Experimental study of temperature effect on ultracapacitor ageing

Reliability is the key issue concerning ultracapacitor applications. In several power applications ultracapacitors are charged and discharged at high current which causes ultracapacitors heating. This paper presents ultracapacitor ageing according to the temperature. To investigate this effect, a test bench of accelerated ageing of ultracapacitor is carried out. Experimental tests are realized at constant temperature when the ultracapacitors are polarized at the maximum voltage. To quantify the ultracapacitor ageing, the equivalent series resistance (ESR) and the equivalent capacitance (Cequi) are measured using Electrochemical Impedance Spectroscopy (EIS). The cause of this ageing is the degradation of the electrolyte and the activated carbon. The electrolyte decomposes during the oxydoreduction phenomena which creates by-products. This degradation leads to an increase of the Equivalent Series Resistance. These by-products deteriorate also the surface of the activated carbon which generates the reduction in the capacitance. After these tests, the ultracapacitor lifetime is obtained versus temperature for the fixed voltage. With the use of the law of Arrhenius the ultracapacitor lifetime is generalized at all the temperatures but always for an extreme voltage which is the nominal voltage of the component. Finally, other tests on various ultracapacitors are made to generalize the lifetime of the ultracapacitor according to the temperature.