Li[B(OCH2CF3)4]: Synthesis,Characterization and Electrochemical Application as a Conducting Salt for LiSB Batteries

A new Li salt with views to success in electrolytes is synthesized in excellent yields from lithium borohydride with excess 2,2,2‐trifluorethanol (HOTfe) in toluene and at least two equivalents of 1,2‐dimethoxyethane (DME). The salt LiB(OTfe)₄] is obtained in multigram scale without impurities, as long as DME is present during the reaction. It is characterized by heteronuclear magnetic resonance and vibrational spectroscopy (IR and Raman), has high thermal stability (T_{decomposition}>271 °C, DSC) and shows long‐term stability in water. The concentration‐dependent electrical conductivity of LiB(OTfe)₄] is measured in water, acetone, EC/DMC, EC/DMC/DME, ethyl acetate and THF at RT In DME (0.8 mol L ^?1) it is 3.9 mS cm^?1, which is satisfactory for the use in lithium‐sulfur batteries (LiSB). Cyclic voltammetry confirms the electrochemical stability of LiB(OTfe)₄] in a potential range of 0 to 4.8 V vs. Li/Li⁺. The performance of LiB(OTfe)₄] as conducting salt in a 0.2 mol L ^?1 solution in 1:1 wt % DME/DOL is investigated in LiSB test cells. After the 40th cycle, 86 % of the capacity remains, with a coulombic efficiency of around 97 % for each cycle. This indicates a considerable performance improvement for LiSB, if compared to the standard LiNTf₂]/DOL/DME electrolyte system.