A Study on the Effects of Porous Structures of Polymer Matrixes on the Properties of Gel Polymer Electrolytes for Lithium Ion Batteries

Lithium-ion batteries (LIBs) share a large fraction of the secondary battery market. Continuous efforts are made to address some critical issues required for current LIBs, such as safety, high charging rate, and long-term cycling stability. In this work, poly(vinylidene difluoride) porous membranes with different porous structures, prepared from nonsolvent-induced phase separation (NIPS) and vapor-induced phase separation (VIPS) processes, are employed as the polymer matrix for gel polymer electrolytes (GPEs). The effects of porous structures of polymer matrices on the properties of the corresponding GPEs are examined and discussed. The macrovoid pores of the NIPS membrane provide a high porosity and a high liquid electrolyte uptake, contributing to increasing the ionic conductivity of the corresponding GPE. Nevertheless, its dense top layer brings a restricted effect on ionic flow. The NIPS membrane-based GPE exhibits less stability in continuous lithium plating/stripping tests. On the other hand, the VIPS membranes contain continuously interconnected pores, consequently bringing stable ionic flows and depression on lithium dendrite growths to the corresponding GPEs. The VIPS membrane possessing relatively small pore sizes is preferred. A summary of the designed porous membrane structure for GPEs could be an asymmetric porous membrane that possesses a top layer with continuous interconnected pores having small pore sizes and a bulk fraction with a macrovoid porous structure having a high porosity.