Nonflammable Fluorinated Ester-Based Electrolytes for Safe and High-Energy Batteries with LiCoO2

Abstract

To further improve the energy density and safety of Li-ion batteries (LIBs), multifunctional electrolyte solvents are needed to replace conventional carbonate solvents. In this study, a nonflammable fluorinated ester, methyl 3,3,3-trifluoropropionate (MTFP), is evaluated as an electrolyte solvent for high-voltage Li batteries with the LiCoO2 positive electrode. A Li/LiCoO2 cell with an MTFP-based electrolyte exhibits superior capacity retention compared with a cell with a conventional carbonate-based electrolyte with a cutoff voltage of 4.5 V. Moreover, the LiCoO2 composite electrode with sodium carboxymethyl cellulose and styrene-butadiene rubber as binders, instead of the commonly used poly(vinylidene fluoride), can be cycled in the MTFP-based electrolyte without capacity loss or increase in polarization under high-voltage operation. The low-temperature performance and thermal stability of the LiCoO2 electrode are also improved by using the MTFP-based electrolyte. The analysis by X-ray photoelectron spectroscopy of the LiCoO2 electrode cycled in the MTFP-based electrolyte suggests that a thin and uniform passivation layer is formed on the electrode surface, resulting in excellent cyclability and thermal stability for LiCoO2. The insights related to nonflammable electrolytes contribute to the development of high-energy LIBs without sacrificing safety.