Thermal, mechanical, and electrochemical stability enhancement of Al2O3 coated polypropylene/polyethylene/polypropylene separator via poly(vinylidene fluoride)-poly(ethoxylated pentaerythritol tetraacrylate) semi-interpenetrating network binder

To overcome the thermal degradation and shrinkage of the commercial polyolefin-based separators in lithium ion battery, Al2O3 particles were coated on separators with a new binder. As the commonly used poly(vinylidene fluoride) (PVdF) binder has some drawbacks associated with the weak cohesive binding strength to both separator and ceramic particles, a new semi-interpenetrating polymer network (SIPN) type binder was synthesized by cross-linking ethoxylated pentaerythritol tetraacrylate (EPETA) in the presence of PVdF in this study. The Al2O3 coated polypropylene/polyethylene/polypropylene (PP/PE/PP) multilayer separator using this SIPN binder showed much higher thermal and mechanical stability than that using the pristine PVdF binder due to the enhanced adhesive strength of polar EPETA component. This polar nature of cross-linked poly(EPETA) also resulted in higher wetting and uptake of electrolyte liquid and lithium ion (Li+) conductivity, leading to enhanced electrochemical performance at high discharge rate.