Composite Electrolytes Prepared from Fumed Silica, Polyethylene Oxide Oligomers, and Lithium Salts

The conductivity of solution electrolytes containing lithium salts (imide and triflate anions), poly(ethylene glycol), and mono‐ and dimethyl‐terminated poly(ethylene glycol) (Mw 200 to 400), and their corresponding composite electrolytes containing fumed‐silica particulates (0 to 20 weight percent) are reported. At room temperature the ionic conductivity is as high as for the composites studied, and they exhibit a gel‐like consistency but flow under shear. The electrochemical stability of the composites and compatibility with lithium metal were also examined. A large potential window (∼5.5 V) was found for Li imide‐based electrolytes. The passive film formed on lithium in contact with the composite electrolyte is relatively more stable and less resistive than that formed in contact with the parent solution electrolyte. Considering the additional advantages of processability and low volatility, these composites should be good candidate electrolytes for lithium and lithium ion batteries.