Plating/Stripping Performance of Different Substrates in Magnesium Borohydride Solution

Plating/Stripping Performance of Different Substrates in Magnesium Borohydride Solution

James D. Saraidaridis¹, Gulin Vardar², Alice E. S. Sleightholme¹, Donald J. Siegel³, Charles W. Monroe¹

¹Department of Chemical Engineering, University of Michigan

²Department of Materials Science and Engineering, University of Michigan

³Department of Mechanical Engineering, University of Michigan

2300 Hayward St

Ann Arbor, MI 48109

High theoretical energy densities have attracted many researchers to metal-oxygen batteries in search of post-Li-ion technologies. The Mg-O₂ chemistry offers higher theoretical volumetric energy densities than popular Li-O₂ chemistry [1][2], which is important in constrained-volume applications like electric vehicles.  A magnesium system has large potentials associated with oxygen reactions forming MgO (2.95V vs. Mg/Mg²⁺) and MgO₂ (2.91V vs. Mg/Mg²⁺). The largest hurdle to demonstrating rechargeable Mg-O₂ batteries remains the development of suitable electrolytes that allow plating/stripping of Mg metal, prevent side reactions at potentials dictated by the plating and oxygen reactions, and are chemically inert to O₂.

Researchers recently demonstrated the use of magnesium borohydride (Mg(BH₄)₂) in DME as an electrolyte in a Mg-ion battery [3]. We sought to explore the performance of this electrolyte with various electrode substrates. The use of microelectrodes and a consistent dimensionless scan rate allows a fair comparison between electrodes of different material and radii. While no substrate was found stable across the relevant potentials for Mg-O₂ reaction, there is a clearly demonstrated difference in the substrate activity for the Mg plating/stripping reaction.

[1] C. Zu, H. Li. (2011). Energy & Environmental Science. 4: 2614-2624.

[2] K. Abraham, Z. Jiang. J. Electrochem. Soc. 143: 1-5.

[3] Mohtadi, M. Matsui, T. Arthur, S. Hwang. Angewandte Chemie. 51: 9780-9783.