Water-based magnesium innovative energy storage – MAGWAT

Water-based solutions play a key role in the realm of biology, chemistry, and more particularly, in energy-related fields such as photo and electro-catalysis and batteries. While aqueous batteries were believed to be constrained by the thermodynamic electrochemical stability window of water (1.23 V vs. NHE under standard conditions in absence of kinetics phenomena), this is no longer true thanks to water-in-salt electrolytes (WISEs). This concept, implying highly concentrated aqueous solutions, led to an extraordinary increase in the operational potential window of aqueous lithium batteries. This enhancement is mainly explained by the absence of free water molecules and by the crucial role of the anion-based interface in the Helmholtz’ layer. While water-in-salt electrolytes open the possibility to design competitive and sustainable electrochemical systems; yet, these solutions are generally formulated by using expensive and toxic salt, and the fundamental science behind this WISE concept still needs to be rationalized, to date. To widen the spectrum of chemistries and to look at more sustainable elements or salts, one can imagine the formulation of WISE using multivalent cations, such as magnesium, which is safer, less expensive and more abundant than lithium.
Nevertheless, according to the sole state-of-the-art, the use of Mg-based WISE in rechargeable aqueous battery improves only slightly its operational potential window to 2.0 V, without clearly reporting proper electrochemical mechanisms under cycling, limiting thus our understanding on such a system. Hence, this project aims at developing innovative and more sustainable electrolytes solutions for Mg batteries to improve then the potential window of rechargeable Mg aqueous batteries. To reach this main objective, a perfect understanding of the key role of the electrolyte and of the interface chemistry is crucial and calls upon unprecedented fundamental insights into the reactivity of water-in-salt solutions.
The main goal of MAGWAT is to determine whether Mg aqueous batteries based on concentrated salts are a viable future technology. Precisely, the objectives of the project are to: 1) fundamentally understand the reactivity of concentrated aqueous solutions based on Mg salts compared to those based on Li, 2) apprehend the phenomena occuring in the bulk of the electrolytes and at the battery interfaces and 3) propose and develop innovative electrolytes to resolve the relative low solubility of Mg salts in water. We will achieve these objectives firstly by following a multiscale comprehensive approach, including pioneering experiments, such as radiolysis and synchrotron X-Ray spectroscopy coupled with computational studies, providing thus key electrolytes physical properties. This fundamental knowledge will be then further used to design innovative electrolyte solutions to control and engineer the battery interfaces. By following this approach, we expect to increase the operational potential window of targeted rechargeable aqueous Mg batteries and to initiate the development of appropriate positive and negative electrodes.
Altogether, by designing rechargeable batteries based on Mg and water, we will move towards the development of ecologically friendlier and safer technologies, using more abundant and less hazardous materials than current Li-ion batteries. Additionally, the breakthroughs in the fundamental knowledge and innovative strategies will also impact other battery chemistries and energy storage-related fields such as supercapacitors and catalysis, opening the door for green and safe energy storage.