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.

Remarkable electrochemical and ion-transport characteristics of magnesium-fluorinated alkoxyaluminate–diglyme electrolytes for magnesium batteries

“…0.8 mol dm À3 . 47 For lithium salts consisting of highly bulky fluorinated alkoxy-or arylaluminate anions such as Al(HFIP) 4 and Al(HFTB) 4 (HFTB = hexafluoro-tertbutoxy), the G1-solution maxima reportedly appeared in the range ca. 0.5-0.6 mol dm À3 .…”

Lithium Borate Ester Salts for Electrolyte Application in Next‐Generation High Voltage Lithium Batteries

“…also calculated [BTfe] − anion to have a low HOMO (−2.763 eV) and a high HOMO‐LUMO gap. [ 20 ] Thus it is anticipated that the higher degree of fluorination in both [BHFip] − and [BTfe] − will be suitable for operation with high‐voltage cathodes for Li metal batteries.…”

Boosting High-Performance in Lithium–Sulfur Batteries via Dilute Electrolyte

“…44 In addition, 0.2 mol L -1 solution of novel salt Li[B(OTfe) 4 ] in standard solvents (DME/DOL) has been investigated in Li-S cells. 45 Since 2013, ultra-saturated salt-solvent mixtures have become a popular avenue to combat the polysulfide dissolution due to smaller fraction of solvent molecules not participating in Li + and TFSIsolvation and available for solvating the polysulfides. [46][47][48][49] However, such electrolytes typically display high viscosity, low Li + mobility, poor wetting on S cathodes, resulting in low capacity utilization, low rate capability and reduced practically attainable energy density, particularly for low E/S ratio and high mass loading cathodes.…”