Patrice Simon

Electrochemical Characteristics and Impedance Spectroscopy Studies of Carbon-Carbon Supercapacitors

This paper presents the results obtained on the electrochemical behavior of electrochemical capacitors assembled in nonaqueous electrolyte. The first part is devoted to the electrochemical characterization of carbon-carbon 4 cm 2 cells systems in terms of capacitance, resistance, and cyclability. The second part is focused on the electrochemical impedance spectroscopy study of the cells. Nyquist plots are presented and the impedance of the supercapacitors is discussed in terms of complex capacitance and complex power. This allows the determination of a relaxation time constant of the systems, and the real and the imaginary part of the complex power vs. the frequency plots give information on the supercapacitor cells frequency behavior. The complex impedance plots for both a supercapacitor and a tantalum dielectric capacitor cells are compared.

Studies and characterisations of various activated carbons used for carbon/carbon supercapacitors

Various activated carbons from the PICA Company have been tested in supercapacitor cells in order to compare their performances. The differences measured in terms of specific capacitance and cell resistance are presented. Porosity measurements made on activated carbon powders and electrode allowed a better understanding of the electrochemical behaviour of these activated carbons. In this way, the PICACTIF SC carbon was found to be an interesting active material for supercapacitors, with a specific capacitance as high as 125 F/g.

Polythiophene-based supercapacitors

Abstract Polythiophene (Pth) and polyparafluorophenylthiophene (PFPT) have been chemically synthesized for use as active materials in supercapacitor electrodes. Electrochemical characterization has been performed by cyclic voltammetry and an electrode study has been achieved to get the maximum capacity out of the polymers and give good cyclability. Specific capacity values of 7 mAh g −1 and 40 mAh g −1 were obtained for PFPT and polythiophene, respectively. Supercapacitors have been built to characterize this type of system. Energy storage levels of 260 F g −1 were obtained with Pth and 110 F g −1 with PFPT.

Activated Carbon/Conducting Polymer Hybrid Supercapacitors

This paper presents the work carried out within a European Union (EU) project which led to the development of 3 V and 1.5 kF preseries supercapacitor modules and 2 kW stacks based on hybrid cells with poly(3-methylthiophene) as positive electrode and activated carbon as the negative electrode with propylene carhonate-tetraethylammonium tetrafluoroborate electrolyte. These prototypes, which display a concept of hybrid cell operating with a high-surface-area activated carbon and a conventional electronically conducting polymer, both commercially available, and with a nontoxic and nonvolatile electrolyte, provide a successful response to the market demand for high power and energy supercapacitors operating with an environmentally friendly electrolyte.

Hybrid Supercapacitors Based on Activated Carbons and Conducting Polymers

A new concept of hybrid supercapacitors has been designed with a conductive polymer as the positive electrode and activated carbon as the negative electrode. The chosen polymer was poly(4-fluorophenyl-3-thiophene) or P-4-FPT, whose good doping properties are well known Several activated carbons were tested, and the results reported here were obtained with carbons from Spectracorp (BP25 and YP17). The mass ratio of active materials was calculated to obtain the maximum cell voltage (3 V). The system studied in our laboratory was 4 cm 2 test cells which reached 48 Wh/kg of maximum energy associated with 9 kW/kg of maximum power (considering the mass of the active materials). Industrial prismatic prototypes were then assembled, containing 60 cm 2 electrodes. These prototypes reached a maximum energy of 7.5 Wh/kg (total mass), and a maximum power of 250 W/kg.

Electrode compositions for carbon power supercapacitors

The purpose of this work was to prepare economically-large electrodes in order to assemble mono-element supercapacitors with a capacity of more than 300 F and to reach powers in the range of 125 W (2 V/element) with the selected structure. In this paper, results are presented from different binder compositions—PTFE and a mixture of CMC/PTFE—that were tested in order to increase the volumetric capacitance of the electrode. The electrode composition was adapted to each binder composition used. For cost reasons, the amount of PTFE was reduced and the mixture of CMC/PTFE was examined as a cheaper alternative. We have obtained more than 25 F cm−3 per electrode, with a time constant close to 3 s, and power outputs compatible with automotive applications.

Electrode optimisation for carbon power supercapacitors

The purpose of this work was to economically prepare large electrodes (32 cm2) in order to assemble mono-cell supercapacitors (100 cm3) of 250 F and to reach powers in the range of 120–130 W (2 V/cell) with the structure selected. We have reached more than 20 F/cm3 of electrode, with a time constant of a few seconds (close to 2 s) and reached powers compatible with starting applications.

Chemical synthesis and characterization of fluorinated polyphenylthiophenes: application to energy storage

Some fluorinated polyphenylthiophene have been chemically synthesized with good yields. The characterization of their positive and negative doping processes was performed by cyclic voltammetry and showed high capacities, but proved no real stability in cycling experiments. The application of the P-4-FPT as electroactive material in supercapacitor systems showed interesting properties in term of energy and power delivered.

Possible improvements in making carbon electrodes for organic supercapacitors

Abstract Properties of an Electrical Double Layer Capacitor depend both on the technique used to prepare the electrode and on the current collector structure. Capacitors can be built in a similar way to prismatic cells, with several electrodes connected in parallel for each polarity. Our Electrical Double Layer Capacitors included several carbon/carbon electrodes and all the components (electrodes and separators) were wetted with an organic liquid solvent containing a quaternary ammonium salt as electrolyte. In the present work, electrodes were prepared by two different ways: the first one consisted in spraying a liquid suspension of the electrode materials on a nickel foil, and the second one which consisted in filtering and pressing the electrode materials on to nickel collectors. The first technique allowed us to build seven capacitors of 600 F–2.5 V, with time constants of 12 s. Two banks with series connected supercapacitor cells, one as a 12 V–100 F bank and the other one as a 15 V–85 F were tested on cycling. In our experiments to test these banks of supercapacitors, we also coupled the 100 F–12 V bank to a 12 V–7 Ah secondary lead–acid battery in order to demonstrate the contribution of the supercapacitors during power peaks. Comparing the two techniques used to make the electrodes in terms of performances obtained on the supercapacitors prepared, we obtained the best results by using the second method of electrode preparation. Moreover, two kinds of nickel collectors were studied: expanded nickel grids—and various grades of nickel foams, nickel foams giving the best results. The Equivalent Series Resistance of the electrodes prepared with nickel foams depends on nickel foam grade; it is observed to be 1.75 Ω for a capacitance of 1.37 F in our experimental set up, leading to a time constant of 2.4 s. The mechanical properties of the electrodes were improved as well.

Multi electrode prismatic power prototype carbon/carbon supercapacitors

Abstract This work describes the fabrication and the characterization of low-cost 2 V carbon/carbon power supercapacitors. Each cell had a volume of 100 cm 3 . Three 2 V-supercapacitors were assembled and tested under different currents and at different temperatures. The measurements have shown a specific power of 1.1 kW/kg, a volumetric capacitance of 25 F/cm 3 per electrode and a time constant of 2 s.