Regulation of the electrochemical performance of Na3V2(PO4)2F3 as an Na storage material through electron redistribution by Bi-doping

Heteroatom doping in Na 3 V 2 (PO 4 ) 2 F 3 (NVPF) is popular because it can effectively enhance electrochemical performance characteristics. However, a deep understanding of how different heteroatom dopants from synthesis to the charging/discharge process is still lacking. Herein, we show that doping of NVPF with Bi affects the electron density around V, and that electron migration is facilitated by the effect of the anions. During heat treatment, the binding energy of Bi 3+ is lowered, whereas that of V 3+ /V 4+ remains relatively stable. Although the crystal structure is stable after Bi-doping, the morphology, the carbon content and the ratio of sp 3 -and sp 2 -hybridized carbon atoms are slightly modified. The electrochemical performance is improved after Bi-doping due to increased diffusion coefficient of Na + ions, pseudo-capacitance contribution and the involved in the electron of Bi. Moreover, ex -XRD, ex -XPS, CV and EIS spectra are applied to analyze the variation in charging/discharging performance with cycling. Although the crystal structure remains rigid, the redox peaks, electrochemical reaction resistance and solid electrolyte interphase film are modified during cycling. The binding energy of Bi 3+ changes more markedly than that of V because it is involved in the reaction. This study improves our understanding of the effects of heteroatom doping in the NVPF structure, providing guidance for the selection of suitable heteroatoms. • Doping of NVPF with Bi affects the electron density around V. • Binding energy of Bi 3+ is lowered, whereas that of V 3+ remains relatively stable. • Bi 3+ binding energy changes more markedly than V 3+ ‘s due to involvement.