Periodic Reporting for period 1 - MULTIMETALBAT (Multi-metal anode: Towards safe and energy dense batteries)
Periodo di rendicontazione: 2023-06-01 al 2025-11-30
Li metal is considered to be the holy grail anode material due to its high specific capacity and low standard
redox potential and could, in theory, lead to the assembly of extremely high energy density cells. Metal anode
based batteries, in general, represent the main viable option towards a leapfrog in terms of energy density when
compared with current Li-ion technology, thus motivating important research efforts in Li-air, Li-Sulfur and,
more recently, solid state batteries (SSB). Unfortunately, all of these technologies (even SSB) suffer from
dendritic Li growth, eventually resulting in short circuit/thermal runaway. Requirements for smooth Li
metal electrodeposition, mostly consist in the fine control of the cation mass transport through the solid
electrolyte interphase (SEI), which in turn is governed by the composition, morphology and stability of the
latter. Unfortunately, and after several decades of investigation, it is virtually impossible to achieve the perfect
interphase/interface which can sustain thousands of cycles in real battery operation conditions. The main
objective of MULTIMETALBAT is to bring a new paradigm for metal anode by developing electrolytes
containing a mixture of multiple cations (Li+, Na+, K+, Ca2+ or Mg2+) which will modify the overall
thermodynamics of plating and stripping when compared with conventional single metal anode. Kinetic
competition between various electrodeposition processes will be promoted and the SEI will be engineered to
sustain high mechanical, chemical and thermal stability, hence helping promoting homogeneous cation
diffusion through it. Targeted figures of merit include: i) critical current density for 3D metal growth above
10 mA.cm-2 and ii) 350 Wh/kg energy density for 100 mAh pouch cells, almost doubling that of current Li-ion.
Yet, the main objective of MULTIMETALBAT will be increased safety and extensive standard safety
measurements will be performed on prototype cells and compared with Li-ion batteries.
redox potential and could, in theory, lead to the assembly of extremely high energy density cells. Metal anode
based batteries, in general, represent the main viable option towards a leapfrog in terms of energy density when
compared with current Li-ion technology, thus motivating important research efforts in Li-air, Li-Sulfur and,
more recently, solid state batteries (SSB). Unfortunately, all of these technologies (even SSB) suffer from
dendritic Li growth, eventually resulting in short circuit/thermal runaway. Requirements for smooth Li
metal electrodeposition, mostly consist in the fine control of the cation mass transport through the solid
electrolyte interphase (SEI), which in turn is governed by the composition, morphology and stability of the
latter. Unfortunately, and after several decades of investigation, it is virtually impossible to achieve the perfect
interphase/interface which can sustain thousands of cycles in real battery operation conditions. The main
objective of MULTIMETALBAT is to bring a new paradigm for metal anode by developing electrolytes
containing a mixture of multiple cations (Li+, Na+, K+, Ca2+ or Mg2+) which will modify the overall
thermodynamics of plating and stripping when compared with conventional single metal anode. Kinetic
competition between various electrodeposition processes will be promoted and the SEI will be engineered to
sustain high mechanical, chemical and thermal stability, hence helping promoting homogeneous cation
diffusion through it. Targeted figures of merit include: i) critical current density for 3D metal growth above
10 mA.cm-2 and ii) 350 Wh/kg energy density for 100 mAh pouch cells, almost doubling that of current Li-ion.
Yet, the main objective of MULTIMETALBAT will be increased safety and extensive standard safety
measurements will be performed on prototype cells and compared with Li-ion batteries.
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.
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.
1. The work on Mg(butyl)2 for Mg metal anode. This article highlighted the possibility for large anions to be coordinated in the electrolyte. This finding have great implications since it paves the way towards designing electrolytes in which anion mobility can be limited favouring the migration of cations (the electroactive specie) and thus homogeneity of metal plating and power performances of the battery. This publication calls for a new battery research domain targeting new anion complexing agents.
2. Finding that titanium substrate constitutes an excellent current collector for Mg electrodeposition. The low lattice mismatch between Ti and Mg enabled a much better reversibility of Mg plating (higher coulombic efficiency and lower voltage hysteresis between plating and stripping) and better adhesion of Mg deposit. While most publication on Mg plating use non-realistic substrates such as platinum and gold, finding an effective non-noble metal substrate open the door to metal anode free Mg based batteries. This work also highlighted the crucial role of the quality of the nucleation process and its impact on coulombic efficiency and adhesion of the metal deposit.
2. Finding that titanium substrate constitutes an excellent current collector for Mg electrodeposition. The low lattice mismatch between Ti and Mg enabled a much better reversibility of Mg plating (higher coulombic efficiency and lower voltage hysteresis between plating and stripping) and better adhesion of Mg deposit. While most publication on Mg plating use non-realistic substrates such as platinum and gold, finding an effective non-noble metal substrate open the door to metal anode free Mg based batteries. This work also highlighted the crucial role of the quality of the nucleation process and its impact on coulombic efficiency and adhesion of the metal deposit.