Internal Vanadium Doping and External Modification Design of P2-Type Layered Mn-Based Oxides as Competitive Cathodes toward Sodium-Ion Batteries.

P2-type layered manganese-based oxides have attracted considerable interest as economical, cathode materials with high energy density for sodium-ion batteries (SIBs). Despite their potential, these materials still face challenges related to sluggish kinetics and structural instability. In this study, a composite cathode material, NaNiMnVO@NaVO(PO)F was developed by surface-coating P2-type NaNiMnVO with a thin layer of NaVO(PO)F to enhance both the electrochemical sodium storage and material air stability. The optimized NaNiMnVO@5wt %NaVO(PO)F exhibited a high discharge capacity of 176 mA h g within the 1.5-4.1 V range at a low current density of 17 mA g. At an increased current density of 850 mA g within the same voltage window, it still delivered a substantial initial discharge capacity of 112 mAh g. These findings validate the significant enhancement of ion diffusion capabilities and rate performance in the P2-type NaNiMnO material conferred by the composite cathode.