Partially fluorinated linear carboxylate esters employed as co-solvents for high-voltage lithium-ion batteries

A strategy of a series of partially fluorinated linear carboxylate esters (FLCEs) employed as a co-solvent to prepare high voltage, nonflammable electrolytes in LiNi0.5Mn1.5O4 (LNMO) lithium-ion batteries is proposed. This work systematically studies the physical, chemical, and electrochemical properties of these FLCEs solvents, and then investigates the electrochemical performances of the high-voltage LNMO batteries with the FLCEs-containing electrolytes. Our results show that except for methyl 3,3,3-trifluoropropanoate (F1) has high solubility of lithium salt LiPF6, other FLCEs solvents cannot dissolve 0.1 mol L−1 LiPF6. In view of the chemical stability results, only using the FLCEs single solvent cannot form stable interfacial film on Li metal, thus they cannot be used as a single solvent, and must be mixed with other solvents to prepare the electrolytes. The calculation and experimental results display that the FLCEs have both high oxidation potentials and high reductive potentials, which infers that they are hard to be oxidized and easy to be reduced, respectively. The charge-discharge results show that the F1-based electrolyte exhibits non-flammable, good wettability and excellent cyclability in the environment of high voltage batteries. This work confirms that FLCEs, e.g., F1, are promising cosolvents for high voltage lithium-ion battery electrolytes with enhanced safety and longevity.