Nonaqueous Lithium Battery Electrolytes Based on Bis(polyfluorodiolato)borates

Abstract

Ten lithium salts recently reported by our laboratory have been studied for their potential use as battery electrolytes. The parent compound is One derivative had a t-butyl and a methyl group on each of the two phenyl rings of the borate anion, and the other eight derivatives had one, two, or three fluorine atoms in various positions on each of the phenyl rings. Except for the t-butyl/methyl derivative, all of the borates were oxidized at potentials more positive than 4.2 vs. in 1,2-dimethoxyethane (DME) and in 50:50 mol % ethylene carbonate:dimethylcarbonate (EC:DMC). None of the anions was reduced at vs. in either solvent, and, in contrast to none caused significant corrosion of an aluminum electrode at 4.2 V vs. Except for the t-butyl/methyl derivative, the DME values occurred for 0.5 M solutions and ranged from 5.39 to The DME and EC:DMC values for were 5.88 and respectively. For a given number of phenyl-ring fluorine atoms (one, two, or three), the conductivity and the potential to passivate platinum or stainless steel electrodes depended strongly on the fluorine-atom substitution pattern. The potential at which the borate was oxidized only depended on the number of fluorine atoms and not on their substitution pattern. © 2003 The Electrochemical Society. All rights reserved.