Enhancement of cycling and environmental stability of O3-NaNi0.5Mn0.5O2 cathode materials by surface structure regulation

O3-type layered oxide cathodes have attracted wide attention for sodium-ion batteries (SIBs), owing to their high theoretical capacity and low cost. However, the notorious irreversible complex phase transitions and sluggish kinetics severely limit their commercial applications. Herein, surface structure regulation strategy was implemented by inducing the formation of V2O3/P2/O3 multiphase structure through ammonium vanadate treatment to improve the cycling stability of O3-NaNi0.5Mn0.5O2. The experimental results indicate that the V2O3/P2O3 multi-level structure can alleviate Jahn-Teller distortion by adjusting the Mn3+ content and suppress irreversible phase transitions. Besides, the in-situ reconstruction layer can hinder the formation of hydrated phases to enhance the environmental stability of NaNi0.5Mn0.5O2 cathode material. As a result, the modified NaNi0.5Mn0.5O2 cathode material exhibited excellent capacity retention of 74.9% after 1000 cycles at 5C (1C= 150 mAg-1), whereas the original sample only retained 42.6% of its capacity. This work provides a significant reference for designing sodium ion layered oxide cathodes with long cycle lifespan and air stability through surface structure control strategies.