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

Tetrasiloxane and trisiloxane compounds were attached to oligo(ethylene oxide) chains, -(CH 2 CH 2 O)- n ( n = 2−7), via hydrosilation and dehydrocoupling reactions. The compounds were purified by solvent extraction and distillation before being characterized by 1 H, 13 C, and 29 Si 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.