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Novel Mg Electrolytes for Rechargeable Mg Batteries Based on [Mg2(μ-Cl)2]2+ Cation
An attractive path to increase energy storage capacities, lower the material costs, and improve operation safety involves the use of multi-valent elements with low reduction potentials. Key benefits of multi-valent systems over mono-valent (i.e. Li, Na) include (1) Increased electrons available per molecule that significantly impacts energy density characteristics. Potential candidates include magnesium (Mg) that can lose two electrons and aluminum three electrons, coupled with increased abundance and decreased production cost makes them viable alternatives for low cost energy storage. In this presentation, a novel [Mg2(μ-Cl)2]2+ cation complex, which is highly active for reversible Mg electrodeposition, was identified for the first time in this work. This complex was found to present in electrolytes formulated in dimethoxyethane (DME) through dehalodimerization of non-nucleophilic MgCl2 by reacting with either Mg salts (such as Mg(TFSI)2, TFSI= bis(trifluoromethane)sulfonylimide) or Lewis acid salts (such as AlEtCl2 or AlCl3).The electrolyte synthesis and understandings developed in this work could be insightful for rational formulation of a family of electrolytes with the general formula [Mg2(μ-Cl)2(DME)4][anion]x, and provide new opportunities for developing cathode materials, and therefore could be significant for practical Mg batteries.