Solid state fluoride ion batteries – FLUOBAT

Industrial, domestic or transport applications rely on instant access energy from static (power plants, large fuel cells) or mobile generators (batteries, small fuel cells). Among available electrochemical storage devices, much attention has been paid to rechargeable batteries notably due to their ability to store reversibly high energy content wheras a chemical vector is required for fuel cells (hydrogen, methanol …). Therefore, such electrochemical devices are considered as one of the most promising technologies for future societal challenges. However, improvements of the battery performances must be achieved to meet challenges in terms of energy density, cycle life, cost... In addition, one must consider the fact that for conventional Li-ion battery (LIB), the cost of lithium should drastically increase with the commercialization of the large-scale lithium-ion batteries. Consequently, the routes to succeed can consist in finding new classes materials and/or in considering new battery concept which allows reaching higher potentials and/or larger weight or volume capacities at low cost in safe and sustainable conditions. Remarkable performances are expected to be obtained with solid state fluoride ion batteries; these batteries use new cathode/anode couples based on the transport properties of fluoride ions. This concept of battery was proposed thirty years ago by Lucat 1 but didn’t give rise to significant commercial developments mainly due to poor ionic conductivities of the materials. Such a solid state fluoride ion battery is commercially available 2 but only for very specific applications as for oil and gas drilling. Recently, results obtained with nanostructured fluorides have given a renewed interest to this concept.3 These systems are indeed very attractive since from a theoretical point of view, they can deliver high potentials (3.0-5.0 V) and high energy content (1000-2000 Wh.kg-1 or 2000-5400 Wh.L-1). In such devices, a conversion process occurs between a metal fluoride (MFx) at the cathode and a metal (M’) at the anode (charged configuration) separated by a solid state fluoride ion conductor electrolyte; the full discharge leads to the reduction of MFx into the metal M and to the oxidation of M’ to the corresponding metal fluoride M’Fy. The use of fluoride ion batteries instead of conventional batteries suggests that it could lead to a significant breakthrough in the field of energy storage devices. The main goal of this project is to find the best constituting fluoride materials combinations (electrodes and electrolyte) in order to demonstrate the possible industrial developments of such solid state fluorides ion batteries. The research teams involved in this project are deeply involved for over several decades in the preparation and characterizations of new fluorinated compounds or in the field of electrochemistry of fluoride systems. In addition, the two involved industrial partners are well recognized as leaders in the field of batteries (Saft) and of Fluorine technologies (Rhodia, member of Solvay group). Thus, several tasks are identified, starting from the preparation and characterisations of fluorides to their evaluation as constituents in a fluoride ion battery. The expected results should provide global information to propose a prototype battery based on selected electrode and electrolyte materials. All components will be structured, eventually at the nanometer scale, to enhance the performances in terms of cell potentials, reversible storage capacities and cycle life. A scale-up of the materials elaboration is also scheduled.

1 C. Lucat, PhD thesis, Bordeaux, France (1976).
2 A. A. Potanin, Patent Application, WO 2006/112756, 2006.
3 M. A. Reddy, M. Fichtner. J. Mater. Chem. 21 (2011) 17059.