Mixed-Polarity Copolymers Based on Ethylene Oxide and Cyclic Carbonate: Insights into Li-Ion Solvation and Conductivity

Abstract

This study investigates the relationship between polarity and ionic conductivity in random and block copolymer electrolytes comprising highly flexible oligo(ethylene oxide) methyl ether methacrylate (OEM) and highly polar but glassy glycerol carbonate methacrylate (GCMA) monomers, blended with either lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium triflate. Interestingly, the high polarity of GCMA did not significantly enhance ionic dissociation, and the random copolymers (POEM-r-PGCMA) showed similar or lower ionic conductivities than the POEM homopolymer. Further analysis revealed that Li+ only interacts with OEM and its counterion, not with GCMA. The less-intermixed and weakly phase-separated block copolymer (POEM-b-PGCMA) exhibited even lower conductivities than the random copolymer. Our results suggest that Li+ solvation occurs only in the POEM-rich phase and that the larger PGCMA regions, depleted of Li+, disrupt long-range ion transport. These findings provide valuable insights into the design of polymer electrolytes and how segmental mobility and functional groups with contrasting polarities affect ion transport.