(15e) Solvation Against Polarity: A Simulation Study on Mixed-Polarity Grafted Polymer Electrolytes

Recent designs of solid polymer electrolytes for Li⁺ conduction consider the synergy between polarity and mobility contrast to achieve improved conductivity. To assess this idea, we employ MD simulations to compare Li⁺ solvation and transport behaviors in poly(oligo oxyethylene methacrylate) (POEM) versus in its copolymers with poly(glycerol carbonate methacrylate) (PGCMA). Unexpectedly, the highly polar PGCMA does not actively solvate Li⁺. Instead, the Li⁺-ether solvation is favored due to its relatively low entropic penalty. Further, we find that the presence of PGCMA promotes single-chain solvation and thereby suppresses inter-chain hopping. The findings suggest that the polarity contrast provided by PGCMA barely assists Li⁺ solvation or improves Li⁺ transport. Finally, compared to PGCMA-r-POEM, the less-mixed PGCMA-b-POEM shows decreased Li⁺ transport. The observed trend is explained by further analysis on solvation site network connectivity. The discussions on thermodynamic driving forces for ion solvation preferences and on effects of mixing on long-range Li⁺ transport are insightful for future mixed SPE designs.