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_0.75Ni_0.29Zn_0.05Cu_0.06Mn_0.6-xTi_xO₂ as a model, we establish a quantitative correlation between Ti⁴⁺ 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.

Keywords

interlayer anchoring / layered transition metal oxide / P2/O3 biphasic cathode / sodium-ion batteries

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2026 The Author(s). Carbon Neutralization published by Wenzhou University and John Wiley & Sons Australia, Ltd.