<p>Solid polymer electrolytes (SPEs) are flexible and exhibit wide application prospects. However, their low ionic conductivity at room temperature largely restricts their practical use in next-generation solid-state lithium batteries. A composite polymer electrolyte (CPE) that combines the advantages of soft chains and rigid particles is constructed to balance the electrochemical properties and mechanical strength. Hydrophobic nano-fumed silica (SiO₂) fillers are uniformly distributed in the dense cross-linking -CH₂-CH₂O- network, which is composed of polyethylene oxide and tetraglyme that is triggered by ultraviolet irradiation. The increasing amorphous region of the resulting CPE, due to the cross-linking and nanoparticles doping, facilitates an excellent electrochemical property with an ionic conductivity of 0.29 mS·cm^− 1 and a lithium transference number of 0.60 at room temperature. Moreover, the compact film with a tensile elongation of 57% can provide close interfacial contact and ensure more security for cells at work. The assembled Li||LiFePO₄ cells can deliver a reversible specific capacity of 160 mAh g^− 1 at 0.1&#xa0;C at room temperature and a capacity retention of 98% after 100 cycles. This study proposes a novel method for creating high-performance composite solid electrolytes at room temperature.</p>