In situ functionally utilize surface residual lithium of Co-free Li-rich layered oxides

As the candidate cathode material of next-generation lithium-ion batteries (LIBs), Li-rich layered oxides (LLOs) suffer from the problems of surface residual lithium and own insufficient performance as an ionic and electronic conductor. Herein, we propose a strategy for in situ utilization of the residual lithium to form a functionalized sulfur-containing surface coating layer for Co-free LLOs by designated consumption of the residual lithium compounds (Li2CO3 and LiOH) with a simple sulfur treatment. The layer significantly improves the lithium-ion diffusion kinetics at high current rates and inhibits the growth of charge transfer resistance. The results of composition and structure characterization prove that the layer mainly containing Li2SO4 guides the favorable evolution of particles’ bulk crystal structure during the cycle. The modified sample exhibits a higher first coulombic efficiency of 84.4%, excellent rate capabilities, and superior cycle capacity retention of 93.3% after 300 cycles at 250 mA g−1.