Multiscale Failure Mechanisms of Ternary Oxide Cathode Materials for Lithium-Ion Batteries.

Ternary oxide cathodes (LiNixCoyMn1-x-yO2, NCM) have emerged as promising candidates for lithium-ion batteries (LIBs) due to high energy densities and tunable electrochemical properties. However, their structural degradation during electrochemical cycling remains challenging, with complex multiscale failure mechanisms driven by the interplay of mechanical, chemical, and electrochemical factors. These processes ultimately compromise battery activity, lifespan, and safety. To systematically unravel these failure pathways, herein, a hierarchical perspective from atomic, particle to electrode scales is adopted to dissect the origin and evolution of NCM failures. At the atomic scale, the degradation manifests as cation mixing and oxygen vacancy formation. At the particle scale, the mechanical strain accumulation induces intragranular/intergranular microcracks and particle pulverization. At the electrode scale, the failure is demonstrated by active material delamination from the current collector. Also, phase transition and side reactions across multiple scales are discussed. Furthermore, the advanced characterization techniques that enable precise identification of degradation phenomena across these scales are critically evaluated. Meanwhile, challenges in the investigation of failure mechanisms across scales are analyzed, and countermeasures are proposed. By establishing a cross-scale framework, this review aims to inspire the rational design for next-generation NCM cathode materials and even guide the recycling and reutilization of spent NCM materials for LIBs.