High Conductivity Solvates with Unsymmetrical Glymes as New Electrolytes

A designed custom glyme ether with unsymmetrical (ethyl and butyl) end groups (UG) has been shown to give highly conducting liquid solvate electrolytes. Solvates prepared with UG glyme: salt ratios of 1:1, 2:1, and 3:1 using lithium bis­(trifluoromethane sulfonyl) imide (LiTFSI) and lithium bis­(fluoro sulfonyl) imide (LiFSI) lithium salts have been characterized with emphasis on the 2:1 composition. Conductivity in the order of 10–3 S/cm was observed at room temperature with an electrochemical stability window of 4.5 V. DSC studies indicate a low crystallization temperature between −60 °C and −75 °C for LiFSI based solvate electrolyte. Galvanostatic cycling studies (C/10) with LiFePO4 electrodes indicate a capacity deliverance of 145 mAh/g and good C-rate capability up to 2C at room temperature. Preliminary tests using unsymmetrical glyme-based solvate electrolytes with sulfur and LiNi1/3Mn1/3Co1/3O2 (NMC) electrodes reveal a low degree of polysulfide dissolution with sulfur electrodes and stable voltage profiles with NMC electrodes suggesting the use of these electrolytes for Li/S batteries and high-voltage Li-ion batteries.