A novel polymer electrolyte based on triblock copolymer of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) with ionically active SiO2 inclusions has been designed. The electrolyte shows favorable features for ion migration such as low glass transition temperature and high concentration of amorphous phase. Combined with the effect of active SiO2, its ionic conductivity is about 8.0×10−5 Scm−1 at 30°C, which exceeds that for the PEO-based systems. As applying them to cells with LiFePO4-type cathodes, a capacity of about 147.0mAhg−1 is obtained at 60°C, which is retained by more than 90% after 40 charge/discharge cycles. Moreover, about 100mAhg−1 could still be delivered as temperature decreases to 30°C.