Preparation and Characterization of Electrospinning Crosslinked Gel Polymer Electrolytes

Gel polymer electrolytes (GPEs) for lithium ion batteries (LIBs) have attracted great attention due to their high ionic conductivity and safety, but it is still a great challenge to develop GPEs which can be used at high temperature in specific applications, such as oil drilling, mining, military and aerospace electronics. Cross-linking is one of the efficient methods for enhancing the thermal stabilities of GPEs. In this work, crosslinked gel polymer electrolytes (e-CGPEs) were made by electrospinning and Friedel-Crafts alkylation reaction. First of all, electrospun polymer membranes (e-PMs) were prepared by electrospinning technique with poly(vinylidene fluoride) (PVDF) as the matrix and polystyrene-b-poly(ethylene oxide)-b-polystyrene (PS-PEO-PS) triblock copolymer as the additive. Then the styrene units in e-PMs were crosslinked by Friedel-Crafts alkylation reaction to give electrospun crosslinked polymer membranes (e-CPMs). e-CPMs were activated by absorbing electrolytes to give crosslinked gel polymer electrolytes (e-CGPEs). The effects of PS-PEO-PS content (3%, 5%, 10%, 20%) on the properties of e-CPMs and e-CGPEs were also discussed. The results show that the content of PS-PEO-PS can affect the crystallinity, electrolyte uptake and crosslinked degree of e-CPMs, which may have influences on the ionic conductivity. Owing to the abundant crosslinked networks, high-temperature dimensional stabilities of eCPMs are much better than that of electrospun PVDF membrane and commercial polypropylene (PP) membrane. All e-CPMs show almost no dimensional shrinkage at 160 degrees C, indicating that e-CPMs can be efficient precursors of GPEs used at high temperature. e-CGPEs have better electrochemical performances than the PVDF-based GPE (e-PVDF), due to their high porosity, electrolyte uptake and ionic conductivity. Among all the e-CGPEs, e-CGPE 5% with proper PS-PEO-PS content and crosslinked degree possesses the highest ionic conductivity of 6.52 mS/cm at room temperature. The half-cell assembled by e-CGPE 5% shows a discharge specific capacity of 83.5 mAh/g at 2 C. e-CGPEs also exhibit excellent cycle and rate performances. e-CGPE 5% has a capacity retention of 99.7% after 100 cycles at 0.1 C. All the results suggest that e-CGPEs have potential application value in high-efficiency lithium ion batteries which could be used at high temperature. And this work also provides a new path for the preparation of crosslinked gel polymer electrolytes with high efficiency and good performance.