Self-Regulating Sodium-Ion Battery Materials: From Phase Reconstruction to Functional Activation

Sodium-ion batteries are advancing toward practical deployment, yet their long-term durability is governed not by static material properties but by the coupled evolution of the lattice, interface, and electrolyte environments under operating conditions. However, a systematic consolidation of these dispersed mechanistic insights is still lacking. This review introduces a unified self-regulation framework in which structural and chemical changes remain confined, reversible, and functionally aligned with electrochemical transport. Evidence is organized along three axes: lattice and phase evolution in layered oxides, where controlled slab glide, moderated Na-vacancy ordering, and stabilized oxygen participation narrow phase windows; interphase chemistry and mechanics, emphasizing inorganic-rich, self-renewing interfacial architectures that sustain ion transport and limit dissolution; and electrolyte-materials coupling, where solvation structure, concentration regimes, and targeted additives steer interphase reconstruction and near-surface transport. The scope spans major cathode families and self-buffering anodes, with electrolytes treated as purposeful enablers. From these insights, we distill design rules linking operando signatures to composition and processing choices and outline opportunities for model-guided optimization and data-driven discovery. This framework provides a materials-first roadmap toward programmable, durable sodium-ion batteries operating reliably under practical constraints.