Fluorinated and sulfurized solid-electrolyte interface enabling durable and fast-charging graphite/LiFePO₄ pouch batteries

Safe and fast charging is important for graphite/lithium iron phosphate (Gr/LFP) batteries in the fast-growing electric vehicle industry. However, conventional carbonate-based electrolytes produce an obstructive solid-electrolyte interface (SEI), which hinders the fast charging of lithium-ion batteries (LIBs). In this study, a unique tri-methylsilyl-2-(fluorosulfonyl)difluoroacetate (TMSFS) additive was introduced to regulate the SEI of Gr/LFP batteries containing a lithium bis(fluorosulfonyl)imide-based electrolyte during fast charging. The addition of TMSFS significantly reduced the charge-transfer resistance of the anode, substantially extending the cycle life of commercial Gr/LFP batteries to over 1000 cycles at 2C rate, which was far superior to that of the baseline electrolyte (< 530 cycles). Further mechanistic studies showed that the inorganic fluorinated and sulfurized species formed on the SEI film stabilized the intermediate lithium carbonate from attack by the side-reaction products. TMSFS acts as a film-forming additive, curbing electrolyte decomposition, and fortifying the structural integrity of the electrode through the formation of a robust and low-impedance SEI film on the anode. These results provide a simple and effective strategy for combining F and S via electrolyte optimization to implement commercially safe fast-charging LIBs.