Fluorinated Alkyl Substituted Sulfones As Electrolytes for High Voltage Lithium-Ion Battery

Abstract

In an effort to enhance the energy and power density of Li-ion battery technology to facilitate the commercialization of electric vehicles, material researchers have developed new cathode materials with improved specific capacity [1] and operating voltage (5 V vs. Li+/Li).[2] However, the state-of-the-art electrolyte containing 1.2 M lithium hexafluorophosophate (LiPF6) in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC)/ethyl methyl carbonate (EMC) decomposes at above 4.5 V vs. Li+/Li which prevents the extensive use for the high voltage cathode materials. [3] Thus, the exploration of new electrolytes with elevated voltage stability has been actively pursued. [2] In this paper, we present a novel electrolyte candidate of fluorinated sulfones for high voltage Li-ion battery. Aided by DFT computation, fluorinated sulfones with various chemical structures (trifluoromethyl)sulfonylethane (FMES), 1-(trifluoromethyl)sulfonylpropane (FMPS) and 2-(trifluoromethyl)sulfonylpropane (FMIS) were designed, synthesized and characterized with analytical methods including NMR, GC-MS and FT-IR and their oxidation stability were examined by a floating method using LiNi0.5Mn1.5O4/Li cell. Sulfone with trifluoromethyl (-CF3) substitution at alpha position possesses enhanced oxidative stability and reduced viscosity as compared to their non-fluorinated counterparts. The alpha-substituted fluorinated sulfones also showed improved wetting ability with PE/PP separators. A facile method for the synthesis of 1,1,1-trifluoro-3-(methylsulfonyl)propane (FPMS), which enabled us to produce adequate amount of FPMS for electrolyte testing, was also developed. Unlike alpha-substituted fluorinated sulfones, the gamma-substituted fluorinated sulfones resemble the properties of their non-fluorinated ones.