Facile synthesis of NaVPO4F/C cathode with enhanced interfacial conductivity towards long-cycle and high-rate sodium-ion batteries

To solve the problem of poor conductivity, monoclinic NaVPO4F with a uniform carbon coating layer is synthesized via a facile solution approach with assistance of polyvinyl pyrrolidone (PVP). On one hand, PVP acts as a surfactant, encapsulating the precursor and restraining the particle growth. On the other hand, PVP is used as carbon source, in-situ generating a uniform carbon coating layer on the surface of NaVPO4F particles. The obtained NaVPO4F/C composite shows much enhanced electronic conductivity of 4.2 × 10−2 S cm−1. As a result, the synthesized NaVPO4F/C cathode for sodium ion batteries demonstrates superior cyclic stability and rate capability, delivering a reversible capacity of 111 mAh g−1 at 0.1 C, maintaining 81.8% capacity retention after 1000 cycles at 10 C and retaining a high capacity of 68 mAh g−1 at 20 C.