Quantitative Phase Tuning and Interlayer Anchoring Stabilize Biphasic High‐Entropy Cathodes for Sodium‐Ion Batteries

ABSTRACT The development of layered oxide cathodes for sodium‐ion batteries is hindered by irreversible phase transitions and substantial volume changes at high voltages. While P2/O3 biphasic structures can mitigate these issues, achieving precise control over phase composition and understanding the underlying stabilization mechanisms remain challenging. Herein, we propose a synergistic regulation strategy integrating cationic potential design and thermal processing optimization. Using a high‐entropy layered oxide Na 0.75 Ni 0.29 Zn 0.05 Cu 0.06 Mn 0.6‐x Ti x O 2 as a model, we establish a quantitative correlation between Ti 4+ content and the P2/O3 phase ratio, achieving continuous tuning from 0% to 100% O3 phase. Further refinement via calcination temperature yields an optimal P2:O3 ratio of 72.7:27.3. This optimally designed cathode delivers a high‐rate capability (76.2 mAh g −1 at 5 A g −1 ) and superior cycling stability (77.5% capacity retention after 200 cycles). Operando XRD and DFT calculations reveal an “interlayer anchoring mechanism” at the phase boundary, where strong ionic bonding (e.g., Ti‐O) suppresses transition metal layer sliding, guiding a highly reversible phase evolution and reducing the volume change to 7.6%, significantly lower than that of the single‐phase counterpart (12.7%). This work provides a quantitative “composition–process–phase–performance” design principle for advanced biphasic cathode materials.