Button cell supercapacitors with monolithic carbon aerogels

Carbon aerogels are highly porous materials prepared via pyrolysis of resorcinol-formaldehyde aerogels. The density of the aerogels can be varied in a wide range, whereby the major part of the pores is accessible to ionic conductors. Therefore, the application of high surface area aerogels as electrodes in supercapacitor devices is promising. In the present publication, the integration of thin monolithic aerogel composites in button cell casings is presented. The preparation of thin and mechanically stable aerogel electrodes was performed via integration of carbon fibers into the aerogel skeleton. In order to increase the external electrode area in the button cells (volume: 2.1 cm(3)) a special folding technique for the electrodes (thickness: 180 mum) was employed. The aerogel capacitors exhibit an excellent long term stability with no significant degradation after 80,000 charging and discharging cycles. According to a ragone-evaluation of the impedance data, the maximum power output and energy content for the aerogel button cells are 4.6 W and 4.9 mWh, respectively. The influence of CO2-activation on the capacitive and resistive behavior of the electrodes in different aqueous electrolytes is analyzed using innovative analytical methods for cyclic voltammetry and impedance spectroscopy. (C) 2002 Elsevier Science B.V. All rights reserved.