Imide anions such as bis(trifluorosulfonyl)amide (TFSA^-) have been widely investigated as the most typical perfluoroanion, which forms ionic liquids (ILs) with various onium cations like dialkylimidazolium and the good electrochemical and thermal stability have been attracted attention as a unique liquid electrolyte for secondary batteries especially lithium batteries. [1] Recently, research and developments of post-lithium ion battery, so called next-generation batteries, have been intensively investigated. Especially, the use of multivalent metal as an anode like magnesium, zinc and aluminum have been attracted attention due to their high volumetric energy density. However, in many case, slow diffusion of multivalent cation in a layered oxide cathode might be one of the severe problems. The use of thermally stable and less volatile ionic liquids might be one of the promising choice to enhance the diffusion in a cathode material at enough higher temperature. However, no good magnesium redox have been observed in a conventional and typical ionic liquids containing the TFSA^- .[2] In this study, we investigated the electrochemical responses of a magnesium metal and also much cheeper alloy (AZ31B) in a various molten salt such as a conventional TFSA ionic liquids, onium chloride and alkali metal intermediate temperature molten TFSA salt to discuss the reason for the poor redox in a conventional ionic liquids and the effect of the addition of halogenide like chloride.

References

[1] H. Matsumoto, Recent Advances in Ionic Liquids for Lithium Secondary Batteries, R.T.Jow, K. Xu, O. Borodin, M. Ue, (Eds.), Electrolytes for Lithium and Lithium-Ion Batteries, Chapter 4, pp.209-225, Springer, 2014, and references therein.

[2] G. Vardar, A. E. S. Sleightholme, J. Naruse, H. Hiramatsu, D. J. Shiegel and C. W. Monroe, ACS Appl. Mater. Interfaces, 6 (2014) 18033.

Acknowledgment

This study was financially supported by ALCA-SPRING, JST, MEXT, Japan.