This work has investigated that the electrochemical properties of PEO–lithium bis(perfluoroethylsulfonyl)imide (LiBETI)–SiO2 with different surface groups. The ac impedance, cyclic voltammetry, scanning electron microscope (SEM), X-ray diffraction (XRD) were used for understanding electrochemical characteristics of prepared composite electrolytes. Composite electrolytes prepared with SiO2 covered with trimethylsilyl exhibited good electrochemical properties. The ionic conductivity of composite polymer electrolytes (CPE) reached a maximum of about 1.5×10−5 S/cm at 25°C. This result was obtained since SiO2 covered with trimethylsilyl is suitable for increasing dispersability as well as not impeding the role of the SiO2 surface.