Novel Transmetalation Reaction for Electrolyte Synthesis for Rechargeable Magnesium Batteries
Interestingly, it is found in the literature that crystallographic studies of the electrolytes generated from various combinations of organomagnesium compounds and Lewis acids reveal very similar structures, in which a cation, consisting of two magnesium atoms bridged by three chlorines, pairs with a counter anion such as an organo-aluminate or borate.5-8These results imply that such binuclear magnesium compounds are thermodynamically favored in the reaction between an organomagnesium and a Lewis acid. Moreover, these binuclear magnesium complexes are capable of reversible Mg deposition and show enhanced oxidative stability compared to the reaction mixtures.
Herein we present a novel transmetalation reaction between MgCl2and organoaluminum compounds which leads exclusively to the electrochemical active aluminate complex, as expressed in the general chemical equation 1 (x = 1, 2, 3; neglecting the solvent ligands).
2MgCl2 + RxAlCl3-x → [Mg2Cl3]+[RxAlCl4-x]- 1
Through this reaction, we are also able to obtain a chemical bond between aluminum and the ligand in the complexes which is more stable than the Al-C bonds and are thus able to optimize the properties of the electrolyte. Owing to the higher electronegativity of nitrogen and oxygen, the polar Al-N or Al-O bonds in the aluminate anion should benefit the voltage stability of the electrolyte. We have developed a straightforward synthetic route for the Al-O bond containing electrolyte by employing the transmetalation reaction. The as-prepared electrolyte shows an anodic stability of up to 3.4 V, good air-stability and ionic conductivity.
The one-step synthesis without organomagnesium compounds can serve as a useful tool to design the electrolyte composition and improve the performance of the electrolytes. The feasibility of the transmetalation reaction with various aluminium Lewis acids opens the door for the accessibility of air-stable and non-nucleophilic electrolyte for high energy magnesium batteries such as magnesium air and magnesium sulphur batteries.
1 T. D. Gregory, R. J. Hoffman and R. C. Winterton, J. Electrochem. Soc., 1990, 137, 775–780.
2 D. Aurbach, Z. Lu, A. Schechter, Y. Gofer, H. Gizbar, R. Turgeman, Y. Cohen, M. Moshkovich and E. Levi, Nature, 2000, 407, 724–727.
3 O. Mizrahi, N. Amir, E. Pollak, O. Chusid, V. Marks, H. Gottlieb, L. Larush, E. Zinigrad and D. Aurbach, J. Electrochem. Soc., 2008, 155, A103–A109.
4 Y. S. Guo, F. Zhang, J. Yang, F. F. Wang, Y. N. NuLi and S. I. Hirano, Energy Environ. Sci., 2012, 5, 9100–9106.
5 D. Aurbach, N. Pour, Y. Gofer and D. T. Major, J. Am. Chem. Soc., 2011, 133, 6270–6278.
6 H. S. Kim, T. S. Arthur, G. D. Allred, J. Zajicek, J. G. Newman, A. E. Rodnyansky, A. G. Oliver, W. C. Boggess and J. Muldoon, Nat. Commun., 2011, 2, 427.
7 Y. S. Guo, F. Zhang, J. Yang, F. F. Wang, Y. N. NuLi and S. I. Hirano, Energy Environ. Sci., 2012, 5, 9100–9106.
8 Zhirong Zhao-Karger, Xiangyu Zhao, Olaf Fuhr and Maximilian Fichtner, RSC Adv. 2013, 3, 16330–16335.