Effect of K and Al Co-doping on Na3V2 (PO4) 2F3 Cathode Materials

Abstract

Over the past few decades, sodium-ion batteries have gained recognition as a promising alternative to lithium-ion batteries due to their advantages of abundance, affordability, and high-power energy storage. As of now, cathode materials have emerged as the primary limiting factor in sodium-ion battery performance, considering safety, cost, cycle life, and energy density. Research in this field has mainly concentrated on layered transition metal oxides, polyanionic compounds, and hard carbon anodes as potential cathode materials for sodium-ion batteries. However, many of these materials suffer from drawbacks such as structural distortion and cyclic instability, which will restrict their practical use in sodium-ion batteries.

To address the issues of low capacity in the Na3V2(PO4)2F3 cathode material for sodium-ion batteries and the degradation of lifespan due to structural changes during charging and discharging, this paper introduces a method using the emulsion gel technique to prepare Na3V2(PO4)2F3 cathode materials doped with K at the Na sites and Al at the V sites. This method combines emulsion gelation, freeze-drying, and high-temperature calcination to synthesize the doped cathode materials. The incorporation of K ions in the material enlarges the crystal channels, enabling increased ion storage and thereby enhancing the battery's capacity. Moreover, the inclusion of Al ions preserves the material's layered structure throughout the charging and discharging process, stabilizing the crystal channel structure for the movement of electrons and ions, ultimately enhancing both the battery's capacity and charging efficiency. The cathode material Na3V2(PO4)2F3 in this scheme can achieve stable and reversible charging and discharging across a wider working voltage range, exhibiting high specific capacity and excellent rate performance. The preparation method in this scheme is straightforward and easy to follow, facilitating an increase in production rate and a reduction in production costs while maintaining high performance.