First efforts in MULTIMETALBAT were dedicated to systematically investigate Mg based electrolytes physico-chemical properties (ionic conductivity, cation solvation structure …) and the composition and thickness of the passivation layer formed onto Mg metal and better understanding their relationship with electrochemical performances of Mg metal anode. This was a crucial step in the design of any Mg based system such as Mg-Li since, up to date, Mg plating and stripping was thought to be impossible in the presence of any kind of passivation layer, significantly limiting the variety of electrolytes compatible with Mg metal anode. Three articles were published on this topic. In the first one, it has been demonstrated for the first time that high coulombic efficiency Mg plating and stripping can indeed be achieved in the presence of a stable passivation layer (J. Power Sources 626 (2025) 235711). As previously reported by the PI for Ca metal anode, the presence of borate based passivation layer was found to play an important role in the migration of divalent cations through the passivation layer.
In another article published this year (Batteries & Supercaps 2025, 00, e202500177) we investigated the surface chemistry and reactivity of magnesium electrodes with various organic solvents to improve understanding of passivation layer formation and its impact on rechargeable magnesium batteries (RMBs). Using X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry, we systematically studied Mg reactivity after immersion in ethers, alkyl and cyclic carbonates, esters, and nitriles investigating the composition of the formed passivation layer, demonstrating that the solvent type and immersion duration significantly affect its chemical composition, while the passivation layer thickness increase remains limited upon time of immersion.
Recently, we also published an article related to Mg metal anode using the commercially available salt Mg(TFSI)2, achieving electrochemical performances similar to the state of the art salt, Mg[B (hfip)4]2 (Adv. Energy Mater. 2024, 2401587). The latter being notoriously difficult to synthesize with acceptable purity. Three important parameters controlling Mg plating and stripping reversibility have been identified: i) The role of the cation solvation shell in solution, with the presence of ion pair (present at relatively high salt concentration) being highly detrimental, ii) the us of titanium substrate with similar crystal structure and lattice parameter as Mg was found to result in lower nucleation overpotential and better kinetics and iii) the use of dibutyl magnesium (Mg(butyl)2) was found to enable the formation of thinner passivation layer but more importantly this work highlighted the role of Mg(butyl)2 as an anion complexing agent, favoring the mobility of electroactive cationic species, paving the way toward better electrolyte design with improved cation transference number.
In parallel, the design of suitable cathode active materials compatible with multications systems have been explored. A first family of such active material have been identified in collaboration with Dr. M. Unterlass (Fraunhofer Institute for Silicate Research ISC) and hybrid materials (HMs) combining the functionalities of organic compounds (such as organic pigment molecules) with typical inorganic host structures, such as TiO2 was reported (Small Struct. 2024, 5, 2400074). These layered HMs were found to present excellent performances in lithium-ion batteries and are now being considered (together with new classes of HMs) as cathode materials for multication batteries.
