title: Li[B(OCH2CF3)4]: synthesis, characterization and electrochemical application as a conducting salt for LiSB batteries.
abstract: 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 Li[B(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 (Tdecomposition >271 °C, DSC) and shows long-term stability in water. The concentration-dependent electrical conductivity of Li[B(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 Li[B(OTfe)4 ] in a potential range of 0 to 4.8 V vs. Li/Li(+) . The performance of Li[B(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 Li[NTf2 ]/DOL/DME electrolyte system.
authors.affiliation: Institut für Anorganische und Analytische Chemie and Freiburger Materialforschungszentrum (FMF), Universität Freiburg, Albertstr. 21, 79104 Freiburg (Germany).
authors.forename: Michael
authors.initials: M
authors.lastname: Rohde
authors.forename: Philipp
authors.initials: P
authors.lastname: Eiden
authors.forename: Verena
authors.initials: V
authors.lastname: Leppert
authors.forename: Michael
authors.initials: M
authors.lastname: Schmidt
authors.forename: Arnd
authors.initials: A
authors.lastname: Garsuch
authors.forename: Guenter
authors.initials: G
authors.lastname: Semrau
authors.forename: Ingo
authors.initials: I
authors.lastname: Krossing
keywords: electrolytes; lithium-ion batteries; lithium-sulfur batteries; vibrational spectroscopy; weakly coordinating anions