Unravelling the Enhanced High-Temperature Performance of Lithium-Rich Oxide Cathode with Methyl Diphenylphosphinite as Electrolyte Additive

Lithium-rich oxide cathode materials with high energy density attract much attention, however, they tend to suffer from serious capacity fading during cycling, especially at elevated temperature. Here, 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 calculations, demonstrate that MDP tends to adsorb on the cathode surfacedue to the interaction between the P-O-species and transition-metal elements, and then is oxidized preferentially at around 3.75 V (vs. Li/Li+), insitu forming a robust artificial interphase layer on the surface of the cathode. The interphases can effectively inhibit the electrolyte decomposition and greatly enhance the interface stability between Li1.16Ni0.2Co0.1Mn0.54O2 and the electrolyte at high voltage and high temperature.