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A family of coefficients for quantitative assessment of hysteresis in cyclic voltammetric (CV) curves of electrochemical capacitors and of electrodes for electrochemical capacitors has been defined. Hysteresis index 1 (HI1) is based on the maximum in the difference in current measured at the same potential in ascending and descending branch of CV curve, and HI2 is based on the average difference in current measured at the same potential in ascending and descending branch of CV curve. The values of HI1 and HI2 range from 0 (no hysteresis) to 1 for an ideal capacitor. CV curves of two commercially available electrochemical capacitors over a potential range 0–1500 mV at scan rate of 5 mV/s showed HI1 of 0.94 and 0.97 and HI2 of 0.77 and 0.83, respectively. At the same experimental conditions, a series of 52 home made electrochemical capacitors showed HI1 up to 0.7 and HI2 up to 0.55. HI1 and HI2 measured at constant scan rate (5, 20 or 50 mV/s) in that series of capacitors showed a correlation coefficient >0.98 while HI1 and HI2 measured at different scan rates showed limited correlation. 98 CV curves of electrochemical capacitors and of electrodes for electrochemical capacitors from literature, obtained at various conditions show HI1 from 0.42 to 1, HI2 from 0.27 to 0.97, and a correlation coefficient of 0.90 between HI1 and HI2.
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