Sodium ion batteries have advantages such as abundant resources, low cost, and high cost-effectiveness, and have good application prospects in the fields of electric bicycles, low-speed electric vehicles, distributed energy storage, and large-scale energy storage. The working principle of sodium ion batteries is similar to that of lithium-ion batteries, and the positive electrode material determines the energy density of sodium ion batteries. Polyanionic compounds have the advantages of high voltage, high theoretical specific capacity, and stable structure, making them one of the preferred positive electrode materials for sodium ion batteries.

Recently, the research team led by researcher Li Xianfeng, researcher Zhang Huamin and associate researcher Zheng Qiong from the energy storage Research Department of Dalian Institute of Chemical Physics made new progress in the research of polyanionic cathode materials for sodium ion batteries, and the research results were published in the Energy Bulletin of the American Chemical Society.

To improve its rate performance, optimize the performance of the entire battery, and further reduce material preparation costs and achieve large-scale material preparation, it is an urgent challenge to overcome.

Researchers have conducted a series of studies on the structural elemental regulation, sodium de intercalation mechanism, carbon composite preparation, and the construction of full and soft pack batteries of polyanionic cathode materials for sodium ion batteries, achieving efficient synthesis and application of high-performance vanadium based polyanionic compounds such as sodium trifluorophosphate, sodium vanadium fluorophosphate, and sodium vanadium phosphate.

Sodium vanadium trifluorophosphate has a three-dimensional network structure formed by the intermittent connection between the [V2O8F3] dioctahedron and the [PO4] tetrahedron, which is conducive to the rapid insertion and removal of Na+. Its theoretical energy density is 500Wh/kg, which is equivalent to the energy density of LiFePO4 in lithium-ion batteries (550Wh/kg) and has received much attention in recent years.

The research team proposed a low-temperature solvent thermal ball milling preparation method, which achieved the green and economic synthesis of high conductivity carbon coated sodium vanadium fluorophosphate (Na3V2 (PO4) 2F3). Research has found that the type of solvent and pH value play a crucial role in the morphology and product purity of Na3V2 (PO4) 2F3 during low-temperature solvothermal processes. In the acidic environment of ethanol and water mixed solvents, crystals have high surface energy and can obtain high-purity and high yield Na3V2 (PO4) 2F3. Effectively improving its ion diffusion and electron conduction capabilities. The sodium ion battery assembled with Na3V2 (PO4) 2F3 has a high specific capacity of 138mAh/g at a current of 0.5C, and can still maintain a capacity of 122mAh/g at a high current of 40C. This low-temperature solvent thermal ball milling method will provide a new strategy for the practical application of low-cost and high-performance sodium ion battery technology.