Electrolytes Beyond the State of the Art for Rechargeable Magnesium Batteries

Recently, rechargeable magnesium batteries have been attracting an increased attention as a candidate for a post Li-ion battery owing to a high volumetric capacity (3833 mAh cm^-3 vs. 2046 mAh mAh cm^-3  for Li) , absence of dendrites formation and the lower cost of Mg metal (about 10 times cheaper than Li).  Nonetheless, current Mg battery technologies suffer from several drawbacks which hamper reaching its full potential.  For example, the absence of robust and practical high voltage/high capacity cathodes currently limits the energy density which could be harnessed using these batteries.^[1]  Another major challenge relates to the electrolytes used in magnesium batteries. Current state of the art electrolytes use Grignard/organohalo magnesium reagents and complexes since electrolytes based on conventional inorganic and ionic Mg salts were found to passivate the Mg metal surface. ^[1] These organohalo reagents, while possessing an impressive electrochemical performance, were found to cause corrosion to the metallic battery parts such as current collectors.  This corrosive nature has been linked to the presence of the chloride ion which is an integral part of the electrolytes’ make.  Therefore, a new strategy for designing electrolytes for magnesium batteries is highly desired. We have been pioneering the development of a new class of electrolytes that are based on borohydrides salts.  These represent the first and only example of an inorganic, relatively ionic and halide free salts reported to date that are compatible with Mg metal. ^[2] These electrolytes were used in the first rechargeable Mg battery utilizing an inorganic salt leading to opening a new dimension in the design space of magnesium battery electrolytes.  Here, we will explain our design strategies, discuss fundamental properties obtained from systematic spectroscopic and electrochemical studies and share up-to-date results related to these new promising systems.

 References

[1] H. D. Yoo, I. Shterenberg, Y. Gofer, G. Gershinsky, N. Pour, D. Aurbach, Energy Environ. Sci. 2013, 6, 2265-2279.

[2] R. Mohtadi, M. Matsui, T. S. Arthur, S.-J. Hwang, Angew. Chem. Int. Ed. 2012, 51, 9780 –9783.