Modulating Ion Transport and Self-Assembly of Polymer Electrolytes via End-Group Chemistry

We report a rational design of solid-state dry polymer electrolytes with high conductivity, high mechanical strength, and improved cation transference number. Thiol ene click chemistry provided orthogonal control over the type and number of end groups in poly(styrene-b-ethylene oxide) (PS-b-PEO) block copolymers. This approach permitted the synthesis of PEO chains with reduced crystallinity, reminiscent of PEO oligomers, thereby playing a key role in improving the room temperature conductivity. Intriguingly, the incorporation of diol or dicarboxylic acid end groups in PS-b-PEO produced a well-defined gyroid structure, leading to order of magnitude improvements in the storage modulus. Out of the various samples examined, the electrolytes bearing terminal diol displayed the highest ionic conductivity and a 2 -fold increase in lithium transference number. The improvements in performance are attributed to the reduced interchain aggregation and the anion stabilization mediated by the terminal diol group. The fact that the dramatic changes in ion transport and mechanical properties of PS-b-PEO samples were brought about solely by the modification of single terminal group of the PEO unit confirmed end-group chemistry as a powerful tool for the design of efficient solid-state polymer electrolytes. This work should find applications in various emerging electrochemical technologies, namely those employed in energy storage and conversion.