Interstitial-like B-O coordination regulation enables enhanced structural stability and Na+ transport in P2-type layered oxides for sodium-ion batteries

Abstract P2‑type layered oxide cathodes for sodium‑ion batteries (SIBs) suffer from irreversible P2→O2 phase transition and structural degradation under high voltage, leading to rapid capacity fading and a long‑standing capacity–stability trade‑off. Herein, we report a non-metallic B-O coordination regulation strategy for P2‑phase Na 2/3 Ni 1/3 Co 1/3 Mn 1/3 O 2 (NCM), where the introduced boron species form a tetrahedral interstitial-like B-O coordination. Benefiting from the strong B-O covalent interactions, this strategy effectively mitigates P2→O2 transition, enlarges Na + interlayer spacing to boost ion transport, and modulates the oxygen-related electronic structure. The optimized 3% B-doped NCM cathode delivers a high reversible capacity of 112.5 mAh g − 1 at 0.3 C with a capacity retention of 93.1% after 150 cycles, and a high-rate capacity of 101.9 mAh g − 1 at 5 C with a capacity retention of 79.1% after 400 cycles. Ex‑situ XRD indicates effective mitigation of the macroscopic P2→O2 transformation at the selected states. Density functional theory calculations reveal that B doping reduces the Na⁺ migration barrier from 2.33 eV to 1.06 eV and modulates the oxygen-related electronic states. This work highlights an optimum B-regulation window for coupling structural stability with fast Na⁺ transport in Co-containing P2 layered cathodes.