Tuning Na Occupation and Annealing Temperature on Na Diffusion Pathways in P2-Type NaNiMnO for Sodium-Ion Batteries by Ab Initio Calculations.

The NaNiMnO cathode material draws ongoing interest owing to its considerable specific capacity along with its elevated average operating voltage. However, its application is limited by weak rate performance and quick capacity fading. In this study, a series of NaNiMnO ( = 0.65, 0.70, 0.75, 0.80) cathode materials are prepared by the solid-phase method based on an orthogonal experiment. The optimum preparation process is investigated by optimizing factors such as Na content, calcination temperature, calcination time, and heating rate. The Na/Na ratio is adjusted, and the Na at different sites are rearranged to reduce the Na/vacancy ordering by changing the Na content on the basis of process optimization. Owing to the fast migration kinetics of Na sites, experimental results indicate that the P2-NaNiMnO cathode material, which has Na occupying more thermodynamically stable Na sites, demonstrates superior battery performance. High initial discharge specific capacity (157.2 mAh g) along with favorable cycle performance of the NaNiMnO cathode material can be achieved by modifying the Na site occupancy and optimizing the experimental conditions. Together with the microscopic control of Na occupancy, this novel orthogonal experiment design offers a fresh perspective and approach to a thorough comprehension of cathode materials for sodium-ion batteries.