High capacity and innovative magnesium-ion batteries based on nanostructured negative electrodes – MAGICIEN

The methodology used is based on the discovery of new materials, the deep understanding of their electrochemical behavior and the optimization of their performance. Combination of different metals and nanostructuration are powerful methods to obtain required properties of the alloys compounds: a rapid diffusion of Mg and a controlled volume expansion. New negative electrodes have therefore been studied by exploring the synergy between different elements, from simple synthesis routes to nanostructuration (laser pyrolysis, chemical reduction…). A particular effort was subsequently brought on the in-depth understanding of the reaction mechanisms between these alloys and Mg and of the surface reactions with the electrolyte. The fundamental understanding of the magnesiation/demagnesiation processes required coupled electrochemical, structural and spectroscopic characterizations performed ex situ, in situ and operando. Finally, we examined the formulation of the composite electrodes through the influence of the polymer binder and the composition of the electrodes on the electrochemical performance.

Through this methodology, we identified two promising materials: InSb and In-Pb. The combination of Sb with In in InSb partially unlocked the electrochemical activity of Sb towards Mg, demonstrated for the first time in the literature. We revealed in these two new materials a competition between amorphization and crystallization of the phases formed during the reaction with Mg. The nanostructuration also has an influence on these mechanisms, but has little effect on the performance of InSb. These results demonstrate the value of fundamental research on Mg batteries.

Through this project, we have demonstrated that InSb is a promising material, opening interesting prospects not only for Mg batteries, but also for sodium-ion batteries. Better performance is obtained with nanostructured InSb than with its Sb parent, which has never been demonstrated in the literature. Finally, these alloy materials for Mg batteries are compatible with standard electrolytes, which offers the possibility of coupling them with high voltage cathodes, and to determine the real interest of Mg batteries in the panel of existing technologies.

Through conferences communications and publication of scientific articles in peer-reviewed journals, the interest in alloys as negative electrodes of Mg batteries has been further reflected in the literature. The availability of the results from the MAGICIEN project opens the way for future research on this topics and on its associated issues (characterization, formulation, etc.).

The emergence of electric vehicles and renewable energy storage to reduce our impact on environment and overcome the future shortage of petroleum, highlights the need of fundamental research to increase the energy density of batteries while decreasing cost and enhancing safety. The JCJC project MAGICIEN proposes the exploration of an innovative concept for energy storage: magnesium (Mg)-ion batteries. Magnesium appears as a great alternative to lithium due to its high capacity, low cost, abundance on Earth and largely smaller reactivity and better safety compared to lithium. While the use of magnesium metal at the negative electrode of Mg batteries promises great capacity, there is not yet electrolyte solutions that can be compatible with both magnesium metal at low potential and positive electrodes at high potentials. Conventional electrolytes used in Li batteries strongly interact with magnesium metal to form a barrier on the surface of the Mg metal, inhibiting reversible electrochemical reactions in the cell. An innovative concept to solve this issue is to replace the negative Mg metal electrode with a material compatible with solvents and electrolyte solutions with wider electrochemical stability windows. Mg alloys compounds, analogous to the Li alloys negative electrodes, possess adequate stability in conventional electrolytes and slightly higher potentials than pure Mg metal. Their capacity is smaller than pure Mg, yet still sufficient to provide a substantial increase of the capacity of batteries when combined with a high capacity positive electrode. In this project, the innovative approach is to elaborate high capacity and efficient negative electrodes, based on nanostructured intermetallic alloys or pnictides compounds. The first objective is the synthesis of unexplored nanostructured binary or ternary alloys or pnictides offering higher cycling performance (capacity, coulombic efficiency) than state-of-art materials. The nanostructuration will be beneficial to develop highly efficient negative electrodes for Mg-ion batteries, mitigating the large volume changes predicted upon full magnesiation and enhancing the sluggish diffusion of Mg2+ ions in the solid-state. An important goal of the project is to achieve a strong understanding of the magnesiation/demagnesiation reaction mechanisms of the unexplored compounds. A particular attention will also be paid on the reactivity at the interface of the electrode with the electrolyte. We aim at investigate the underlying mechanisms responsible for the different reactivity of the alloys towards conventional electrolytes compared to Mg metal. Finally, the last objective is the elaboration of effective cells with optimized electrode and electrolyte’s formulations to achieve highly enhanced performance. Acquired knowledge in the project will be of great help at designing stable, efficient and low-cost post-Li batteries.