Rational Design of Electrolytes for Long-Term Cycling of Si Anodes over a Wide Temperature Range

A silicon (Si) anode is a high-capacity alternative for carbonaceous anodes in lithium ion batteries. However, a large volume change during cycling and continuous side reactions with the electrolyte significantly limit its applications. We designed a localized highconcentration electrolyte using 1H,1H,5H-octafluoropentyl 1,1,2,2-tetra-fluoroethyl ether (OTE) as a diluent with the desired molecular structure tailored for a Si anode operating over a wide temperature range. This electrolyte exhibits an optimized ion solvation structure and enabled better cycling stability of Si anodes over a wide temperature range. Full cells with Si/graphite composite anodes and LiNi0.5Mn0.3Co0.2O2 cathodes retained 80% of their capacity after 500 cycles in 1.74 M lithium bis(fluorosulfonyl)imide in dimethyl carbonate with OTE (0.51:0.84:0.84) with enhanced thermal stability. A Si anode cycled in the new electrolyte exhibits a much thinner solid electrolyte interphase and a well-preserved dense structure. The electrolyte design principle developed in this work can be used to extend the cycle life of other high-capacity electrode materials with large volume changes.