Tuesday, 15 May 2018: 10:00
Room 609 (Washington State Convention Center)
Recently, MgTFSI2/MgCl2 electrolyte solutions in dimethoxyethane (DME) have been shown to function as viable electrolyte solutions for secondary Mg batteries that can facilitate reversible magnesium deposition/dissolution1. MgCl2 is a crucial component in these solutions. On its own, however, it is practically insoluble in DME. Therefore, the fact that it is readily dissolved in MgTFSI2/DME solution is remarkable. Addition of MgCl2 greatly improves the electrochemical performance of MgTFSI2/DME electrolyte solutions. MgTFSI2 /DME electrolyte show large overpotential for deposition (-0.6 V vs Mg) and dissolution (1.5V vs Mg). Furthermore this electrolyte exhibit poor magnesium deposition reversibility. Adding MgCl2 to this electrolyte reduces the overpotentials for both deposition and dissolution and showed 98% columbic efficiency. Thus, identifying the species formed in MgTFSI2/MgCl2 solutions are very intriguing. In this study, we identified numerus solution species that some of them were not previously identified. We believe that the newly discovered MgxCly complexes play a crucial rule in the improved electrochemical performance of the MgTFSI2 /DME electrolyte solutions. The complexes that were identified were Mg3Cl42+ (figure 1)2, Mg2Cl22+.Furthermore we showed that the hexacoordinated nature of magnesium effectively dictate the solution structure. We showed that in THF based electrolyte Mg2Cl3+ is the dominant solution specie and we didn’t see any evidence for its existence in DME based electrolytes(. We implemented a wide variety of analytical tools, including single crystal X-ray diffraction, multinuclear NMR, and Raman spectroscopy, to elucidate the structure of these solutions. Various solution species were determined, and a suitable reaction scheme is suggested(figure 1). We believe that this type of fundamental study is essential for designing new and improved electrolyte solutions for secondary magnesium batteries.
- Shterenberg, I.; Salama, M.; Yoo, H. D.; Gofer, Y.; Park, J.-B.; Sun, Y.-K.; Aurbach, D. Evaluation of (CF3SO2) 2N−(TFSI) based electrolyte solutions for Mg batteries. J. Electrochem. Soc. 2015, 162, A7118-A7128.
- Salama, M.; Shterenberg, I.; JW Shimon, L.; Keinan-Adamsky, K.; Afri, M.; Gofer, Y.; Aurbach, D. Structural Analysis of Magnesium-Chloride Complexes in Dimethoxyethane Solutions in the Context of Mg Batteries Research. The Journal of Physical Chemistry C 2017.