In Situ Cross-Linked Gel Polymer Electrolyte Membranes with Excellent Thermal Stability for Lithium Ion Batteries

Novel gel polymer electrolyte membranes with excellent thermal stability are fabricated via a combination of physical blending and chemical cross-linking procedures. Precursor porous membranes made of poly­(vinylidene fluoride) (PVDF) and polystyrene–poly­(ethylene oxide)–polystyrene (PS–PEO–PS) triblock copolymer composites are prepared by a phase-inversion technique, and the gel polymer electrolyte membranes are finished by in situ hypercrosslinking of the PS segments in precursor membranes. The latter cross-linking procedure could consolidate pore configuration and thus greatly enhance the thermal stability of the obtained cross-linked composite membranes. The membranes with optimal PS/PEO ratios can retain reasonable porosity with little dimensional shrinkage at high temperatures up to 260 °C. Gel polymer electrolytes with these cross-linked membranes as matrices exhibit much higher ionic conductivities (up to 1.38 × 10–3 S cm–1 at room temperature) than those based on pure PVDF membranes. Li/LiFePO4 half cells assembled with these gel polymer electrolytes exhibit good cycling performance and rate capability. These results indicate that the Friedel–Crafts reaction based hypercrosslinking is an efficient method to construct highly heat-resistant polymer electrolytes for lithium ion batteries, particularly advantageous in applications that require high-temperature usage