Polymer-Ion Interaction Strength and Conductivity in Polymer Electrolytes

While polymer electrolytes hold the promise of improving safety and mechanical durability of electrochemical devices, most suffer from relatively low ionic conductivities especially at ambient temperature. This combination of challenges becomes even more pronounced in the conduction of the multivalent metal ions likely to be necessary for next generation, high energy density energy storage devices where the ions are likely to have complex, multi-functional interactions with the polyelectrolyte matrix. Metal-ligand coordinating polymers utilize labile bonds between polymer-bound ligands and free cations to delocalize and conduct mono- and multi-valent metal ions in the solid state. We have shown that the metal-ligand bonds also act as reversible cross-links, leading to delayed terminal relaxation in oscillatory rheology and universal behavior where conduction is related strongly to bond lifetime. Interestingly, these metal-ligand interactions appear to facilitate salt dissociation so the dielectric constant of the polymer backbone is less important than the ligand design.