Interfacial Failure Cascade and Modulation Strategies for Layered Oxide Cathodes in Sodium-Ion Batteries

Layered transition-metal oxides (Na_xTMO₂) are among the most promising cathode candidates for sodium-ion batteries, yet their interfacial degradation under high voltage, deep desodiation, and humid environments remains the central bottleneck to commercialization. Here we argue that interfacial failure of layered cathodes is not a collection of isolated events but a coupled failure cascade in which chemical, structural, and mechanical factors amplify one another along a causal chain-surface residual alkali and oxygen release, heterogeneous phase transitions and surface reconstruction, stress concentration and crack propagation, and finally electrolyte infiltration with self-catalyzed formation of fresh interfaces. Starting from this cascade, we extract the corresponding modulation targets and, organized along the atomic-nano-micro length scale, survey single-axis strategies that include pillar-ion pinning, in situ conversion of residual alkali, gradient and epitaxial coatings, intergrown heterointerfaces, multifunctional coatings, and concentration-gradient particles. We then synthesize cross-scale synergistic paradigms-coating-plus-doping cascades, mechano-electrochemical coupling, dynamically stable interfaces under wide-temperature and high-voltage operation, and cathode-electrolyte interphase (CEI) engineering-and show that interface modulation is shifting from passive isolation toward active regulation. We close by distilling actionable design principles and outlining prospects for responsive interfaces and rational design.