Still looking for a replacement for lithium? How about magnesium? Itâ€™s divalent, so it can displace double the charge per ion (i.e., Mg2+ rather than Li+). Itâ€™s much more abundant than lithium, and more stable. However, researchers investigating Mg-ion batteries have run into several limitations, including anode/electrolyte incompatibility.
Now a team at the Toyota Research Institute of North America (TRINA) has reported a major advance in the the development of electrolytes for magnesium (Mg) batteries.
In â€œAn Efficient Halogen-Free Electrolyte for Use in Rechargeable Magnesium Batteries,â€ published in the journal Angewandte Chemie, the researchers, led by TRINAâ€™s Dr. Rana Mohtadi, describe how they developed an electrolyte based on a magnesium monocarborane salt (MMC) that is compatible with Mg metal, has high anodic stability, and is non-corrosive.
The development of a non-corrosive electrolyte enabled the first demonstration of a high-voltage coin cell battery. â€œThis achievement is a turning point in the research and development of Mg electrolytes that has deep implications for realizing practical rechargeable Mg batteries,â€ wrote the scientists.
â€œMg metal offers high volumetric capacity (3,833 mAh cm3 vs. 2,036 mAh cm3 for Li metal) while being non-dendritic and abundant in the Earthâ€™s crust. Since Aurbach et al demonstrated the first rechargeable Mg battery prototype, challenges toward realizing Mg batteries still remain. These stem from the absence of practical electrolytes and high capacity/high voltage cathodes. The field demands electrolytes capable of operating at high voltages whilst being compatible with Mg metal and all other battery components.â€
In 2014, Mohtadi and her TRINA colleagues demonstrated the effectiveness of Mg(BH4)2 as an electrolyte â€“ the first non-organomagnesium electrolyte compatible with Mg metal. Since then, the team has been seeking materials with high oxidative stability.
â€œHigh oxidative stability is crucial for the development of Mg batteries for operation with future high-voltage cathodes. Although organomagnesium compounds with oxidative stability above 3 V (vs Mg) have been reported, most have significantly reduced oxidation onset potentials when deposition and stripping occurs on non-noble-metal surfaces. Mg(BH4)2 displayed enhanced stability on these metals. We therefore sought to identify an electrolyte candidate which would retain the attractive properties of Mg(BH4)2 but offer enhanced oxidative stability.â€
Pursuing a new design concept involving boron cluster anions, the team found that monocarborane CB11H12- produced the first halogen-free, simple-type Mg salt that is compatible with Mg metal and displays an oxidative stability surpassing that of ether solvents.