Complex capacitance analysis of porous carbon electrodes for electric double-layer capacitors

A new analytical methodology, complex capacitance analysis, is developed for porous carbons that are employed as electric double-layer capacitor (EDLC) electrodes. Based on the transmission line model, the imaginary capacitance profiles (C-im vs. log f) are theoretically derived for a cylindrical pore and further extended to multiple pore systems. The theoretical derivation illustrates that two important electrochemical parameters in EDLCs can be estimated from the peak-shaped imaginary capacitance plots: total capacitance from the peak area and rate capability from the peak position. The usefulness of this analysis in estimating EDLC parameters is demonstrated by applying to two sets of practical porous carbon electrodes. In addition, the penetrability distribution curves that are derived from the experimental imaginary capacitance data using the log-normal assumption and discrete Fourier transform allow us to estimate the pore structure of carbon electrodes. (C) 2004 The Electrochemical Society.