High-Modulus Single-Ion-Conducting Electrolytes Based on a Rigid-Rod Polyanion

Single-ion-conducting electrolytes enable easy processing and can block Li dendritic growth, showing potential for use in solid-state batteries. We report solid electrolytes that combine a rigid-rod polyanion, poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) (PBDT), with Na⁺ or Li⁺ counterions, and poly(ethylene glycol) (PEG, M_n = 400 g mol^-1). PBDT-PEG membranes show Young’s modulus from 90 to 2110 MPa that increases with the PBDT content and is >4× higher for Li-based vs Na-based electrolytes. We attribute this dramatically higher modulus in LiPBDT-PEG to poorer ion dissociation between Li⁺ and PBDT sulfonate groups and stronger interactions between LiPBDT and PEG. These membranes show an increase in ionic conductivity with increasing PEG concentration (0.1-7 μS cm^-1 at 30 °C), reaching 0.13 mS cm^-1 at 120 °C. These materials use highly rigid and charged PBDT double helices to “solidify” low-molecular-weight PEG into mechanically strong and highly single-ion-conductive solid polymer electrolytes with high thermal stability. Their combination of high cation conductivity and high modulus exceeds those of competing single-ion conductors at 30 °C.