Online proceedings - EDA Publishing Association

24-26 September 2008, Rome, Italycycles. First, a calorimetric technique was developed formeasuring the heat generation rates of the EDLCs undercycling. The as developed technique is described.Measurements performed on carbon cells are presented as afunction of current cycles and compared with values givenby a porous electrode model of double layer capacitance.II.EXPERIMENTALA calorimetric technique was developed for measuringpower dissipated by EDLCs under cycling. Experimentswere conducted in a home-made heat conduction calorimeteras shown in Figure 2. The technique consists in analyzing thetransient temperature response of the EDLC cell afterapplying a series of charge and discharge current. Then,average power is obtained by fitting the temperature responsegiven by a three-dimensional heat diffusion model andcalculated by the Finite Elements Method (Comsol-Multiphysics Software) after meshing the full structure of thecalorimeter.The cell is pressed between two heat-flow-meters having topand bottom sides in contact with a cold plate controlled atfixed temperature by a fluid circulator (see Figure 2). Thecell is incorporated within a small annular enclosurecontaining the relevant liquid electrolyte. Air tightness wasensured to avoid the contamination and evaporation of theelectrolyte. The cell is axially compressed to a given contactpressure. Each heat-flow-meter is constructed with a cylinderin polymer where 8 type K thermocouples connected inseries are attached to the side in contact with the cell undertest. The two cold plates form the cold junction of thethermocouples. Each heat-flow-meter exhibits a sensitivity ofapproximately 320µV.K -1 between 0 and 100°C. Atemperature change as low as 5 x 10 -3 °C can be detected.Minimum detectable power was 50 µW for a cell of 30 mmin diameter.The as developed apparatus is suitable for cells with adiameter ranged from about 15 to 40 mm. Tests can beperformed with different loading pressure and liquidelectrolytes.b) Heat flow-meter, as fabricated, with 8 thermocouplesFigure 2: Home-Made heat conduction calorimeter for measuring heatgeneration rates in Electric Double-Layer capacitors under cyclingFigure 3b and 3c represent the cell voltage and temperatureas measured as a function of time after applying a charge anddischarge current of 0.4 A for 2 Volt as potential window ona carbon cell with electrolyte (propylene carbonate with Net 4BF 4 ,1M.L -1 ). Capacitance and average thermal power of thecell were found to 1.8F Farad and 0.19 Watt, respectively.Figure 4 shows the temperature distribution, as calculated bythe Finite Elements Method, within the calorimeter at 250stime after applying the current cycle presented in Figure 3a.Thermal modeling was found in quite good agreement withthe experiment (see Figure 3c)Current (A)0,40,20,0-0,2-0,40 50 100 150 200 250Time (s)ChargeDischargea) Current applied as a function of time as measured2,0Voltage (V)1,51,00,50,0a) Experimental apparatus0 50 100 150 200 250Time (s)b) Cell voltage as a function of time as measured©EDA Publishing/THERMINIC 2008 225ISBN: 978-2-35500-008-9