High‐Entropy Doped P'2 Mn‐Based Layered Oxide with Superior Stability and High Capacity for Sodium‐Ion Batteries

Abstract P'2‐Na x MnO 2 (NMO) features an ultra‐high specific capacity in sodium‐ion batteries, which, however, suffers from a fast capacity decay. To improve the stability, a high‐entropy doped P'2‐Na 0.59 Mn 0.90 Ti 0.02 Cu 0.02 Ni 0.02 Co 0.02 Fe 0.02 O 1.95 F 0.05 (NMHE 0.1 OF) is developed to lessen the Jahn‐Teller distortion and address the multiple phase transition issue. Physicochemical characterizations reveal that the NMHE 0.1 OF yields a lower anisotropy in the Mn─O bond than does the undoped NMO. Theoretical calculations indicate that the cation doping enhances the coordination ability of oxygen and the F doping breaks the electronic symmetry of Mn. The in situ X‐ray diffraction result reveals that the NMO experiences a more abrupt and irreversible OP4‐P'2‐P″2 tri‐phase transition; and the NMHE 0.1 OF features a mild and reversible OP4‐P'2 bi‐phase transition, which originates from the alleviation in the contraction/expansion of the transition metal slabs evidenced by ex situ extended X‐ray absorption fine structure. The bi‐phase transition favors the compatibility between the NMHE 0.1 OF and the ether‐based electrolyte at high voltages. As a result, the NMHE 0.1 OF yields a superior cyclability (97.8% capacity retention after 100 cycles at 100 mA g −1 ) with a notable specific capacity of 224 mAh g −1 at 10 mA g −1 . This work provides an effective strategy for the rational design of cathode materials with high capacity and superior stability.