Design of polymer electrolytes to realize high lithium-ionic conductivity with fast interfacial charge transfer

Abstract

To achieve high lithium-ionic conductivity in polyethers together with fast charge transfer reaction at the polymer electrolyte/electrode interface, novel polymer electrolytes based on hyper-branched polyether matrices have been prepared. The polymer electrolytes exhibited a high ionic conductivity of the order of 10-4 S cm-1 at room temperature due to synchronization of the ionic transport with the fast molecular motion of the short and flexible ether side chains. By introducing trivalent boric acid esters in the polyethers and by alloying the polyethers with lithium salts of perfluorinated polyimides, polymer electrolytes having both high lithium-ionic transference number and high conductivity were obtained. The introduction of the free ether side chains into polyether matrices also contributed to decreases in the interfacial charge-transfer resistance at the metallic lithium anode and at the LiCoO2 cathode. A lithium salt of a weakly coordinating anion having low Tg, incorporated in the hyper-branched polyether matrices, afforded both high ionic conductivity and low charge-transfer resistance. Based on these results, lithium ionic liquids were designed and incorporated into the polyethers. The ionic conductivities of the polymer electrolytes were higher than those of the ionic liquids themselves. The combination of lithium ionic liquids and hyper-branched polyether matrices would be a novel strategy to realize low resistance in polymer electrolytes and at the solid-solid interface between polymer electrolytes and electrodes.