Triple‐Phase Synergistic Bulk‐Surface Engineering Enables High‐Rate and Long‐Cycling P2/O3‐Based Cathode for Na‐Ion Batteries

ABSTRACT Layered oxide cathodes hold great promise for Na‐ion batteries (NIBs) but suffer from rapid performance degradation under high voltage, primarily arising from severe lattice strain, transition metal migration, and detrimental surface degradation. Here, we report a triple‐phase synergistic bulk‐surface engineering (TP‐SBSE) strategy that integrates a P2 phase, an O3 phase, and a surface disordered phase to address these challenges. In the bulk, guided by cationic potential control, we employ multielement composition modulation to construct a P2/O3 biphasic structure. The interlocking effect at the biphasic interfaces effectively suppresses structural strain and mitigates volume variations under high voltage. Meanwhile, surface reconstruction yields a protective disordered phase that not only suppresses electrode–electrolyte reactions but also alleviates anisotropic lattice strain, effectively inhibiting particle microcrack initiation and preserving bulk structural integrity. Owing to the TP‐SBSE strategy, the resulting P2/O3‐Na 0.75 Zn 0.05 Ni 0.23 Fe 0.18 Mn 0.49 Ti 0.05 O 2 (P2/O3‐NZNFMTO) cathode exhibits exceptional electrochemical performance. It delivers 80% capacity retention after 600 cycles at 1C and over 75% after 1000 cycles at 3C within 2.0 to 4.3 V, demonstrating a high rate capability and long‐term cycling stability. Moreover, this material exhibits enhanced thermal and air stability. This work presents a TP‐SBSE strategy and provides fundamental insights into developing high‐voltage, long‐life layered oxide cathodes for NIBs.