Polymeric Gel Electrolyte Based on a Rotaxane-Networked Polymer with Alkyl Magnesium Bromide and Ionic Liquid for Rechargeable Mg Batteries

Wednesday, 8 October 2014
Expo Center, 1st Floor, Center and Right Foyers (Moon Palace Resort)
N. Yoshimoto, K. Yamabuki, I. Kim, R. Shigematsu (Graduate School of Science and Engineering, Yamaguchi University), and H. Tsutsumi (Graduate School of Medicine, Yamaguchi University)
Rechargeable magnesium (Mg) battery that uses metal Mg as the negative electrode is a potential candidate of the next-generation power sources for electric vehicles (EV) and other large scale applications.  We previously reported that Mg is reversibly deposited and dissolved on a metal substrate in mixed solutions containing ionic liquid and alkyl magnesium bromide [1].  However, as the electrolyte system contains high vapor pressure THF, the resulting battery will have still practical problems in safety and reliability.  Recently, we have synthesized a novel network polymer with a rotaxane structure, a complex consisting of secondary ammonium salt and 24-membered crown ether component [2].  In this study, a novel gel electrolyte based on a rotaxane-networked polymer has been prepared, in which ethyl magnesium bromide dissolved in triethylene glycol dimethyl ether (C2H5MgBr/Triglyme) and N,N-diethyl-N-methyl- N-(2-methoxyethyl)ammonium bis(trifluoromethylsulfonyl) imide (DEMETFSI) were included.  The ionic conductance behavior and electrochemical behavior of the resulting gel electrolytes were investigated.
A “rotaxane network” was synthesized in the same manner as our previous report [2] (Fig.1).  The gel electrolytes were prepared by an impregnation method: the polymer film was immersed in the mixed solution of C2H5MgBr/Triglyme and DEMETFSI for 24 h.  The resulting network polymer maintained the stable shape without decomposing after a month’s impregnation in 1M C2H5MgBr/Triglyme. 
The “rotaxane network” polymeric gel electrolyte impregnated in C2H5MgBr/ Triglyme + DEMETFSI exhibited an ionic conductivity of 2.8×10-4 S cm-1 at 20°C (swelling degree = ca. 60%).  Highly reversible behavior was observed for cathodic deposition and anodic dissolution of Mg in this polymeric gel electrolyte system.
This research was financially supported by the Japan Science and Technology Agency (JST), Advanced Low Carbon Technology Research and Development Program (ALCA).

[1] N. Yoshimoto, M. Matsumoto, M. Egashira, and M. Morita, J. Power Sources, 195, 2096(2010).
[2]  K. Yamabuki, K. Onimura, and T. Oishi, Polymer Journal, 40, 205(2008).