Reorganizing electronic structure of Li₃V₂(PO₄)₃ using polyanion (BO₃)³⁻ : towards better electrochemical performances

Doping modification of electrode materials is a sought-after strategy to improve their electrochemical performance in the secondary batteries field. Herein, polyanion (BO₃)³⁻-doped Li₃V₂(PO₄)₃ cathode materials were successfully synthesized via a wet coordination method. The effects of (BO₃)³⁻ doping content on crystal structure, morphology and electrochemical performance were explored by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). All the as-prepared samples have the same monoclinic structure; among them, Li₃V₂(PO₄)_2.75(BO₃)_0.15 sample has relatively uniform and optimized particle size. In addition, this sample has the highest discharge capacity and the best cycling stability, with an initial discharge capacity of 120.4 mAh·g⁻¹, and after 30 cycles at a rate of 0.1C, the discharge capacity still remains 119.3 mAh·g⁻¹. It is confirmed that moderate polyanion (BO₃)³⁻ doping can rearrange the electronic structure of the bulk Li₃V₂(PO₄)₃, lower the charge transfer resistance and further improve the electrochemical behaviors.