This study reports the preparation of a composite polymer electrolyte for application in LiNi0.5Co0.2Mn0.3O2 lithium-polymer batteries. Poly(vinylidiene fluoride-hexafluoropropylene) (denoted as PVDF-HFP) was used as the polymer host and mesoporous modified-silica fillers (denoted as m-SBA15) used as the solid plasticizer were added into the polymer matrix. The characteristic properties of the composite polymer membranes were examined using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and an AC impedance method. The discharge capacities of LiNi0.5Co0.2Mn0.3O2 polymer batteries with a PE separator, pure PVDF-HFP polymer membrane, or a PVDF-HFP/10wt.%m-SBA15 composite at 0.1C were determined to be 155.5, 159.5, and 198.6mAh g−1, respectively. The LiNi0.5Co0.2Mn0.3O2 polymer battery containing the PVDF-HFP/10wt.%m-SBA15 composite achieved discharge capacities of 194, 170, 161, 150, 129, 115, and 87mAh g−1 at 0.1, 0.2, 0.5, 1, 3, 5, and 10C, respectively. The lithium-polymer battery demonstrated a high coulomb efficiency of ca. 99%. The PVDF-HFP/m-SBA15 composite membrane is a strong candidate for application in LiNi0.5Co0.2Mn0.3O2 lithium-polymer batteries.