Multiple Surface Optimizations for a Highly Durable LiCoO₂ beyond 4.6 V

Recently, lots of researches have focused on enhancing the structure stability of LiCoO2 (LCO) at a cutoff voltage of 4.6 V (vs Li/Li+) at roomtemperature. However, the high temperature (>= 45 degrees C) performances are more significant for practical applications. Herein, the mechanism of unsatisfactory structure stability of LCO at 45 degrees C via comparing a commercial LCO (C-LCO) and a surface optimized LCO (O-LCO) is revealed first. The deteriorated structure stability of LCO at 45 degrees C is mainly due to two aspects: i) the promoted bulk Li+ ion diffusion kinetics at 45 degrees C leads to a higher state of charge for the charged LCO, which triggers more side reactions; ii) the more prominent surface structure collapse at 45 degrees C blocks the Li+ ion transport channels. Surface optimizations, including the anions (F- and PO3-4) and cations (Al3+) surface modulation and a subsurface spinel reinforcement, are comprehensively applied to alleviate the side reaction and structure collapse issues of O-LCO, leading to a high reversible discharge capacity of 238 mAh g(-1), as well as an obviously enhanced cycle and floating stability at 45 degrees C and beyond 4.6 V. A new insight is provided here for developing more advanced and practical high-voltage LCO.