A Method of Impedance Spectroscopy for Predicting the Dynamic Behavior of Electrochemical System and Its Application to a High‐Area Carbon Electrode

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Abstract
A method for calculating the time‐domain response to a periodic signal imposed on a system from impedance spectroscopic data is described. Since impedance is one of the system functions, a current (or voltage) response to voltage (or current) signal imposed on a system can be calculated from the impedance spectrum by performing a Fourier transform of voltage or current signals combined with an operational form of Ohm's law in the frequency domain. To show the applicability of the method to an electrochemical system, a high‐area carbon electrode in a nonaqueous electrolyte was selected. A large capacitance characteristic of high‐area carbons, 0.52 F per 3 cm2 of apparent electrode area (140 F per gram based on the carbon sample weight), appeared in the low‐frequency region below 1 mHz, while a small capacitance of 25 μF per 3 cm2 (a typical value for a double layer) was observed for higher frequencies than 100 Hz. In a midfrequency range of 10−1 to 101 Hz, the electrode behaved like a resistor. Cyclic voltammograms at various sweep rates were calculated from the impedance spectrum. A one‐to‐one correspondence between calculated and directly measured voltammograms was obtained, and a characteristic feature of a high‐area carbon electrode is described. The feasibility of applying the proposed method to materials research for advanced batteries, including supercapacitors, is discussed.

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