Regulating Reversible Phase Transition at High Voltage Window on O3‐Type Layered Cathodes by Doping Zn for Sodium‐Ion Batteries

Abstract O3‐type layered cathode materials in sodium‐ion batteries exhibit high capacity for their unique crystal structures and high Na + content. However, the capacity degradation from irreversible phase transition at the high voltage window, directly limits commercial applications. Herein, Zn‐doped O3‐NaNi 1/3 Fe 1/3 Mn 1/3 O 2 (NFM) cathodes are successfully fabricated by regulating reversible phase transition with doping Zn using the high‐temperature solid‐state method. The optimal NFM‐3% Zn achieves highly efficient performance of 84.5 mAh g −1 at 10 C, and the reversible capacity is remarkably up to 83.5 mAh g −1 after 300 cycles at high voltage window of 2.0–4.2 V. The introduction of additional Zn in the TM layer enhances TM─O bonding interactions, expands alkali metal layers and increases layered crystal structure stability. Moreover, the Zn incorporation provides high electron localization, which regulates the reversible O3‐P3‐OP2‐P3’‐O3 phase transition of NFM and suppresses the random migration of TM to alkali metal layers. Combined with the results of in situ XRD and density functional theory (D calculations, the phase transition sodium storage mechanism of Zn‐doped NFM cathode is investigated in detail. This study provides a modification strategy for O3‐type layered cathode materials to improve performance at the high voltage window for sodium‐ion batteries.