The paradoxical role of rock-salt phases in high-nickel cathode stabilization: engineering a detrimental structure into a beneficial structure.

The surface phase formation of rock-salt in high-nickel layered oxide cathodes has conventionally been considered detrimental to electrochemical performance. Recent investigations, however, have revealed a more nuanced understanding wherein controlled formation of rock-salt phases during synthesis paradoxically enhances structural stability. This review critically examines the evolving paradigm of rock-salt formation in LiNixCoyMn1-x-yO2 (x ≥ 0.8) cathodes through analysis of crystallographic evolution pathways and electronic structure modifications. Synthesis-induced rock-salt phases create metastable surface structures functioning as protective interfaces against oxygen evolution, whereas electrochemically driven reconstruction during cycling triggers accelerated degradation through aggressive oxygen release. Strategic incorporation of high-valence dopants (W6+, Mo6+, and Nb5+) creates entropy-stabilized rock-salt layers with optimized lithium transport, while integration with single-crystal morphologies provides superior resistance to structural degradation by minimizing oxygen-release-prone interfaces. This review establishes design principles for next-generation high-nickel cathodes, transforming a traditionally detrimental process into a strategic enhancement mechanism for advanced lithium-ion battery applications.