A new concept of Proton Battery – H-BAT

In the current context of global warming, there is an urgent need to mobilize French research resources to reduce greenhouse gas emissions by accelerating the energy transition to renewable energies on the one hand and developing energy storage capacities on the other hand,. For new, efficient, sustainable and safe electrochemical storage systems, the choice of the charge carrier is fundamental. It must be a light and abundant element with an excellent ionic conduction in the accumulator’s materials. The proton/hydrogen couple fulfills these requirements in aqueous media but it nevertheless has limitations related i) to electrode corrosion and ii) to the electrochemical window of water which limits the density of energy.

H-BAT proposes a new concept of proton conduction batteries using as electrolyte a non-corrosive protic ionic liquid (PIL) associated with high-capacity negative electrodes (light metal hydrides) and high-potential positive ones (V and Fe phosphates). Ionic liquids (ILs) are room temperature molten salts, thermally stable and therefore safe, with an electroactivity window up to three to four times larger than that of water. Their reactivity is different of that of aqueous media, therefore limiting corrosion phenomena. Compared to aprotic ionic liquids (AILs), the PILs take advantage of having mobile protons, being inexpensive to prepare with a reproducible synthesis method controlled by LISE, and exhibiting ionic conductivities compatible with use as electrolytes (> 1 mS/cm). In addition, the use of a PIL as electrolyte will permit to implement large capacity hydride alloys for the negative electrode, in order to reach a strong increase in the specific capacity, while preventing the use of critical materials. The elaboration of the considered Mg-based or TiFe-type alloys is a strong know-how at ICMPE. The width of the electrochemical window will allow to use a positive electrode working at high potential, leading to a significant gain in energy density compared to current aqueous batteries. ICMCB masters the synthesis of these materials such as phosphates.

H-BAT is a fundamental project aiming at developing an innovative battery concept, at understanding the proton transfer mechanisms between the electrolyte and the electrodes and at finely describing the interfaces between PILs and electrodes. To reach these goals, the project is divided into four tasks. Tasks 1 and 2 are dedicated to the synthesis and characterization of PIL on the one hand, and electrode materials on the other hand, and will enable to identify the key criteria for the selection of the PILs adapted to each family of positive and negative electrodes studied. Task 3 is entirely devoted to understanding the interfaces, on the one hand with the experimental study of the growth, stability and role of the solid-electrolyte interface (SEI) - in particular on the transfer of protons between PIL and electrode materials by implementing operando analysis techniques, and on the other hand with the modeling of the properties of interfaces and interactions to get a detailed mechanism of proton transfer. This work will culminate in Task 4 with the establishment of a proof of concept of the complete battery. Ultimately, this project aims to develop a totally innovative electrochemical system combining elements (electrodes, electrolyte) that have never been previously assembled, with a high energy density.

The three partners combine strong complementary expertise on PIL, positive and negative electrode materials, which represent an asset to make this project a success and to place the research teams involved in a leading position in this scientific field.