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Electrochemical Investigation of the Solid Electrolyte Interface on Lithium Electrodes Cycled with a Glyme-Litfsi Electrolyte
In this contribution we report on the formation of the solid electrolyte interphase (SEI) on lithium electrodes in glyme (tetra ethylene glycol dimethyl ether, G4) - LiTFSI electrolytes with different molar ratios (G4:LiTFSI, 8:1 to 1:1). As the molar ratio (G4:LiTFSI) decreases the cycling efficiency, in terms of lithium deposition and dissolution on Cu disks, increases from 20% to around 95% for the 1:1 complex. The cycling behavior and impedance measurements in symmetric cells show that the electrolytes with various molar ratio of G4 to LiTFSI result in SEI films with different properties. Furthermore, the SEI film formed in the electrolyte with the equimolar ratio is relatively stable and our results indicate that the equimolar complex of G4 and LiTFSI has an improved compatibility with the lithium electrode. From X-ray photoelectron spectroscopy (XPS), with argon-ion sputtering for depth profiling, we find that the relative amount of fluorinated species, such as LiF and C-F, in the films increases with increasing molar ratio of G4 to LiTFSI. This suggests that the breakdown of TFSI anions is more likely to happen in electrolytes with higher glyme concentration. These results are of importance when considering the implementation of G4-LiTFSI complexes as electrolytes in Li-metal type batteries.
Fig. 1. Cycling efficiency (EFF) of the lithium deposition and dissolution on Cu disk in [Li(G4)x][TFSI] (x = 1, 2, 4, and 8).
Acknowledgements
The support provided by China Scholarship Council (CSC) during a visit of Shizhao Xiong to Chalmers is acknowledged. We are grateful to the support of the Areas of Advance Energy, Materials Science, and Transport at Chalmers.
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