Achieving Zero Phase Transition in P2‐Type Layered Oxides via Targeted Chemical Design for Zero‐Strain Sodium Storage

Abstract

ABSTRACT P2‐type layered oxide cathodes dominate sodium‐ion batteries (SIBs) due to exceptional sodium ion kinetics. However, longstanding phase transitions (e.g., P2‐to‐O2) not only compromise this inherent kinetic advantage but also cause severe stress strain undermining structural stability. Here, we propose a stage‐specific chemical design that targetly addresses de‐sodiated interlayer O 2− repulsion, the structural origin of phase transitions in P2 cathodes. The designed Na 0.67 Ni 0.05 Fe 0.05 Ti 0.05 Cu 0.2 Mn 0.65 O 2 (NFTCM) cathode shows a record Na‐layer spacing (3.67 Å) with reduced negative charge on oxygen ions, maximally lowering O 2− –O 2− repulsion during the entire desodiation process. As evidenced by in situ X‐ray diffraction, the NFTCM cathode shows a true zero‐phase‐transition behavior with a record‐low volume variation of 0.062% upon cycling. This stable, zero‐strain Na ions storage behavior contributes to exceptional rate capability (121 mA h/g at 10C) and remarkably stable cycling, retaining 93.7% capacity after 600 cycles. Furthermore, operando neutron diffraction data indicate that the eliminated phase transition also enables a robust oxygen framework, a crucial factor in stabilizing the ion storage process of layered oxides.