Insights into Degradation Mechanisms and Optimization Strategies for High‐Voltage High‐Ni Cathode Materials

Driven by rising demands for sustainable energy storage, rechargeable Li−ion batteries (LIBs) are required to deliver elevated energy density and extended service life. High‐nickel (Ni) layered oxides stand out as promising cathode candidates for next−generation LIBs. However, structural and interfacial instabilities of high‐Ni cathodes induce severe performance degradation during long−term cycling, particularly under high‐voltage operation. This review systematically summarizes and critically examines the degradation mechanisms of high‐Ni cathode materials, with particular emphasis on atomic−scale structural insights obtained through advanced characterization techniques. Drawing on previously reported characterization studies, we highlight the evolution of O3/O1 stacking configurations and associated surface and interfacial degradation, together with progressive phase deterioration during prolonged electrochemical cycling. We further compare the reported degradation behaviors of single−crystalline and polycrystalline high‐Ni cathodes, including stress–strain evolution, planar gliding defects, cracking, and related structural instabilities. In addition, recent progress in modification strategies for high‐voltage high‐Ni cathodes is critically reviewed, with particular emphasis on approaches that reinforce intrinsic structural stability. By integrating these mechanistic insights and mitigation strategies, this review provides perspectives and rational structural design guidelines for the development of high−performance high‐Ni cathodes for next−generation advanced LIBs.