Synthesis and characterization of a novel physically cross-linked gel polymer electrolyte

A physically cross-linked gel polymer electrolyte (GPE) was obtained by photo-induced radical polymerization of a mixture of methoxy-poly(ethylene glycol) methacrylate (MPEGM), hexadecal-poly (ethylene glycol) methacrylate (HPEGM), triethylene glycol dimethyl ether (TEGDME), lithium salt (lithium perchlorate, LiClO₄), and photo-initiator (2,2-dimethoxy-2-phenylacetophenone, DMPA). The resulting polymers and gel polymer electrolytes were characterized by infrared spectroscopy (IR), differential scanning calorimetry (DSC), tensile test, and alternating current (AC) impedance measurements. The results showed that the physically cross-linked polymer matrix was formed by C₁₆ aggregation with the effect of electrostatic repulsion of PEO chains when the HPEGM content was high. The ionic conductivity of the obtained GPE is affected by its composition and the temperature. The GPE prepared with the optimum composition exhibited excellent mechanical properties and a relatively high ionic conductivity (up to 8.7× 10^-4 S·cm^-1 at 30 °C). In addition, the GPE was found to present a wide electrochemical window (from 0 to 4.5 V (vs Li/Li ⁺). In addition, a coin cell based on the gel electrolyte, with LiFePO₁₆/C as the cathode and metallic lithium as the anode, showed a discharge capacity as high as 154.7 and 148.0 mAh·g^-1 at 30 °C under 0.1C and 0.2C rates, respectively.