A New Generation of High Energy Carbon/Carbon Supercapacitors in Environment Friendly Electrolytes (Supercapacitors Europe 2014)

Most of the commercially available electrochemical capacitors are based on activated carbon (AC) electrodes in an organic electrolyte, e.g., tetraethylammonium tetrafluoroborate in acetronitrile or propylene carbonate. The reason of this choice is linked to the high voltage (2.7-2.8 V), and consequently high energy density, which is reached with these electrolytes as compared to conventional aqueous electrolytes, such as KOH or H2SO4 solutions, where the maximum voltage is lower than 0.8 V. Recently, we have shown that voltage values up to 1.6-1.8 V can be reached with AC/AC systems in salt aqueous electrolytes, such as alkali sulfates or nitrates, giving promising perspectives for low cost, safe and environment friendly devices.

This presentation looks at the development of an optimized prototype based on salt aqueous electrolytes, using realistic materials. The selected current collectors are made from stainless steel which has been surface treated in order to improve the contact resistance. Since the voltage reached in the salt media is lower than in organic electrolyte, we have paid attention to the enhancement of capacitance by adding pseudo-capacitive contributions to the EDL capacitance. In particular, the addition of corrosion inhibitors to the electrolyte allows simultaneously to enhance the maximum potential of the positive electrode and to provide a pseudo-faradic redox contribution. The EDL capacitance has been improved by adjusting the porosity of the carbon electrodes to the size of electrolyte ions; carbons obtained by self-activation of biomass were found to present pores fitting the size of ions, with much narrower pore size distribution than the traditionally prepared activated carbons. Overall, by combining appropriate materials and aqueous electrolytes, we were able to design an AC/AC capacitor reaching the same energy density as in organic medium.

François Béguin was Professor and leader of the Energy&Environment Group in Orléans University (France) till 2011, and he is now Professor in Poznan University of Technology (Poland), where he has been awarded the WELCOME stipend from the Foundation for Polish Science.

His research activities are devoted to chemical and electrochemical applications of carbon materials, with a special attention to the development of nano-carbons with controlled porosity and surface functionality for applications to energy conversion/storage and environment protection. The main topics investigated in his research group are lithium batteries, supercapacitors, electrochemical hydrogen storage, reversible electrosorption of pollutants. He owns several patents related with the synthesis of nano-structured carbon materials (nanotubes, carbons from biomass, ...) and their use for electrochemical systems. He published over 260 publications in high rank international journals and his works are cited in 12000 papers. His Hirsch index is H = 52.

He is also involved in several books dealing with carbon materials and energy storage. Recently, he edited the book "Supercapacitors - Materials, Systems and Applications. He is a member of the International Advisory Board of the Carbon Conferences and he launched the international conferences on Carbon for Energy Storage and Environment Protection (CESEP). He is member of the editorial board of the journal Carbon.

In the French Agency for Research (ANR), he was Director of national programs on Energy Storage and Hydrogen and Fuel Cells till 2012.

Poznan University of Technology (PUT) consists of ten faculties and provides didactics for about 21 thousand students. PUT offers Bachelor, Master and Doctorate courses in Polish and English. The Faculty of Chemical Technology, with about 1500 students (including PhD studies), is one of the most dynamic faculties and consists of two institutes. The "Power Sources Group" of Professor Béguin belongs to the Institute of Chemistry and Technical Electrochemistry (ICTE) and has a long-term experience in the development of nanostructured materials and their applications for chemical and electrochemical systems (e.g. supercapacitors, Li-ion accumulators, hydrogen storage, fuel cells, sensors and trapping of pollutants).