Modification of the morphology of Na3V2(PO4)2F3 as cathode material for sodium-ion batteries by polyvinylpyrrolidone

Abstract NASICON-type Na3V2(PO4)2F3 (NVPF) is proposed to be a potential cathode material for sodium-ion battery because of its good structural stability, relatively high capacity and voltage platform. Nonetheless, the poor-rate performance, resulting from its low conductivity, has become a massive obstacle to its practical application. In this work, carbon coating together with morphology controlling were introduced to solve the issue of NVPF. This experiment used a hydrothermal method to prepare Na3V2(PO4)2F3@C (NVPF@C) and explored the impact of surfactants (polyvinylpyrrolidone (PVP)) on the positive material performance of sodium-ion battery. Through various characterisation, NVPF@C compared its performance with that of untreated products, and verified that appropriate surfactant modification could enhance the performance of the electron conduction and sodium ion diffusion, thus effectively improved the performance of NVPF. Through comparison, it was found that appropriate surface modification with PVP can achieve the effects of specific crystal surface exposure and clusters of porous micron ball structure, and improve the electrochemical performance of NVPF best. Under the charge and discharge ratio of 0.2C, its initial reversible capacity was 127.8 mA h g−1. After 100 cycles, its discharge capacity was 106.1 mA h g−1, and the cycling retention rate reached 82.8%. Compared to the original NVPF, its performance has been dramatically improved.