
Metrologyultracapacitor and supercapacitor measurement methodologyMeasurement methods
The following chart shows that the capacitance values strongl depend on the measurement methods. The caracteristic measurement time or the frequency give higher value for slow measurements. The high values of bias voltage give higher capacitance values.
IEC 62391 standard
Cyclic VoltammetryThe voltage is swept between a lower limit to an upper limit at a fixed voltage scan rate. The voltage scan rate (v) is calculated from the slope of the line. The current evolution is measured as a function of the voltage. The characteristics of the linear sweep voltammogram recorded depend on a number of factors including:
Voltammetry applied to Li batteryImpedance spectroscopySee also Supercapacitor frequency properties Potentiostatic mode: ΔE(ω) is the imposed ripple voltage amplitude superposed on the bias E_{0}, and ΔI(ω) is the measured current on a constant current I_{0}. Galvanostatic mode: in that case it is a small current ripple amplitude which is imposed on a constant current and a ripple voltage which is measured. The impedance Z(ω) est un nombre complexe qui peut être ecrit sous deux formes equivalentes : Z(ω) = Z(ω) e^{jΦ(ω)} or Z(ω) = Z_{r}(ω) + jZ_{j}(ω) with j = 1, Z is the impedance module, Φ the phase, Z_{r} the real part and Z_{j} the imaginary part. The relations between the 2 equations is given by: Z^{2} = Z^{2}_{r} + Z^{2}_{j} and Φ = tan^{1} Z_{j}/Z_{r} where Z_{r} = Z cos Φ and Z_{j} = Z sin Φ Constant current chargeSee also Supercapacitor time properties C charge: Time between t_{0} and t_{2} C discharge: Time between t_{4} and t_{6} ESR charge: Voltage drop between t_{2} and t_{3} @ U_{n} (2 s) EST discharge: Voltage recovery between t_{2} and t_{3} @ U_{min} (2 s) In t_{2} there is an instantaneous drop of the voltage due the interruption of the charging current. The product r_{s}i vanished with the cutrrent. Between t_{3} and t_{4} the charge redistribution and the selfdischarge contribute to the voltage drop. Between t_{7} and t_{0} the charge redistribution contributes to an increase of the voltage and the selfdischarge contribute to a voltage drop. Source: Garmanage: Roland Gallay
