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ACS Appl Mater Interfaces. 2019 Oct 2;11(39):35770-35776. doi: 10.1021/acsami.9b12709. Epub 2019 Sep 20.

Optimized Nonflammable Concentrated Electrolytes by Introducing a Low-Dielectric Diluent.

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Department of Chemical System Engineering , The University of Tokyo , 7-3-1, Hongo , Bunkyo-ku, Tokyo 113-8656 , Japan.
Elements Strategy Initiative for Catalysts & Batteries (ESICB) , Kyoto University , 1-30, Goryo-Ohara , Nishikyo-ku, Kyoto 615-8245 , Japan.


Concentrated electrolytes of LiN(SO2F)2 (LiFSA) and organic phosphates (e.g., trimethyl phosphate, TMP) are receiving intense attention for safe and long-lasting lithium-ion batteries, because of their nonflammable character and unusual passivation ability toward negative electrodes. However, their high viscosity and low ionic conductivity have hampered their practical application. In this work, a low-dielectric diluent, 1,1,2,2-tetrafluoroethyl 2,2,3,3,-tetrafluoropropyl ether (HFE), is introduced into concentrated LiFSA/TMP electrolytes. Upon dilution, the viscosity drastically decreases to 11.0 mPa s and the ionic conductivity slightly increases to 0.87 mS cm-1. More importantly, both of the nonflammable character and the unusual passivation ability are retained even after dilution. A spectroscopic analysis shows that the diluted LiFSA/TMP:HFE has a local coordination state similar to that in the concentrated LiFSA/TMP, which leads to the formation of a FSA anion-derived inorganic surface film. This work suggests the importance of the peculiar local coordination state in designing safe battery electrolytes with better passivation ability.


coordination; dilution; lithium-ion batteries; nonflammable electrolytes; passivation


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