Oxidatively Stable Fluorinated Sulfones Electrolytes for High Voltage High Energy Li-Ion Batteries

Abstract

Developing a high-voltage enabling electrolyte is extremely critical for the success of the next generation high-energy density lithium-ion battery especially for electric vehicles. Material scientists have developed new cathode materials with improved specific capacity[1,2] and operating voltage (5 V vs. Li+/Li).[3,4] However, designed for a 4V-class lithium-ion chemistry, the conventional electrolyte suffers from oxidation instability on the charge cathode/electrolyte interface at high charging voltages which leads to severe transition metal (TM) dissolution and rapid capacity fading. The voltage instability of electrolyte becomes the bottleneck for the extensive application of the high voltage cathode materials. Thus, new electrolytes with elevated voltage stability has been widely explored.[5-8] Here we report a new class of fluorinated electrolytes comprising novel fluorinated sulfones including ((trifluoromethyl)sulfonyl)ethane (FMES), 1-((trifluoromethyl)sulfonyl)propane (FMPS) and 2-((trifluoromethyl)sulfonyl)propane (FMIS).[9] These compounds have been synthesized via new synthetic routes and evaluated as electrolyte materials under high voltage operation. The results indicate that sulfones with an α-trifluoromethyl group possess enhanced oxidative potential and reduced viscosity as compared to their non-fluorinated counterparts. The α-fluorinated sulfones also show enhanced wetting ability with polyolefin separator. A facile synthesis method for a reported sulfone 1,1,1-trifluoro-3-(methylsulfonyl)propane (FPMS) was also developed. With the new reaction method, large quantity of material was obtained and comprehensive electrochemical properties of FPMS as high voltage electrolyte was evaluated. Unlike the α-fluorinated sulfones, the γ-fluorinated sulfones resemble the property of the non-fluorinated ones.