Here we present a new class of solid materials formed from a rigid-rod polyanion and an ionic liquid. This “molecular ionic composite” (MIC) behaves mechanically as a solid, but contains ions that move nearly as in a neat liquid. Specifically, prototypical MICs are based on solutions of the rigid-rod polyelectrolyte poly(2,2’-disulfonyl-4,4’-benzideneterephthalamide) (PBDT) combined with a range of ionic liquids (ILs), with the IL comprising 75-97% of the final solid. This composite exhibits an unprecedented combination of properties: ionic conductivity up to 8 mS/cm, tunable elastic modulus from 0.03-3 GPa, and thermal stability up to 300 deg. C. By varying the PBDT concentration in an aqueous seed solution as well as the type of IL and volume ratio of IL to the seed solution, we can widely tune MIC properties along with the kinetics of composite formation. These composite systems show promise as candidates for replacing flammable and volatile liquid electrolytes in rechargeable batteries especially when loaded with, e.g., lithium or sodium salts. When loading MICs with 4 M lithium, the composite forms a locally ordered polymer-IL matrix with a mixture of nano-scale crystalline structures. This electrolyte has shown long-term cycling in a Li-Li symmetric cell, thus demonstrating its promise for use in Li batteries.

Tunable and stiff solid electrolyte made from an ionic liquid and a rigid-rod polyanion

255th National Meeting (2018)

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