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.

Entropic Penalty Switches Li+ Solvation Site Formation and Transport Mechanisms in Mixed Polarity Copolymer Electrolytes

“…The corresponding connectivity κ is (3.94 ± 0.89) × 10 –4 in PGCMA- r -POEM, half of that of POEM (7.85 ± 1.15) × 10 –4 . This ratio is consistent with the reported two-fold difference in conductivity observed in experiments …”

“…Experimentally, the addition of 40 wt % PGCMA was reported to raise the T g by ca. 50 K . Consistent with experiments, the simulated T f is increased by 37 K after 50 wt % PGCMA is incorporated into the mixed system.…”

“…Studies of Li + transport in mixed polymeric materials have been limited, and a mechanistic understanding of the underlying molecular processes is still lacking. Past reports of mixed SPE materials have typically involved a high- T g , nonconducting polymer mixed with a rubbery ion-conducting polymer to improve the mechanical strength. − ,, In those systems, the nonconducting components are found to not only slow down the segmental dynamics of the conducting component ,, but also disrupt the conducting network. ,,, As the degree of miscibility increases, interconnected solvation sites tend to disintegrate into clusters. As a result, long-range Li + in those blends is often found to involve two time scales, one associated with local Li + hopping within a cluster and another associated with transport between clusters upon network rearrangements …”

“…In this work, we build on the hypothesis that a suitable contrast of mobility and polarity in SPE systems is best achieved when the low- T g , conductive PEO-based polymer is selected as the DMC analogue and a polymer containing highly polar cyclic carbonate groups is selected as the EC analog. In recent experiments from our group, the POEM/poly­(glycerol carbonate methacrylate) (PGCMA) pair was shown to provide a desirable contrast of polarity and mobility . Perhaps counterintuitively, experiments indicate that in LiTFSI-doped PGCMA- r -POEM, the highly polar cyclic carbonate interacts with the Li ions only minimally and the polyether segments are responsible for Li + solvation.…”

In Situ Formed Poly(ester-alt-acetal) Electrolytes with High Oxidation Potential and Electrode–Electrolyte Interface Stability

“…As shown in Figure c and Table S1, the samples with 5, 15, 30, 50, and 70 wt % lithium salts have the calculated [CO···Li + ]/[total ester group] ratio ( f CO···Li + ) of 22, 15, 25, 30, and 45 mol %, respectively. Because of the stronger affinity of the acetal group for Li + than the ester group, ,− with introducing more lithium salts, the coordination number of Li + with the acetal group is saturated first, and then excess Li + is coordinated with the ester group. The novel ester- alt -acetal structure has a variety of Li + coordination configurations and binding sites.…”