Strain-Tolerant Layered Oxide Cathode for Sodium-Ion Batteries Enabled by a Coherent Perovskite Phase

Sodium-ion batteries are considered strong contenders for high-rate and high-power energy storage owing to their favorable ion-transport kinetics. However, under rapid Na⁺ (de)intercalation, layered oxide cathodes are prone to highly non-uniform Na⁺ extraction, which readily induces pronounced lattice strain accumulation, triggering heterogeneous phase evolution, crack formation, and progressive structural degradation, ultimately limiting rate capability and cycling stability. Despite extensive efforts devoted to compositional optimization and surface modification, an intrinsic and structure-level strategy for directly regulating rate-dependent strain evolution in layered oxide cathodes remains elusive. Here, by introducing a coherently intergrown perovskite Ca₂MnO₄ phase into a layered NaNi_1/3Fe_1/3Mn_1/3O₂ framework, a strain-tolerant composite architecture is rationally constructed. The embedded perovskite phase effectively buffers lattice deformation and constrains strain accumulation during rapid Na⁺ deintercalation, thereby stabilizing the structural evolution of the layered host. This strain-buffering design concept provides new insights into lattice-level regulation in layered oxide cathodes and opens a viable pathway toward the development of high-rate and long-life sodium-ion batteries.