Degradation and Failure Mechanisms of Lithium/LiNi_<i>x</i>Co_<i>y</i>Mn_{1–<i>x</i>–<i>y</i>}O₂ Batteries

Lithium (Li)/LiNi_xCo_yMn_1-x-yO₂ (NCM) batteries are considered one of the most promising battery technologies for next-generation energy storage, but their commercial viability is still hampered by rapid capacity decay and safety concerns. Recently, the mechanistic understanding of Li/NCM battery degradation and failure processes has made significant progress thanks to advances in battery diagnostics and analysis. Herein we comprehensively review the current understanding of Li/NCM battery degradation as a function of the type of electrode materials, electrolytes, packaging formats, and cycling conditions, and discuss the degradation mechanisms related to the interplay between the Li metal anode and the NCM cathode. We also review the safety threats and eventual failure of Li/NCM batteries and their root causes. Moreover, we provide our perspectives on the future research necessary to gain a more complete understanding of the degradation and failure of Li/NCM batteries.