Ion conductive polymer electrolyte membranes based on star-branched poly(ethylene-glycol tri-acrylate) and polysulfide macromonomers

This article presents star-branched polymeric co-networks consisting of a three-arm poly(ethylene glycol) acrylate macromonomers (PEG3A) and a three-arm polysulfide (PS) via UV photopolymerization for the development of ion conductive polymer electrolyte membrane (PEM) containing succinonitrile (SCN) plasticizer and lithium bis(trifluoromethane sulfonyl)imide (LITFSI) salt. The hyperbranched co-network (PS-co-PEG3A) exhibits a lower glass transition temperature (Tg = −49 °C at 50:50) relative to that of 3-arm (PEG3A), i.e., Tg of −32 °C, showing systematic variation with polysulfide addition. In the tensile tests, elongation-at-break of PEM – PS-co-PEG3A is higher, but it occurs at the expense of lower tensile strength and modulus. Moreover, PEM – PEG3A exhibits higher strength and modulus relative to those of PEM – PS-co-PEG3A copolymer, but its ionic conductivity is lower (i.e., 3.41 × 10−4 S/cm for PEM – PEG3A versus 1.35 × 10−3 S/cm for PEM – PS-co-PEG3A at 21 °C). This improved ionic conductivity may be attributed to reduced crosslinking density associated with the formation of SC bonds upon addition of polysulfide. The PEM – PS-co-PEG3A co-network is thermally stable up to 130 °C tested and exhibited reasonably good anodic stabilities up to 4.5 V versus Li/Li+. In the CV tests in half-cells configuration with LiFePO4 cathode against Li/Li+, the specific discharge capacity was found to be 120 mAh/g with capacity retention of about 97% for 50 cycles tested.