Poly(ethylene oxide) (PEO)-based composite electrolyte membranes, which silica (SiO2) and lithium bis(trifluoromethylsulf)imide (LiTFSI) were introduced into, were successfully prepared by a self-developed eccentric rotor mixer based on an elongational flow field. Characterization results of electrolyte membranes showed that the eccentric rotor mixer can realize the uniform dispersion of LiTFSI in all electrolyte membranes. This produced a high ionic conductivity of the electrolyte membrane. Among all as-prepared membranes, the ionic conductivity of PEO5 exhibited the highest value of 2.96 × 10–4 S·cm–1 at room temperature due to reaching an extremely uniform dispersion of SiO2. After 90 charge–discharge cycles, the Coulomb efficiency of the LPF/PEO5/Li was still close to 100%, and the discharge specific capacity weakly decreased, revealing an extremely good electrochemical performance of PEO5. Therefore, the eccentric rotor mixer provides an effective strategy for facilitating the development of high-efficiency all-solid-state lithium-ion batteries.