A gel polymer electrolyte membrane of polyhedral oligomeric silsesquioxane cross-linked poly(vinylidene fluoride-hexafluoropropylene) for lithium-ion battery

Separator of lithium-ion battery (LIB) faces safety challenges such as unsatisfied mechanical strength and insufficient dimensional stability especially at relatively high temperature. For that, a thermally stable nanoparticle of octavinyl polyhedral oligomeric silsesquioxane (OV-POSS) was mixed with poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) in solution in this work. It was found that the PVDF-HFP chains could be chemically linked with OV-POSS in the presence of ammonia water. The formed stable suspension of micelle was then cast to prepare a porous membrane. The dimensional stability, the mechanical properties and the microstructures of the obtained membranes were measured and analyzed, and compared with those of the membrane prepared by physically blending PVDF-HFP with OV-POSS. The results indicate that the chemically included OV-POSS nanoparticles can function as active filler to crosslink the PVDF-HFP chains, thus markedly reinforcing the membrane to improve its dimensional stability, but suppressing the crystallization of the polymer. The electrolyte up-taken membrane exhibits 0.76 mS∙cm−1 ionic conductivity, reveals 5 V electrochemical stable window and displays 0.75 lithium ion transference number, demonstrating an excellent gel polymer electrolyte (GPE). In addition, the GPE possesses higher rate ability and better cycle performances according to the battery tests. Therefore, our work provides a novel and easy strategy of cross-linking vinylidene fluoride polymer with reactive POSS to fabricate GPE with enhanced mechanical strengths, improved dimensional stability and better electrochemical properties, which suggests its promising potential in LIB.