Capacitance Characterization Methods and Ageing Behaviour of Supercapacitors

Commercial MAXWELL capacitors were investigated by ac impedance spectroscopy, chronoampero- metry, constant current discharge and other transient techniques in order to determine rated capacitances reliably. Capacitance is outlined as a dynamic quantity that depends on the voltage and the state of charge of the supercapacitor. Capacitance is devided up in a double-layer capacitance at the "outer" electrode surface and a pseudocapacitance due to slow electrochemical processes depending on voltage: C = C0 + kU. Rated capacitance is determined as the differential capacitance at 50% or 75% of the rated voltage U0, advantageously.