Calorimetric measurement of the heat generated by a Double-Layer Capacitor cell under cycling

A calorimetric technique was developed for measuring heat generated within a Double-Layer Capacitor cell under cycling by analyzing its transient temperature change. Measurements were performed for a short time period of the current cycle to get small temperature changes and thus not substantially affect the properties of the cell during charge and discharge. The calorimetric technique is described and its performance demonstrated on a symmetrical activated carbon cell with 1 M N(C2H5)4BF4 in propylene carbonate as electrolyte over a wide current range. Capacitance of the cell at room temperature was around to 0.25 F cm−2. Power density was found between 2 × 10−3 to 70 × 10−3 W cm−2 according to the current density that varied between 0.01 and 0.15 A cm−2 for a cell load pressure equal to 25 kg cm−2. Equivalent resistance, measured on the calorimeter, was found to vary between 4 and 8 Ω cm2, according to the charge rate. Calorimetric measurements were found in good agreement with the energy balance of the cell deduced from the potential profiles and currents.