Mechanistic Insights into Tris(trimethylsilyl) Phosphite as an Electrolyte Additive: Acid Scavenging and Triggering of FEC Degradation

Tris(trimethylsilyl) phosphite (TMSP) has attracted considerable attention as an efficient functional electrolyte additive for lithium-ion batteries (LIBs). Its ability to enhance the stability of the solid electrolyte interphase (SEI) by scavenging hydrofluoric acid (HF) has been demonstrated. However, the unclear understanding of the TMSP acid scavenging mechanism and its potential effect on electrolyte component degradation has severely limited the capacity of TMSP as a high-performance electrolyte additive. In this study, we employed computational methods to clarify the HF scavenging mechanism of TMSP and explore its triggering of fluoroethylene carbonate (FEC) degradation pathways. Our results reveal that the phosphorus oxygen double bond in TMSP is the key structural feature for the HF scavenging. HF is neutralized through nucleophilic addition to the phosphorus oxygen double bond, followed by proton transfer. The TMSP further triggers a series of continuous acid scavenging reactions. Additionally, we found that PF4OH, a byproduct of these reactions, acts as a catalyst in the decomposition of FEC. This process leads to the regeneration of HF, consequently driving the degradation of FEC.