Exploitable results
In this programme, the synthesis and activation conditions of new materials (carbon aerogel, high surface carbon black and P-Novolaks) were studied in detail. For all these carbon materials, large improvements were obtained in terms of synthesis and activation time as well as in the yield of the overall process leading to a process definition quite comparable to the ones used for other existing commercial materials and to a prospective production cost of the same range. This work enabled the production of carbon materials at the kilogram level with significant increase of the specific surface area, first order parameter for super-capacitor applications (from >800 m2/g to >1700 m2/g). These materials delivered specific capacitances at the same level as the best materials on the market and displayed a high conductivity compared to commercial existing products (about four times higher in some cases).
The analytical study of the carbon performances has also emphasised the close relationship between the pore size distribution, active surface area and electrochemical behaviour. As a positive output of this project, this study provides tools for a comprehensive choice of carbon materials allowing a better and easier tuning of these materials for future applications.
New polymer organic electrolyte systems were elaborated and used in super-capacitor cells together with the carbons synthesised during this contract. The comparison of these polymer systems with liquid ones showed a lower power capability of the polymer systems due to their lower ionic conductivity. However, advantages were detected in terms of fading or self-discharge.
The main problem encountered in this programme was the use of these carbon materials in an industrial electrode structure and further work is needed in order to improve the adhesion of the coating on the current collector. However, super-capacitor cells built using these materials demonstrated improved performances in terms of life cycle for voltages as high as 3V compared to 2.3V usually specified by the super-capacitor manufacturers.
As a final output of this programme, the progress made in the comprehension of the electrochemistry of the system, in the interaction of the electrolyte with the active materials has contributed to develop a new cell generation with improved performances especially in terms of self-discharge and life cycle. The specific energy level is found close to 8Wh/kg and is closer to the goal than before (4Wh/kg). For power performances, the level is around 3-5kW/kg and well above the stated goal.
The benefits of this new technology are foreseen in a wide field of applications, ranging from electric vehicles and hybrid vehicles to public transportation, power quality, actuators and satellites. This will help bring new and reliable technological solutions that will contribute to solve environmental and economical problems. Aside from these benefits, this new technology will also have a significant impact on European employment levels. Production levels of several million super-capacitor unit cells per year are expected by 2005. For these reasons, super-capacitors are of strategic importance for the European industry and the pursued efforts have allowed to bring technological leadership.