(129f) Investigation on Tethered Anion Effects in Solid Polymer Electrolytes for Li-Ion Conduction

Solid polymer electrolytes (SPEs) have been proposed to reduce concentration gradients by immobilizing anions to the polymer matrix, which can help stabilize the electrodeposition process and extend battery lifetime. Unfortunately, single-ion conducting SPEs continue to suffer from poor conductivity due to being coupled with the segmental mobility and their poor ion pair dissociation. Our group investigated how different tethered anions affected the Li-ion conduction and polymer segmental mobility. Copolymers were synthesized using a common neutral monomer, poly(ethylene glycol) methyl ether methacrylate (PEGMA), with a series of different anionic monomers: styrene sulfonate, styrene phosphonate, styrene TFSI, and methacrylate TFSI. These monomers presented a series of anions of varying strength with the same styrene structure, sulfonate vs. phosphonate vs. TFSI, as well as exploring structural monomer changes for the same TFSI anion, styrene vs. methacrylate, that allows for systematic changing of polymer electrolyte properties. Each copolymer series was further expanded by changing the composition of neutral-to-anionic monomers. The increased ion exchange capacity of the phosphonate groups led to a high degree of ion aggregation that showed very low conductivities. Increasing the electron delocalization of the ions from sulfonate to TFSI greatly improved the conductivities and lowered activation energies, with methacrylate being slightly better than styrene. Implications of these results will be discussed for next-generation polymer electrolyte design.