A universal equivalent circuit for carbon-based supercapacitors

Abstract

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.

Nitrogen doped superporous carbon prepared by a mild method. Enhancement of supercapacitor performance

“…The resistance of the cell can also be obtained from the X-axis intercept of the straight line observed at low frequencies of the diagram (the region where capacitive behavior of the capacitors is observed [26]) for all cases. The cell resistance is contributed by the resistance of charge transfer through the carbon particles and grainboundaries at the electrode-electrolyte surface (represented by a larger diameter of the semicircle with increasing the resistance [27]) and by diffusive problems of ions within the pore system (indicated by the appearance of a 45º impedance line, also known as the Warburg region, after the end of the semicircle and prior to the formation of the vertical line characteristic of capacitive behavior [25]). As can be seen, KUA-CONH2 Table 1) this difference cannot be explained by diffusional problems along the porosity.…”

All-solid-state micro-supercapacitors based on inkjet printed graphene electrodes

“…25 In particular, the CV curves are very stable. After 8 scan cycles, there is no visible voltage shift (except a small shift in the first cycle).…”

“…2(c) region, asynchronous charging region and non-charging region, which may reflect the presence of multiple pore sizes and/or types in the printed graphene electrodes. 25 In the lowfrequency (synchronous) region, the impedance plot exhibits an almost vertical straight line corresponding to ideal capacitive behavior. The synchronous region may result from the vertically oriented graphene flakes.…”

Supercapacitors: from the Leyden jar to electric busses

“…In a typical case of MnO 2 -based materials [62], the observed fading ranges from 5 to 30 % within thousand cycles depending on current load and binder content. At low binder content and at high current, the transmission resistance (a transmission line model not providing double-layer capacitance information was used as equivalent circuit [63]) deduced from impedance measurements increased indicating growing Ohmic contact resistance between the particles of the redox-active material and the carbon added for improved electric conductance. This was attributed to morphological changes induced by the volume expansion/contraction associated with the redox processes causing mechanical degradation of the electrode.…”