The decay of charge in a capacitor is similar to the decay of a radioactive nuclide. It is exponential decay. If we discharge a capacitor, we find that the charge decreases by half every fixed time interval - just like the radionuclides activity halves every half life.
The voltage, current, and charge all decay exponentially during the capacitor discharge. We can charge up the capacitor and then flip the switch and record the voltage and current readings at regular time intervals and plot the data, which gives us the exponential graphs below. The half life of the decay is independent of the starting voltage.
The capacitance of a supercapacitor can decrease if its aging leads to an outflow current shape change in a 1 mol L−1 Li2 SO4 electrolyte on a 2-hour detached time and at 1.6 V. This is shown in the growth of outflow current in 60 runs at 1.5 V and 1.6 V.
Since the development and production of electrolytic capacitors, designers have had to deal with the issues of aging and shelf life of these products. Electrolytic capacitors have been around for a very long time, but the rapid increase did not occur until the 1960s.
The supercapacitor is modelled by the circuit consisting of two ideal capacitors, two ideal resistors and one resistor with the time dependent resistance value. The capacitors C1 and C2 are representing the capacitance of Helmholtz double layer C H and the increase of capacitance due to the diffusion of charges in the electrolyte C D, respectively.
Aging laws of electrolytic capacitors. Many techniques deal with life forecast and failure detection of aluminum electrolytic capacitors which are utilized as a part of power electronic converters. The main idea of these techniques is to estimate the values of Equivalent Series Resistance (ESR) and Capacitance (C).