoparticle Research, Institute for Basic Science (IBS) and Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul, Republic of Korea
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Abstract

LiNixCoyMnzO2 (NCM, 0 ≤ x,y,z < 1) has become one of the most important cathode materials for next-generation lithium (Li) ion batteries due to its high capacity and cost effectiveness compared with LiCoO2. However, the high-voltage operation of NCM (>4.3 V) required for high capacity is inevitably accompanied by a more rapid capacity fade over numerous cycles. Here, the degradation mechanisms of LiNi0.5Co0.2Mn0.3O2 are investigated during cycling under various cutoff voltage conditions. The surface lattice structures of LiNi0.5Co0.2Mn0.3O2 are observed to suffer from an irreversible transformation; the type of transformation depends on the cutoff voltage conditions. The surface of the pristine rhombohedral phase tends to transform into a mixture of spinel and rock salt phases. Moreover, the formation of the rock salt phase is more dominant under a higher voltage operation (≈4.8 V), which is attributable to the highly oxidative environment that triggers the oxygen loss from the surface of the material. The presence of the ionically insulating rock salt phase may result in sluggish kinetics, thus deteriorating the capacity retention. This implies that the prevention of surface structural degradation can provide the means to produce and retain high capacity, as well as stabilize the cycle life of LiNi0.5Co0.2Mn0.3O2 during high-voltage operations.

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