Safer Triethyl-Phosphate-Based Electrolyte Enables Nonflammable and High-Temperature Endurance for a Lithium Ion Battery

Flammable carbonate-based electrolyte greatly limits the safe application of lithium ion batteries with poor high-temperature performance. The key to developing safer electrolytes is to achieve a completely nonflammable fire safety property and meanwhile ensure a good electrochemical performance. In this study, a nonflammable electrolyte consisting of 1.0 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in triethyl phosphate (TEP) with a modified surface-film-forming additive is proposed. Against the disadvantages of concentrated electrolytes, surface-film-forming additives including vinylene carbonate (VC) and fluoroethylene carbonate (FEC) help to construct a low-concentration electrolyte with higher ionic conductivity and lower viscosity. Surface morphology and elemental analyses for the electrodes also confirm that the additive promotes the participation of lithium salt during the formation of surface film and inhibits the decomposition of TEP and the deposition of a phosphide layer. A significantly extended cycle life for cells employing several kinds of electrodes including LiNi0.8Co0.1Mn0.1O2 (NCM811), LiFePO4 (LFP), and Li4Ti5O12 (LTO) is obtained by the suggested TEP-based electrolyte. In particular, reversible cycles are realized for NCM811 up to 50 times even under 100 °C. It is believed that this nonflammable electrolyte with high-temperature endurance and good electrochemical performance is a possible candidate for the next generation of lithium ion batteries.