Tri(trimethylsilyl) phosphate as a multifunctional additive for moisture-resistant and long-cycling sodium-ion batteries

The sodium hexafluorophosphate (NaPF₆)/carbonate solution is considered as the benchmark electrolyte for sodium-ion batteries (SIBs). However, this NaPF₆ electrolyte undergoes hydrolysis and produces acidic compounds, which deteriorate the electrolyte quality, corrode electrodes, jeopardize electrode interphases, and eventually degrade battery performance. Herein, we introduce tris(trimethylsilyl) phosphate (TMSP) as a multifunctional additive to the carbonate electrolyte. We found that 10% TMSP could effectively remove H₂O molecules and inhibit NaPF₆ hydrolysis, thus improving the electrolyte stability against moisture during the long-term storage. Furthermore, the unique structure of TMSP promotes the formation of thinner, more uniform, and inorganic-rich interphases on the Na₃V₂(PO₄)₃ (NVP) cathode and hard carbon (HC) anode. Consequently, the NVP cathode, HC anode, and full cells demonstrate excellent cycling performance. This work suggests that tailoring the electrolyte formulation can provide multiple benefits for boosting SIB performances, such as stabilizing the electrolyte and regulating the electrolyte/electrode interphase, thereby promoting long-term cycling in sodium-ion batteries.