Correlating Mobile Ion Radius with Ion Transport Activation Energy in Single-Ion Conducting Polymers

Single-Ion Conducting Polymers (SICPs) are promising candidates for next-generation solid-state batteries as they offer a high transport number (t₊~1). However, SICPs typically suffer from low conductivity due to a high activation energy (E_a) for ion transport. The Arrhenius approach often yields large E_a values and unphysical pre-exponential factors (t₀). This approach assumes a temperature-independent E_a, which is not true for the polymer electrolytes. To address this methodological issue, our group recently introduced an alternative method that imposes a physically realistic ion hopping attempt time (t_{0 ~ 10}^-13 s). This new approach yields a significantly lower and temperature-dependent energy barrier (E*(T)), which varies even in the glassy state, suggesting a revised physical picture for ion hopping.

We used Broadband Dielectric Spectroscopy and Brillouin Light Scattering (BLS) to investigate the parameters controlling this E*(T). Our key finding is that the local coulombic interactions are the dominant factor governing the overall transport barrier across different mobile ion radii.<span style="font-size:10.8333px"> This holds true even for large ions, such as imidazolium, where the influence of polymer matrix elastic forces is surprisingly weak. These results provide vital, fundamental insights for a rational design of highly conductive SICPs.