A semiconductor physics based model for thermal characteristics in electronic electrolytic energy storage devices

Abstract

A model for ultracapacitor capacitance and ion screening length based on semiconductor physics is presented in this paper. Screening length is related to capacitance as the plate-plate separation in a double-layer, and thus both are related to dissolved ion density in the electrolyte. Furthermore, this dissolved ion density can be expressed in terms of an effective bandgap assigned to the electrolyte/solvent pair. Therefore, by knowing the effective bandgap, we can explain the published experimental measurements of the dependence of capacitance and screening length on temperature. For electrolytes commonly used in ultracapacitor applications, the effective bandgap is estimated to be on the order of a few 100 meV.