Online proceedings - EDA Publishing Association

24-26 September 2008, Rome, ItalyElectro-thermal analysis of Electric Double-Layer-CapacitorsPh. Guillemet, C. Pascot, Y. ScudellerUniversité de Nantes, Ecole Polytechnique, LGMPA, La Chantrerie, rue Christian Pauc, BP 50609, 44306 Nantes Cedex 3,FranceAbstract-. Electric Double Layer Capacitors (EDLCs)operate between rechargeable batteries and electrolyticcapacitors with respect to energy and power performance.Prediction of internal heating due to discharge and chargecurrent cycles is one of key elements for producing reliableand safe devices with long cycle-life. A calorimetrictechnique was developed for measuring the heat generationrates of EDLCs under cycling. The as developed technique isdescribed. The heat generation rates were measured oncarbon cells as a function of current cycles. Thermalmeasurements were found in quite good agreement with aporous electrode model of double layer capacitancedescribing the charging mechanisms. Calculations wereperformed after estimating the electrical properties of the cellby fitting the dynamic cell voltage. Investigations haveconducted to a better understanding of the electro-thermalbehavior of EDLCs.I. INTRODUCTIONElectric Double Layer Capacitors are used as energy storagedevices in electronics as well as primary and secondarypower sources in numerous applications. Most attractiveapplications are the power back-up for memory functions,the peak power assistance to reduce the duty-cycle on thebattery, the temporary energy storage in the ElectricVehicles. Such devices operate between rechargeablebatteries and electrolytic capacitors with respect to energyand power performance [1, 2, 3].Electric Double Layer Capacitor construction is shown infigure 1. A unit cell consists of two porous carbon electrodeswith a separator between them wetted with an electrolyte.Electrode has thickness in the range 50-500 µm. Electrode iscoated with a metal current collector (see Figure 1).Electrical charge is stored at the interface between a highsurface-areacarbon electrode and a liquid electrolyte thoughelectrostatic interactions. The surface area, in the range ofthousands of square meters per gram of active material,creates a high capacitance. The storage process is highlyreversible. The charge-discharge cycle can be repeatedvirtually without limit by delivering a high power densitywith a large repetition rate. A device is formed of multiplelayers with dimensions that can vary from a fraction ofmillimeter to a couple of centimeters, in a variety ofpackaging depending on capacitance values.During the charge processes, current flowing through theporous structure causes internal heat generation and thenundesirable overheating and temperature change.Enhancement with respect to performance, reliability andsafety of capacitors need a better understanding of electrothermalof charging mechanisms. Multi-physics models mustbe developed to predict heat generation rate and temperaturein a wide range of operating conditions.Figure 1: Electric Double Layer Capacitor constructionThis paper investigates the electro-thermal behavior of theElectric Double Layer Capacitors. The objective is to predictthe internal heating due to discharge and charge current©EDA Publishing/THERMINIC 2008 224ISBN: 978-2-35500-008-9