Thermal, electrical, and mechanical properties of composite polymer electrolytes based on cross-linked poly(ethylene oxide-co-propylene oxide) and ceramic filler

A fully amorphous cross-linked poly(ethylene oxide-co-propylene oxide) (poly(EO/PO)) polymer electrolyte was prepared by chemical cross-linking reaction of a macro-monomer, poly(ethylene oxide-co-propylene oxide) with trifunctional cross-linkable acryloyl groups at the macro-monomer chain end. The lithium salt LiN(CF3SO2)2 ([Li]/[O]=1/16) and ceramic fillers such as BaTiO3 and γ-LiAlO2 adopted in the polymer electrolyte could maintain the fully amorphous feature of the polymer matrix. The submicron and nano-sized BaTiO3 fillers slightly decreased the thermal decomposition temperature of the polymer matrix, while the nano-sized γ-LiAlO2 filler improved to some extent the thermal stability of the polymer matrix. Both nano-sized BaTiO3 and γ-LiAlO2 fillers increased the ionic conductivity of the cross-linked poly(EO/PO)/LiN(CF3SO2)2 electrolyte and the highest conductivities of 5.67×10−5 S/cm at 30 °C and 5.76×10−4 S/cm at 80 °C, respectively, were obtained for the composite polymer electrolytes with 10 wt.% γ-LiAlO2 filler. However, the submicron BaTiO3 filler, regardless of its content, decreased the ionic conductivity. Addition of ceramic fillers, especially the nano-sized BaTiO3 and γ-LiAlO2, was effective in improving the mechanical strength and elasticity of the fully amorphous composite polymer electrolytes over a wide temperature range.