(506b) Understanding Ion Transport in Single-Ion, Bottlebrush Copolymer Electrolytes through Experiments and Simulations

Single-ion conducting polymer electrolytes (SICPEs) have emerged as a potential solution to electrolyte concentration gradient formation in lithium metal batteries. We investigate ion transport in bottlebrush SICPEs using a combination of experiments and atomistic simulations. A series of solvent-free SICPEs were synthesized by copolymerization of poly(ethylene glycol) methyl ether acrylate (PEGMEA) with varying lithiated anionic groups in different monomer ratios. Carboxylates, sulfonates, and trifluoromethanesulfonyl imides were incorporated into the polyanions in varying controlled compositions. The highest ionic conductivities were observed for the electrolytes prepared with PEGMEA and methacrylatepropyl(trifluoromethanesulfonyl) imide (MPTFSI) monomers (~ 10^–5 S/cm at 30 ºC), but a counterintuitive negative correlation between conductivity and ion composition emerged. Our simulation results suggested that the Li⁺ diffusion was correlated to the polymer mobility for electrolytes with low compositions of anionic groups in the copolymer. In agreement with experimental findings, an improved decoupling of ionic conductivity from polymer dynamics was observed at high anion composition. In this regime, the primary mechanism of Li⁺ transport was by successive hopping within the percolated ionic aggregates. This mechanism required a higher activation energy that limited ionic conductivity at low temperatures. Finally, we examined ion-aggregate morphology in simulation and through small angle X-ray scattering to demonstrate the counterintuitive influence of anion chemistry on ionic conductivity in solvent-free SICPEs. This study suggests that future bottlebrush SICPEs should aim for high anion content and consider aggregation morphology to promote high single-ion conductivity.