Recent Advances and Perspectives on Single‐Crystalline Layered Oxide Cathodes for Na‐Ion Batteries

ABSTRACT Layered transition metal oxides (Na x TMO 2 ) are regarded as promising cathode materials for Na‐ion batteries because of their high capacity, compositional flexibility, and cost‐effectiveness. However, conventional polycrystalline architectures undergo pronounced performance degradation during long‐term cycling, mainly because anisotropic lattice evolution induces intergranular microcracking, which subsequently promotes electrolyte penetration, interfacial side reactions, and structural deterioration. Single crystallization has emerged as an important particle‐engineering strategy that improves the mechanical and interfacial stability of Na x TMO 2 by reducing internal grain boundaries. This review provides a systematic and comprehensive overview of recent advances in single‐crystalline layered oxide cathodes. First, the structural characteristics and capacity–kinetics trade‐offs of O3‐ and P2‐type frameworks are analyzed, linking their lattice‐dependent evolution to the advantages and remaining limitations of single crystallization. Subsequently, we systematically elaborate the main synthetic routes of single–crystalline cathodes, as well as the mechanisms whereby single crystallization modulates their structural stability and electrochemical properties. Advanced modification strategies for single–crystalline cathodes are also summarized. Finally, the discussion is extended to electrode fabrication, full‐cell applications, and practical industrial production. The remaining failure mechanisms, challenges in synthesis control, and barriers to practical implementation are examined, and perspectives are provided for developing long‐life single‐crystalline cathodes with commercial potential.