Identification of thermal process of electric double layer capacitor systems by distribution of relaxation times analysis for thermal impedance spectroscopy

Identification of thermal process is important for obtaining the thermal parameters of electric double layer capacitors. This study applies distribution of relaxation times (DRT) analysis for physical interpretation of the thermal impedance spectroscopy measurement of EDLC systems. Three distinct peaks are observed in the DRT plots of the electrode systems. The peak area represents the thermal resistance contribution of different thermal processes, while the time constant of peak center represents the speed of each process. The results indicate that the peaks from short to long time constant can be attributed to heat conductions in solid, interfacial, and fluid-involved paths, respectively. In addition, the area of peaks are strongly affected by the compression of electrode. This is attributed to the variations in total thickness and cross-sectional area of the system. Finally, replacing the fluid from air to electrolyte or changing solid–fluid ratio in two-phase region can lead to a remarkable shift in time constant of fluid-involved heat transfer peak.