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, Na 0.67 Ni 0.23 Mn 0.67 V 0.1 O 2 @Na 3 V 2 O 2 (PO 4 ) 2 F was developed by surface-coating P2-type Na 0.67 Ni 0.23 Mn 0.67 V 0.1 O 2 with a thin layer of Na 3 V 2 O 2 (PO 4 ) 2 F to enhance both the electrochemical sodium storage and material air stability. The optimized Na 0.67 Ni 0.23 Mn 0.67 V 0.1 O 2 @5wt %Na 3 V 2 O 2 (PO 4 ) 2 F exhibited a high discharge capacity of 176 mA h g −1 within the 1.5-4.1 V range at a low current density of 17 mA g −1 . At an increased current density of 850 mA g −1 within the same voltage window, it still delivered a substantial initial discharge capacity of 112 mAh g −1 . These findings validate the significant enhancement of ion diffusion capabilities and rate performance in the P2-type Na 0.67 Ni 0.33 Mn 0.67 O 2 material conferred by the composite cathode. Graphical We propose a composite cathode material, Na 0.67 Ni 0.23 Mn 0.67 V 0.1 O 2 @Na 3 V 2 O 2 (PO 4 ) 2 F, featuring synergistic modification through doping and coating. The optimized Na 0.67 Ni 0.23 Mn 0.67 V 0.1 O 2 @5wt %Na 3 V 2 O 2 (PO 4 ) 2 F exhibited a high discharge capacity of 176 mAh g −1 within the 1.5–4.1 V range at a low current density of 17 mA g −1 . At an increased current density of 850 mA g −1 within the same voltage window, it still delivered a substantial initial discharge capacity of 112 mAh g −1 .