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.