Trifluoroacetic Anhydride: A Dual-Function Electrolyte Additive for Cycle-Life Extension and Flame Retardancy in Li-Metal Batteries

Lithium batteries are pivotal for modern energy storage, yet their performance and safety are critically influenced by electrolyte stability. This study systematically investigates three structurally similar fluorinated anhydrides, difluoroacetic anhydride (DFAA), trifluoroacetic anhydride (TFAA), and pentafluoropropionic anhydride (PFPA), as multifunctional electrolyte additives for lithium metal batteries. Electrochemical evaluations reveal that the addition of 1 wt% TFAA significantly enhances the cycling stability of both LiFePO 4 (LFP) and LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622) cathodes. After 400 cycles at 1 C, LFP||Li cells with TFAA retain 79.6% capacity, substantially higher than the 59.4% observed with the baseline electrolyte. Similarly, NCM622||Li cells exhibit a capacity retention of 64.4% with TFAA, compared to only 45.3% for the reference. Moreover, TFAA improves rate capability and extends the electrochemical stability window to 4.1 V. XPS and TEM analyses confirm that TFAA facilitates the formation of a thin, uniform, and fluorine-rich solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI), which effectively suppresses electrolyte decomposition and interfacial side reactions. Additionally, TFAA demonstrates notable flame-retardant properties and acts as an effective H 2 O scavenger, thereby enhancing battery safety. These findings underscore TFAA as a promising multifunctional additive for developing high-performance, long-cycling, and safer lithium metal batteries.