Synthesis and properties optimization of Na3(VOPO4)2F cathode material for sodium-ion batteries by co-precipitation method

Abstract

Na₃(VOPO₄)₂F (NVOPF) has become one of the most promising cathodes of the large-scale application of sodium-ion batteries (SIBs) owning to its high working voltage and high discharging specific capacities properties. However, the immature synthetic routes, the tedious preparation process as well as high preparation cost restrict its promotion and application to some extent. In this work, the pure NVPOF was successfully prepared by liquid phase coordination chemistry combined with co-precipitation method based on theoretical speculation. The sodium storage performances are optimized by adjusting the key process parameters such as the pH value of solutions, the catalogue of pH regulators and the solution concentrations. When pH value of the solution is 4.50, oxovanadium sulfate solution concentration lies at c_[v] = 1.5 mol L⁻¹, the as-prepared NVPOF outperforms the optimal performances. The NVPOF cathode material synthesized under the optimized conditions boasts a perfect NASICON sodium-storage structure, spherical or quasi spherical morphology. In detail, the specific capacity is 110 mAh g⁻¹ at 0.1 C and the discharging voltage is 3.86 V. The first coulombic efficiency is 91.4 %, and the specific capacity decay from 97 mAh g⁻¹ to 87 mAh g⁻¹ with 91.3 % capacity retention after 300 cycles in the half-cell system. This large-scale co-precipitation synthesis of NVOPF will provide new guidance for the development and application of cathode materials for SIBs.