Battery systems with low cost, high energy density, safe operation and long cycling life time have been sought after as viable technologies for storing sustainable energy and to meet increasing demands of powering portable devices and electric vehicles.  Recently, Magnesium (Mg) batteries have attracted increasing attention as a promising high energy density battery technology and alternative to lithium-based batteries for grid scale energy storage, portable devices, and transportation applications.

Magnesium as an anode material is relatively safe to use without jeopardous dendrite formation. It is earth abundant, relatively low in cost, and has a high volumetric capacity due to the divalent nature of the Mg2+ redox couple. However, the lack of practical, high-performance Mg2+ electrolytes has been a primary technical hurdle to the development of practical Mg2+ batteries. The current methods for preparing Mg2+ electrolytes involve the use of nucleophilic sources and/or Grignard reagents.

However, these nucleophilic sources and Grignard reagents are highly reactive and employing them for synthesis of Mg2+ electrolytes is complex and can result in low yields. Furthermore, their presence can limit oxidation stability of the Mg electrolyte. Also, the highly reactive chemicals can have limited compatibility with electrophiles such as high capacity cathodes and related electrolyte additives.  A need exists for improved electrolytes for Mg-based energy systems and methods for synthesizing such electrolytes.

To meet this need, researchers at PNNL have developed   technology to form electrolytes for Mg-based energy storage devices from non-nucleophilic Mg2+ sources to provide outstanding electrochemical performance and improved electrophilic susceptibility compared to electrolytes employing nucleophilic sources. The electrolytes are characterized by high oxidation stability (up to 3.4 V vs Mg), improved electrophile compatibility and electrochemical reversibility (up to 100% coulombic efficiency). Synthesis of the Mg2+ electrolytes utilizes inexpensive and safe magnesium dihalides as non-nucleophilic Mg2+ sources in combination with Lewis acids, MRaX3-a (for 3 ≥ a ≥ 1). Furthermore, addition of free-halide-anion donors can improve the coulombic efficiency of Mg electrolytes from nucleophilic or non-nucleophilic Mg2+ sources.