Solid polymer electrolytes have the potential to enable safer and more energy dense batteries; however, a deeper understanding of their ion conduction mechanisms, and how they can be optimized by rational molecular design, is needed to realize this goal. Here, we investigate the impact of anion dissociation energy on ion conduction in solid polymer electrolytes via a novel class of ionenes prepared using acyclic diene metathesis polymerization of highly dissociative, liquid crystalline fluorinated aryl sulfonimide-tagged ("FAST”) anion monomers. These polyanions with various cations (Li+, Na+, K+, and Cs+) form well-ordered lamellae that are thermally stable up to 180 °C and feature domain spacings that correlate with cation size, providing channels lined with dissociative FAST anions. Electrochemical impedance spectroscopy (EIS) and differential scanning calorimetry (DSC) experiments, along with nudged elastic band (NEB) calculations, suggest that cation motion in these materials operates via an ion hopping mechanism. Moreover, the activation energy for Li+ conduction is 59 kJ/mol, which is amongst the lowest for systems that are proposed to operate via an ion conduction mechanism that is decoupled from polymer segmental motion. Furthermore, the addition of a 1 equivalent of a cation-coordinating solvent to these materials led to a >1000-fold increase in ionic conductivity without detectable disruption of the lamellar structure, suggesting selective solvation of the lamellar ion channels. This work demonstrates a novel molecular design strategy to facilitate controlled formation of dissociative anionic channels, which translates to significant enhancements in ion conduction in solid polymer electrolytes.
Synthetic methods, experimental and computational details, spectral data, supplemental references