Simultaneous enhancement of Na-ion diffusion and electronic conduction in Na3V2(PO4)2F3 cathode material by Ga doping and N-doped carbon

Abstract

Na3V2(PO4)2F3 (NVPF) polyanion cathode offers high structural stability and fast Na+ migration for sodium-ion batteries (SIBs), but it suffers from low intrinsic electronic conductivity and sluggish ion kinetics, as well as unavoidable fluorine loss during synthesis. Herein, we report a dual-modified NVPF cathode material (NC@NVGPF) through simultaneous Ga doping and N-doped carbon coating. Density functional theory calculations demonstrate that Ga doping not only reduces Na-ion migration energy barriers by 19.6% (0.56 → 0.45 eV) but also decreases the bandgap by 40% (2.37 → 1.43 eV), significantly enhancing ionic and electronic transport properties. Structural characterization confirms Ga doping stabilizes the NVPF framework by strengthening V–F bonds (1.89 → 1.62 Å), effectively suppressing fluorine loss and Na3V2(PO4)3 phase formation. Electrochemically, NC@NVGPF delivers 125.5 mAh g−1 at 0.2C and 90.1% capacity retention after 200 cycles at 1C. When assembled into a full cell coupled with commercialized hard carbon, it achieves a reversible capacity of 105.5 mAh g−1 with 92.9% capacity retention over 100 cycles at 1C. These findings reveal that the synergistic action of Ga doping and N-doped carbon coating offers a promising pathway to optimize fluorinated polyanionic cathodes for SIB application.