Polymer networks are promising materials for replacing organic liquids as electrolytes as the modulus can be tuned independently of conductivity. When the crosslinks are dynamic bonds, they offer the additional benefits of recyclability and self-healing. Here we report a fundamental study on ion transport in dynamic network electrolytes (DNEs) comprised of precise linker lengths of 2, 3, or 4 repeat units of ethylene oxide. The oligomeric chains were first crosslinked with boric acid to form trifunctional boronic ester junctions. The DNEs’ conductivity was measured over a range of salt contents and temperatures to understand how linker length and anion-boron interactions affect ion transport. Added salt increases conductivity up to a point where aggregation occurs, while the modulus and viscosity decrease due to coordination with the boronic esters. With decreasing linker length, a monotonic decrease in conductivity is observed as the network begins to confine ion transport. Detailed analysis accounting for Tg and rheological measurements show that conductivity is decoupled from segmental dynamics for these materials and imply that dynamic bonds can play a crucial role in ion transport. Analogous networks were also prepared with vinylogous urethanes dynamic bonds which show much lower conductivity for a given crosslink density (and similar modulus). Solid-state NMR indicates coordination with the cation which impacts the conductivity and relaxation time. These results show the importance of bond selection in DNEs.

Effects of crosslink density, salt, and bond selection on conductivity and relaxation in dynamic network electrolytes

ACS Spring Meeting 2021

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