Complex thermal analysis of supercapacitor by thermal impedance spectroscopy

Thermal impedance spectroscopy (TIS) measurement was developed for thermal analysis of supercapacitors. Compared with previously reported TIS measurement methods, the specific heat flux path through the supercapacitor device can be manipulated under the experimental system equipped with cold and heat sources. Using complex notation, the thermal impedance was defined as the ratio of the measured temperature difference across the tested device to the imposed heat flux. Different from the performance of Li-ion batteries, the thermal impedance spectra of the tested supercapacitor showed two semicircles with different diameters. The negative real part of the thermal impedance in the high frequency region could be considered as a frequencyrelated phase delay caused by the time response of the thermocouples in the temperature measurement. In addition, heat capacities and thermal resistances of the active materials and the casing of the tested supercapacitor were derived by equivalent thermal RC circuit. Furthermore, the effect of environmental humidity on the thermal characterization of active materials was isolated from the thermal impedance spectra.