High-valence Ta5+ doping in Na3V2(PO4)2F3/C cathodes for enhanced sodium storage

Na 3 V 2 (PO 4 ) 2 F 3 (NVPF), as a NASICON-type cathode material, has attracted considerable attention for sodium-ion batteries owing to its particular three-dimensional framework and fast Na + transport channels. Moreover, its high operating voltage and excellent cycling stability make NVPF a highly competitive cathode candidate for sodium-ion batteries. These structural merits make NVPF attractive for sodium-ion storage, but its practical performance is still hindered by poor intrinsic electron transport. Herein, Ta 5+ doping is employed as a high-valence cation regulation strategy to modulate the local structure and electrochemical kinetics of Na 3 V 2 (PO 4 ) 2 F 3 /C cathode materials. The optimized NVPF-Ta-0.05/C sample maintains the main NVPF framework while inducing local lattice regulation and electronic-structure modulation. DFT calculations further reveal that Ta 5+ substitution narrows the band gap and modifies the electronic structure of NVPF/C, which is beneficial for electronic transport. Compared with the pristine sample, NVPF-Ta-0.05/C delivers enhanced rate capability and cycling stability, achieving reversible capacities of 121.65 mAh g −1 at 0.1 C and 61.07 mAh g −1 at 30 C, with 93.47% capacity retention after 860 cycles at 30 C. Electrochemical analyses based on CV, EIS and GITT demonstrate improved charge-transfer behavior and Na + diffusion kinetics after Ta 5+ doping. This work provides useful insight into high-valence cation regulation of NVPF-based cathode materials for sodium-ion batteries.