Molecular design on p–π conjugation regulation of electrolyte additives for stable low-temperature performance in lithium-ion batteries

Electrolyte additive engineering has been demonstrated as an effective strategy to improve electrochemical performance in lithium-ion batteries. However, some additives may induce battery failure during long-term cycling. We found that methyl 2,2-difluoro-2-(fluorosulfonyl)acetate (MDFSA) as an additive induces side reactions due to the coordination interaction between its ester carbonyl group and Cu current collectors. To address this issue, trimethylsilyl 2-(fluorosulfonyl)difluoroacetate (TMS-MDFSA) is designed by trimethylsilyl functionalization to regulate the molecular electron distribution. The introduction of the trimethylsilyl group weakens the p–π conjugation within the ester moiety, leading to electron redistribution around the carbonyl oxygen and a reduced tendency for coordination with the Cu surface. Moreover, the weakened Si–O bond facilitates the self-decomposition of TMS-MDFSA in the electrolyte, eliminating the Cu coordination pathway and generating active species for SEI formation. Notably, the TMS-MDFSA additive promotes the formation of an inorganic-rich solid electrolyte interphase, reducing interfacial impedance and enhancing Li + transport kinetics at low temperatures. After 220 cycles, the cell achieves a capacity retention of 84.8% at −40 °C and 0.1 C. This work provides new insights into the rational design of multifunctional electrolyte additives and the suppression of battery failure under harsh operating conditions. The coordination between methyl 2,2-difluoro-2-(fluorosulfonyl)acetate and Cu triggers Cu dissolution. Trimethylsilyl functionalization modulates p–π conjugation to facilitate the self-decomposition of trimethylsilyl 2-(fluorosulfonyl)difluoroacetate for SEI formation while suppressing Cu dissolution. Download: Download high-res image (150KB) Download: Download full-size image