New Insight into Bulk Structural Degradation of High-Voltage LiCoO<sub>2</sub> at 4.55 V
Weiguang Lin, Wei Su, Ting Lin, Shiyu Wang, Jing Chen, Ang Gao, Yingchun Lyu, Dongdong Xiao, Qinghua Zhang, Lin Gu
Abstract
The aggravated mechanical and structural degradation of layered oxide cathode materials upon high-voltage charging invariably causes fast capacity fading, but the underlying degradation mechanisms remain elusive. Here we report a new type of mechanical degradation through the formation of a kink band in a Mg and Ti co-doped LiCoO 2 cathode charged to 4.55 V (vs Li/Li + ). The local stress accommodated by the kink band can impede crack propagation, improving the structural integrity in a highly delithiated state. Additionally, machine-learning-aided atomic-resolution imaging reveals that the formation of kink bands is often accompanied by the transformation from the O3 to O1 phase, which is energetically favorable as demonstrated by first-principles calculations. Our results provide new insights into the mechanical degradation mechanism of high-voltage LiCoO 2 and the coupling between electrochemically triggered mechanical failures and structural transition, which may provide valuable guidance for enhancing the electrochemical performance of high-voltage layered oxide cathode materials for lithium-ion batteries.