A facile one-pot synthesis of solid polymer electrolytes (SPEs), composed of carbonate terminated poly(ethylene glycol) (CH3O-PEG-IC), poly(ethylene glycol)-block-polystyrene (PEG-b-PS) block copolymer nanoparticles containing a conductive PEG corona, fumed SiO2 and LiTFSI salt via polymerization-induced self-assembly is proposed. This method to prepare SPEs has the advantages of one-pot convenient synthesis, avoiding use of organic solvent and conveniently adding inorganic additives. CH3O-PEG-IC combines advantages of PEG and polycarbonate, the in situ synthesized PEG-b-PS nanoparticles containing a rigid polystyrene (PS) core and a PEG corona guarantee continuous lithium ion transport in the synthesized SPEs, and the fumed SiO2 optimizes the interfacial properties and improves the electrochemical stability, all of which afford SPEs a well considerable room temperature ionic conductivity of 1.73 × 10−4 S/cm, high lithium transference number of 0.53, and wide electrochemical stability window of 5.5 V (vs. Li+/Li). By employing these SPEs, the assembled solid state cells of LiFePO4|SPEs|Li exhibit considerable cell performance.