Multiple Surface Optimizations for a Highly Durable LiCoO2 beyond 4.6 V

Abstract Recently, lots of researches have focused on enhancing the structure stability of LiCoO 2 (LCO) at a cutoff voltage of 4.6 V (vs Li/Li + ) at room temperature. However, the high temperature (≥45 °C) performances are more significant for practical applications. Herein, the mechanism of unsatisfactory structure stability of LCO at 45 °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 °C is mainly due to two aspects: i) the promoted bulk Li + ion diffusion kinetics at 45 °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 °C blocks the Li + ion transport channels. Surface optimizations, including the anions (F − and PO 4 3− ) and cations (Al 3+ ) 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 °C and beyond 4.6 V. A new insight is provided here for developing more advanced and practical high‐voltage LCO.