Tunable Solid Electrolytes Formed from a Double Helix Polyanion and a Dense Sea of Mobile Ions

Recently our group discovered a new class of solid electrolyte materials, formed from a rigid-rod polyanion and an ionic liquid. This material’s cohesion arises from a massively collective electrostatic network, in which each polymer rod connects to its neighbors via the superposition of thousands of weak ion-ion interactions. The high degree of correlation of electrostatic interactions provide a stiff matrix, while individual ions move as if they were in a liquid. Thus, this material relieves the usual strict tradeoff between ionic conductivity and modulus in organic electrolytes, demonstrating its potential to resolve limitations in battery technologies, as well as in other molecular separations applications. We will discuss our fundamental understanding of the double helical supramolecular structure for the sulfonated aramid polymer that forms the reinforcing fibers (of aspect ratio ~1000) in this “molecular ionic composite” (MIC). We will also discuss the next larger level of hierarchical structure, the electrostatic network, and new ideas and new data on even larger morphological heterogeneities. Finally, we will present progress on incorporating 0.5 to 4 M of Li⁺ or Na⁺ and testing these MICs in electrochemical cells.