A Study of Current Collectors for Magnesium Batteries in Mg(AlCl2EtBu)2/THF Electrolyte Using the Scanning Vibrating Electrode Technique

Magnesium-based secondary batteries provide a non-toxic, earth-abundant alternative to the Li-ion systems for stationary applications. The appeal of such systems has been recognised after a volumetric capacity that outperforms that of Li-ion systems was demonstrated (3833 mA h/cc compared to 2046 mA h/cc)¹. In any battery system, the compatibility of the current collector and the electrolyte is of high importance and for achieving good reversibility in rechargeable systems and a long cycle life. Aurbach et al demonstrated the reversible deposition and dissolution of the Grignard reagent, a tetrahydrofuran (THF) solution of magnesium organohalo-aluminate salt (Mg(AlCl₂EtBu)₂/THF), with a columbic efficiency of ∼100%². This electrolyte has been vastly studied since its identification and, subsequently, increased the level of interest in reversible Mg batteries.

The instability of a range of current collectors, when exposed to Grignard reagents, with the exception of Nickel, has been highlighted previously³. In the current study the scanning vibrating electrode technique (SVET) is used to map the current density over the surface of a selection of metals when polarised to an applied potential. The technique can then be used to spatially resolve anodic and cathodic activity. SVET has been used extensively in corrosion research where a wealth of literature is available. Figure 1 shows a typical SVET-derived current density surface map, obtained by scanning a metallic surface when fully immersed in electrolyte; the red peaks denote the anodic regions. The aim of the current study is to further understand the instability of certain metals, that are often considered as suitable current-collectors in Mg-based battery systems, when exposed to (Mg(AlCl₂EtBu)₂/THF). Copper, nickel, stainless steel and silver will be studied.

Figure 1 A typical SVET-derived current density surface map obtained by scanning a metallic surface when fully immersed in electrolyte.

References

1         P. Saha, M. K. Datta, O. I. Velikokhatnyi, A. Manivannan, D. Alman, and P. N. Kumta, Prog. Mater. Sci., 2014, 66, 1–86.

2         D. Aurbach, Z. Lu, A. Schechter, Y. Gofer, H. Gizbar, R. Turgeman, Y. Cohen, M. Moshkovich, and E. Levi, Nature, 2000, 407, 724–7.

3         D. Lv, T. Xu, P. Saha, M. K. Datta, M. L. Gordin, a. Manivannan, P. N. Kumta, and D. Wang, J. Electrochem. Soc, 2012, 160, A351–A355.