Context - Objectives

CONTEXT

BatteriesElectrochemical capacitors are energy-storage devices that are ideally suited for rapid storage and release of energy. Compared with conventional capacitors, the specific energy density of these devices is several orders of magnitude higher. They also have a higher specific power density than most conventional batteries. Among the various types of electrochemical capacitors, electrochemical double layer capacitors (EDLCs) are very promising for use in high power electronic devices and electric vehicles . These systems are based on the adsorption of ions forming the double layer at the electrode/electrolyte interface where charges accumulated by the electrode are compensated by electrolyte ionic species of opposite charges. High surface area carbons are generally used as the capacitive material because of their low cost, excellent cycle life and high specific surface area due to their micro/mesoporous structure.
Supercapacitors are now invading many fields of nowadays life due to their high power capability coupled with fair energy density. They can be found in stationary devices (gravitational potential energy in harbor cranes and elevators, uninterrupted power supply UPS, etc) or in applications related to transportation. Several trains, tramways, buses, cars, are powered by supercapacitors coupled (or not) with batteries or many other energy storage or conversion devices (fuel cells, thermacalendering machinel engine, etc…). Supercapacitors have enabled the rise of many innovations in the field of transportation whose number is now increasing due to the attractive long term cycle life of supercapacitors. Garbage collecting trucks running on small range distances with many starts and stops are targeted by the use of supercapacitors for example. In Nice, a new innovative electrical bus has been launched at the Nice International airport. This bus is charged in 10 seconds at each station leading to an autonomy of 800 meters thanks to supercapacitor modules. Extra batteries are installed on board for 30 km range extension in case of emergency or to drive toward the parking station.
However, one of the major requirements for such applications (Start & Stop systems in cars, load leveling devices in tramways, etc…) is that supercapacitors have to fit a restricted volume inside the vehicles. Only in aircraft and space industries are the requirements based on gravimetric energy density. In other applications, the volumetric energy density is more critical. Indeed, ground transportation aims at decreasing the volume related to auxiliary equipment (engine, cooling, storage, etc…) to leave more space available for carrying people, goods, merchandises, etc… The same requirement applies for stationary devices in which the volume of the energy storage device is limited (UPS for example) but which require the maximum energy in such a given volume.

The main drawback of commercial supercapacitors is that the use of very low density activated carbons (less than 1 g/cm3) as electrode materials prevents the fabrication of high volumetric energy devices. This low density is an intrinsic characteristic of activated carbons that are designed with a high surface area, i.e. a pore size distribution aiming at mesopores and micropores domination with a high cumulated pore volume. Furthermore, the only way to improve the volumetric energy density of carbon based devices is to use flammable organic based electrolytes (mostly acetonitrile) that enhance the cell voltage (up to 3.0V) at the cost of supercapacitor safety. As a matter of fact, commercial devices using activated carbon together with acetonitrile based electrolytes are those implemented in various applications listed above. winding machineNonetheless, while keeping the same components, it seems difficult to improve the volumetric energy density or to increase the safety of such devices. One way to achieve this goal is to increase the cell voltage (up to 3.5 or 4.0V) by the use of alternative organic solvents or ionic liquids (but at what cost in terms of power and safety?) . The second way is to use denser electrode materials, such as metal oxides, to replace carbon based electrodes . This is the research path that we will address within IVEDS project (Improving the Volumetric Energy Density of Supercapacitors): the design of oxide-based supercapacitors with enhanced energy density while keeping both high power density and long term cycling ability. This goal will be accompanied by a safety enhancement since these materials will be operated in aqueous-based electrolytes. Although, pseudocapacitive oxides have already been considered as electrode materials and tested as full devices in asymetric configurations when coupled with an EDLC carbon electrodes, this concept should move a step forward with the design, fabrication and benchmarking of innovative supercapacitors including two metal oxide based electrodes, with unprecedented high volumetric energy densities. This will lead to a major breakthrough in the field of supercapacitors.



OBJECTIVES

IVEDS project aims at the design of safe and high volumetric energy electrochemical capacitors and the concomitant benchmarking of various asymmetric devices. Our final goal is to increase by 50% the volumetric energy density of nowadays symmetrical carbon ECs, while keeping the power density close to that of state of the art devices.

Three key players in the field of supercapacitors (IMN, ICGM) and benchmarking of lithium-ion batteries (LRCS) are gathering together in this innovative project which will target a change of paradigm from carbons to oxides for large-scale applications of supercapacitors where volumetric energy density and safety are the moRS2Est important parameters. This consortium will take benefit from its belonging to the French Network on Energy Storage (RS2E - http://www.energie-rs2e.com/fr).

The project is expected to provide basic knowledge on the role of solid state chemistry on the electrochemical performance of oxides as supercapacitor electrodes. This fundamental research will be used to implement more applied research based on the preparation of nanocomposite electrodes that adequately combines the active material to a high electronically and ionically conductive architecture based on carbons. This will demonstrate how an attractive oxide can be turned into a performing electrode. Finally, the selection of chemistries and architecture/formulation will be done by the three partners in order to push the project from its fundamental side to a more applied field. Formulation of oxide based electrodes for casting current collectors and integration in industrial prototypes has been poorly investigated up to now. It will provide valuable data both for researchers who hardly feature how their new materials behave at a cell scale, and for potential users who might like to know what can be expected from oxide based electrodes in a real cell. This comes together with a strategy for dissemination of the results to different potential industrial partners, from materials manufacturers to end-users.