P2/O3 Biphase Integrated With Fence-Type Superstructure Enables Robust Sodium Layered Oxide Cathodes

Layered oxides are promising cathode candidates for sodium-ion batteries (SIBs) owing to their tunable compositions and high specific capacities. However, detrimental phase transitions, Jahn-Teller (J-T) distortion, and transition-metal (TM) migration during cycling typically induce severe structural degradation and irreversible oxygen loss, ultimately resulting in rapid capacity fading. Herein, we propose a dual-scale interlayer-intralayer synergistic strategy to address these intrinsic challenges, which integrates a P2/O3 biphasic intergrowth architecture for interlayer stabilization and a fence-type superstructure with enlarged superlattice spacing for intralayer regulation within TM slabs. The intergrown P2/O3 phases generate a robust interlocking effect that alleviates strain accumulation, further suppressing undesirable phase evolution, mitigating J-T distortion, and partially restraining out-of-plane TM migration. Meanwhile, the fence-type superstructure, featuring an ultra-wide interplanar spacing, inhibits the formation of vacancy clustering driven by in-plane TM migration, thereby stabilizing the local oxygen environment and eliminating irreversible oxygen loss. Benefiting from this cooperative interlayer-intralayer regulation, the as-designed Na_0.668Li_0.1Ni_0.3Mn_0.4Ti_0.2O₂ cathode delivers quasi-solid-solution reaction behavior and highly reversible oxygen redox, along with substantially enhanced structural stability and electrochemical performance. This work highlights the critical role of dual-scale structural engineering in simultaneously modulating hierarchical structural motifs, providing a generalizable paradigm for the rational design of high-energy-density layered cathodes for SIBs.