A universal equivalent circuit for carbon-based supercapacitors

A universal equivalent circuit is proposed for carbon-based supercapacitors. The circuit, which actually applies to all porous electrodes having non-branching pores, consists of a single vertical ladder network in series with an RC parallel network. This elegant arrangement explains the three most important shortcomings of present-day supercapacitors, namely open circuit voltage decay, capacitance loss at high frequency, and voltammetric distortion at high scan rate. It also explains the shape of the complex plane impedance plots of commercial devices and reveals why the equivalent series capacitance increases with temperature. Finally, the construction of a solid-state supercapacitor simulator is described. This device is based on a truncated version of the universal equivalent circuit, and it allows experimenters to explore the responses of different supercapacitor designs without having to modify real supercapacitors.