Characteristics of gel electrolytes formed by self-aggregating comb-shaped polyethers with end-functionalised side chains

Gel electrolytes based on comb-shaped polyethers have been prepared and characterised. The comb-shaped polyethers consisted of poly(ethylene oxide) (PEO) or poly(ethylene oxide-co-propylene oxide) (PEOPO) side chains tethered to styrenic backbone polymers. All the polyether side chains were terminated by hydrocarbon (C16) chain ends. Polymer gel electrolytes were prepared by adding 10–70 wt.% of an electrolyte solution with 1 M lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) salt in γ-butyrolactone (γ-BL) or in a mixture of ethylene carbonate and diethyl carbonate (EC/DEC). Thermal analysis by differential scanning calorimetry (DSC) showed endotherms arising from the melting of hydrocarbon phase domains, indicating polymer self-aggregation in the gels by microphase separation of the chain ends. As the concentration of electrolyte solution was increased, the melt temperature of the hydrocarbon phase domains was found to decrease, while the heat of fusion in joules per gram polyether remained essentially constant. The latter finding implied a strong propensity for the hydrocarbon chains to phase separate in the electrolytes. This was further supported by small-angle X-ray scattering measurements which showed a characteristic diffraction distance of approximately 60 Å in the gels. The ion conductivity of the electrolytes with 70 wt.% of electrolyte solution added typically reached 10−2.5 S/cm at 20 °C.