CF_x/SiO₂ composites with different SiO₂ sources have been synthesized as cathode materials for primary lithium batteries. The effect of modification with different SiO₂ sources on the performance of CF_x has been investigated with FT-IR, X-ray diffraction (XRD), scanning electron microscopy (SEM), BET, X-ray photoelectron spectroscopy (XPS), and electrochemical measurements (galvanostatic discharge, EIS). Based on the FT-IR and XPS analyses, it is confirmed that semi-ionic C–F has existed in SiO₂ modified CF_x and the F/C has decreased which may be caused by the reaction between SiO₂ and CF₂. The BET illustrated that the surface area of SiO₂ modified CF_x was extremely larger than that of pristine CF_x. Furthermore, electrochemical measurements displayed an enhancement in the discharge capacity and plateau of the CF_x/SiO₂ composites, as well as an improvement in their power density and energy density. In particular the CF_x–mSiO₂ exhibits a discharge capacity of 587 mA h g⁻¹, with a plateau of 2.28 V at a current density of 5C, accompanied by a maximum power density of 9689 W kg⁻¹ and about three times higher energy density than that of pristine CF_x.