钠电池常用的钠盐溶质有哪些？

What common sodium salt solutes are used in sodium-ion batteries?

当前产业化应用钠盐分为四大品类，根据成本、循环、低温需求单独或复配使用。第一类六氟磷酸钠 NaPF6，现阶段量产主流主盐，解离度高、离子电导率优异，适配全体系碳酸酯溶剂，原料成本可控，广泛应用于户用储能、低速两轮车、电动叉车，唯一短板是遇微量水分极易水解生成酸性杂质，腐蚀电极界面。第二类双氟磺酰亚胺钠 NaFSI，热稳定、抗水解性能顶尖，能大幅减少电芯循环产气，显著拉长电池使用寿命，多用于高端长时工商业储能产品，但原料采购成本偏高。第三类四氟硼酸钠 NaBF4，低温导电性能突出，一般不作为主盐，少量复配进电解液改善北方零下二十度低温放电容量。第四类双三氟甲磺酰亚胺钠 NaTFSI，化学稳定性极强，但会持续腐蚀铝箔集流体，无法单独量产电芯，仅用于实验室新材料研发。工业量产通用最优方案以 NaPF6 为主，少量添加 NaFSI 复配，兼顾生产成本、循环寿命与量产工艺兼容性，平衡平价储能与高端长时储能不同产品定位。

Four categories of sodium salts have achieved industrialized application, used independently or blended according to cost, cycle and low-temperature demands. The first category, sodium hexafluorophosphate (NaPF6), is the mainstream primary salt for mass production at present. It features high dissociation degree and excellent ionic conductivity compatible with all carbonate solvents with controllable raw material costs, widely applied in household energy storage, low-speed two-wheelers and electric forklifts. Its only defect is easy hydrolysis upon exposure to trace moisture to generate acidic impurities that corrode electrode interfaces. The second category, sodium bis (fluorosulfonyl) imide (NaFSI), has top-tier thermal stability and hydrolysis resistance, which can drastically reduce gas generation during cycling and extend battery service life, mainly adopted for high-end long-duration industrial and commercial energy storage products yet with high raw material costs. The third category, sodium tetrafluoroborate (NaBF4), delivers outstanding low-temperature conductivity and is never used as a primary salt, only blended in small quantities to improve discharge capacity at -20℃ for northern scenarios. The fourth category, sodium bis (trifluoromethanesulfonyl) imide (NaTFSI), possesses ultra-high chemical stability but continuously corrodes aluminum foil current collectors, so it cannot be used for cell mass production and only serves laboratory material R&D. The optimal universal industrial mass-production scheme takes NaPF6 as the primary salt with a small dosage of NaFSI blended, balancing production cost, cycle life and process compatibility to fit both low-cost and high-end long-duration energy storage products.