Publication

Abstract : Doping in the transition metal site of Na3V2(PO4)2F3 (NVPF) is considered as a novel strategy to leverage the electrochemical performance of polyanionic fluorophosphates. Here in we report a dual doping strategy by introducing aliovalent and isovalent dopants in to the V site to improve the cycling stability and rate performance of NVPF. The impact of different concentrations of Cr and Mg in V lattice on structural, morphological, and surface properties were investigated and optimum dopant concentration which deliver superior electrochemical performance was identified. The effect of mixed solvent electrolyte on the electrochemistry of dual-doped NVPF_Cr0.05Mg0.05 was analysed, the better performance of PC:DMC; FEC mixed solvent was justified with the help of impedance spectroscopy and differential capacity curves. Moreover, the ex-situ XPS analysis of the electrodes from the mixed electrolyte system at different stage of sodiation and desodiation reveals a unique interfacial mechanism. At de-sodiated stage, the interface mechanism resulting from an electrostatic forces arises from polarity of solvent molecules was observed. This induces dipole-like charges on the fluorine atoms of PVDF polymer chain that can connect with V5+ on the surface of dual-doped NVPF_Cr0.05Mg0.05 aiding for improved electrochemical performance.