Sn-doped Na3V2(PO4)2F3 co-modified with reduced graphene oxide coating toward enhanced sodium-ion storage performance

Na 3 V 2 (PO 4 ) 2 F 3 (NVPF) is a promising cathode material for sodium-ion batteries owing to its impressive theoretical capacity, elevated operating voltage, and stable structure. However, its practical utilization remains limited owing to its poor electronic conductivity. To overcome this issue, an Sn-doped and reduced graphene oxide (rGO)–coated NVPF cathode is successfully prepared using the sol–gel method. Sn substitution moderately widens the lattice spacing, facilitating intrinsic electronic conductivity, while rGO coating provides continuous conductive pathways along the particle surfaces, suppressing polarization and enhancing external electron transport. Herein, the optimized Na 3 V 1.93 Sn 0.07 (PO 4 ) 2 F 3 @rGO (NVSnPF-0.07@rGO) cathode reached a specific capacity of 123.0 mAh g −1 at 1 C, with a rate capability of 74.4 mAh g −1 at 30 C, which is superior to those of the unmodified NVPF cathode. The capacity retention remains at 80.7 % after 2500 cycles at 30 C. Density functional theory analysis reveals that Sn doping is beneficial for improving the electrical conductivity of NVPF. Finally, the NVSnPF-0.07@rGO//HC (hard carbon) full cell reaches a discharge output of 92.2 mAh g −1 at 1 C after long-term cycling and a Coulombic efficiency of ∼100 %. The evidence presented in this study provides a framework for advancing the functional properties of cathode materials.