Paradoxical Role of Rock-Salt Phases in High-Nickel Cathode Stabilization: Engineering Detrimental to Beneficial

Abstract

The surface phase formation of rock salt in high-nickel layered oxide cathodes has generally been considered detrimental to electrochemical performance. However, recent investigations have revealed a more nuanced understanding of this phenomenon, wherein the controlled formation of rock salt phases during synthesis can paradoxically enhance the structural stability. This review critically examines the evolving paradigm of rock-salt formation in LiNixCoyMn1-x-yO2 (x ≥ 0.8) cathodes through a comprehensive analysis of crystallographic evolution pathways, reaction kinetics, and electronic structure modifications. It has been demonstrated that the synthesis-induced rock-salt phases create metastable surface structures that function as protective interfaces, whereas electrochemically driven reconstruction during cycling triggers degradation through oxygen evolution and electrolyte decomposition. Advanced characterization revealed that the strategic incorporation of high-valence dopants created entropy-stabilized rock-salt layers with optimized lithium transport pathways. Integration with single-crystal morphologies provided superior resistance to structural degradation compared with conventional polycrystalline materials. By reconciling the paradoxical role of rock salt phases, this study establishes design principles for next-generation high-nickel cathodes, thereby transforming a traditionally detrimental process into a strategic enhancement mechanism for lithium-ion batteries.