Highly conductive trimethylsilyl oligo(ethylene oxide) electrolytes for energy storage applications

Abstract

Monomethyl ethers of oligoethylene glycols with different chain lengths were converted to trimethylsilyl derivatives by reacting with trimethylchlorosilane in the presence of triethylamine, or by directly refluxing with excess trimethylchlorosilane or hexamethyldisilazane. Similarly, two oligoethylene glycols were converted to bis(trimethylsilyl) derivatives. When doped with lithium bis(trifluoromethanesulfonyl)imide, these electrolytes have very high conductivity, generally >10⁻³ S cm⁻¹. A full cell performance test using one of these new electrolytes (1NM3) showed excellent cyclability at room temperature. Introducing a second trimethylsilyl group decreases the conductivity of trimethylsilylated compounds. The thermal properties, viscosities and dielectric constants of the compounds were measured, and the effect of those on the conductivity is reported. Cyclic voltammetry experiments show that the trimethylsilylated compound (1NM2) of diethylene glycol monomethyl ether has greater electrochemical stability than its germanium and carbon analogues.