Synthesis and Characterization of Tetra- and Trisiloxane-Containing Oligo(ethylene glycol)s Highly Conducting Electrolytes for Lithium Batteries

Abstract

Tetrasiloxane and trisiloxane compounds were attached to oligo(ethylene oxide) chains, -(CH2CH2O)-n (n = 2−7), via hydrosilation and dehydrocoupling reactions. The compounds were purified by solvent extraction and distillation before being characterized by 1H, 13C, and 29Si NMR. Upon being doped with lithium bis(oxalato)borate (LiBOB) or lithium bis(trifluorosulfonyl) imide (LiTFSI), the electrolytes showed ambient temperature conductivities ranging from 2 × 10-4 to 6 × 10-4 S cm-1. These low viscosity compounds have conductivities that are among the highest observed to date for liquid “polymer” electrolytes. Temperature-dependent conductivity studies suggest that the ethylene oxide chains contribute to ion transport as a polymer would. The amorphous behavior of the electrolytes was observed by differential scanning calorimetry, which revealed very low glass-transition temperatures before and after doping.