LiTFSI-CsTFSI

In the present study, electrodeposition of Mg was investigated in a eutectic LiTFSI-CsTFSI melt at 150-200 °C. The eutectic LiTFSI-CsTFSI (0.07/0.93, mole fraction) possesses a low melting point of 112°C and good ionic conductivity (18.4mScm at 150°C) [18]. As magnesium ion sources, we tested Mg(CF3S03)2, MgCl2, and Mg(TFSI)2. 

CsTFSI was prepared by neutralization of an ethanol solution of HTFSI (Morita Chemical Industries Co., Ltd, purity > 99%) with cesium carbonate (Aldrich purity > 99.5%) and then dried under vacuum for three days at 115 °C. Mg(TFSI)2 was prepared by neutralization of an ethanol solution of HTFSI with magnesium carbonate (Wako Pure Chemical Industries, Ltd. purity > 99%) and then dried under vacuum for three days at 215 °C. Other chemicals were commercially available and used after appropriate drying treatments. The electrolyte was prepared by mixing LiTFSI (Morita Chemical Industries Co., Ltd purity > 99%) and CsTFSI in a eutectic composition (LiTFSI CsTFSI = 0.07 0.93/mole fraction) in an alumina crucible with high purity. A chromel-alumel thermocouple was used for temperature measurement. 

Second, 0.5 mol% of MgCl2 was added to a eutectic LiTFSI-CsTFSI melt at 150 °C. As shown in Figure 5.4.1c, an apparent change was not observed in the CVs for a nickel electrode. Again, an XPS result for the sample prepared by the electrolysis did not indicate the presence of Mg metal. Thus, it is difficult to... 

Figure 5.4.1 Cyclic voltammograms in eutectic LiTFSI-CsTFSI melts at 150°C. Magnesium ion sources and electrode materials are (a) Mg(CFjSOj)2 (0.5 mol%) and an Ag plate, (b) Mg(CF2602)2 (0.5 mol%) and a Ni plate, and (c) MgClj (0.5mol%) and a Ni plate. Scan rate 50mVs F The arrows indicate the direction of potential scan...

Figure 5.4.2 Cyclic voltammograms for a nickel electrode in LiTFSI-CsTFSI before and after adding 1 mol% of Mg(TFSI)2 at I50°C. Scan rate 50mVs ...

Figure 5.4.4 An Mg 2p XPS spectrum of the deposit on a Ni electrode prepared by potentiostatic electrolysis at 0.25 V versus LC/Li for I h in LiTFSI-CsTFSI-Mg(TFSI)2 (2mol% added) melt at 200°C. Argon ion etching time 720 s...

Metallic magnesium was successfully deposited by potentiostatic electrolysis in a LiTFSI-CsTFSI eutectic melt containing Mg(TFSI)2 (2 mol% added) at 200 C. The combination of a Mg(TFSI)2 ion source and an elevation of temperature is preferable for magnesium deposition in a LiTFSI-CsTFSI eutectic melt. 

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