Unravelling the enhanced high‐temperature performance of lithium‐rich oxide cathode with methyl diphenylphosphinite as electrolyte additive

Shuaifeng Lou; Yulin Ma; Zhenxin Zhou; Hua Huo; Pengjian Zuo; Xinqun Cheng; Xiaohui Qu; Yunzhi Gao; Chunyu Du; Geping Yin

Index: 10.1002/celc.201800061

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Abstract

Lithium‐rich oxide cathode materials with high energy density attract much attention, however, tend to suffer from serious capacity fading during cycling, especially at elevated temperature. In this work, Methyl diphenylphosphinite (MDP) is studied as electrolyte additive for the first time, to enhance the capacity retention of lithium‐rich oxide cathode during cycling under high temperature. As a result, the cyclic stability of Li1.16Ni0.2Co0.1Mn0.54O2 cathodes at elevated temperature is improved significantly when adopting 0.2 wt.% MDP, including an enhanced Columbic efficiency and capacity retention ratio promoted from 49.7% to 93.9% after 80 cycles. Electrochemical and physical characterizations, combined with theoretical calculation, demonstrate that MDP tend to adsorb on the surface of cathode due to the interaction between the P‐O‐ species and transition metal elements, and then is oxidized preferentially than the solvent at around 3.75 V (vs. Li/ Li+), in‐situ forming a robust artificial interphase layer on the surface of cathode. The interphases can effectively inhibit the electrolyte decomposition and greatly enhance the interface stability between Li1.16Ni0.2Co0.1Mn0.54O2 and electrolyte at high voltage and high temperature.