Barnes P, et al. Journal of Power Sources, 2020, 447, 227363.
Sodium hexafluorophosphate (NaPF6) is commonly used as a key electrolyte salt in sodium-ion batteries (NIBs) due to its high ionic conductivity and stability. This case study investigates the chemical stability of NaPF6-based electrolytes, focusing on the degradation mechanisms in the presence of water and the effectiveness of various additives in enhancing electrolyte stability. The study highlights two specific additives, 2,2,2-trifluoroethoxy-2,2,2-ethoxy phosphazene (FM2) and fluoroethylene carbonate (FEC), examining their impact on electrolyte degradation and cell performance. In particular, the hydrolysis of NaPF6 in the presence of water leads to the formation of hydrofluoric acid (HF), which negatively affects the electrolyte's stability. The research reveals that NaPF6-based electrolytes with trace moisture (<20 ppm) exhibit degradation leading to the formation of HF and organophosphates, reducing their shelf life. While FEC does not efficiently protect electrodes from HF exposure, FM2 demonstrates a significant ability to "scavenge" HF, thereby stabilizing the electrolyte and improving its long-term performance.
