Multiple Surface Optimizations for a Highly Durable LiCoO<sub>2</sub> beyond 4.6 V
Zijian Li, Haocong Yi, Hengyu Ren, Jianjun Fang, Yuhao Du, Wenguang Zhao, Hui Chen, Qinghe Zhao, Feng Pan
Abstract
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.