High-Voltage-Compatible\nDual-Ether Electrolyte for\nLithium Metal Batteries

Abstract

To improve the energy density of\nrechargeable batteries, lithium\nmetal batteries (LMBs) consisting of high-voltage cathodes and metallic\nlithium anodes have been actively studied. Ether-based organic electrolytes,\nparticularly 1,2-dimethoxyethane (DME), show good performance for\nLMB anodes, but due to low oxidation stability, they are difficult\nto apply in conjunction with high-reaction-voltage cathodes such as\nlithium cobalt oxide (LCO). Here, a dual-solvent system with fluorinated\nether with high oxidative stability added as a co-solvent is used\nto increase the electrolyte oxidation stability. It is found that\ntetrafluoroethyl tetrafluoropropyl ether (TTE) is most suitable for\nuse as the co-solvent, due to its non-solvation of Li salts and miscibility\nwith DME arising from its non-polar nature. Introduction of a DME/TTE\ndual solvent with 1.0 M lithium bis­(fluorosulfonyl)­imide (LiFSI) increases\nthe concentration of the salt coordinated by DME to an ultra-high\nelectrolyte concentration of 5.0 M LiFSI. The oxidation stability\nof the electrolyte is improved by increasing the amount of the DME–Li⁺ complex. The DME/TTE ratio and the Li salt concentration\nof the dual-ether electrolyte are optimized through physical and electrochemical\nanalyses. Compared to the conventional carbonated electrolyte, the\ndual-ether electrolyte shows low resistance and improved cycle performance\nin LMBs with an LCO cathode.