Synthesis, analysis, and purification of new lithium salts for lithium batteries, lithium bis[tetrafluoro-1,2-benzenediolato(2-)-O,O']borate and lithium bis[2 ,3-naphthalenediolato(2-)-O,O'}borate are described, and the results of electrochemical studies of these salts and of lithium bis[3-fluoro-1,2-benzenediolato(2-)-O,O']borate, in propylene carbonate are reported. The effect of the electron-withdrawing substituent fluorine results in an increase of the electrochemical window by 0.1 V/fluorine per one chelate ligand. The slope, which can be calculated from the linear correlation of the highest occupied molecular orbital energies with anodic oxidation potentials is -3.0 eV/V, a value equal to that known for aryl borates and fluoroaryl borates.
Disclosed is a new class of nontoxic thermally, chemically, and electrochemically stable, inexpensive lithium salts based on a chelate complex anion of boron with aromatic or aliphatic diols or carboxylic acids. The synthesis, purification, and analysis of the first member of this class, lithium bis[1,2-benzenediolato( 2-)-O,O']borate (Li[B(C6H402)_~]) is described and some results are given from electrochemical experiments of its solution in various aprotic solvents. The voltage window of Li[B(C6H402)2] based solutions is limited by the oxidation of the borate at about 3.6 V vs. lithium. Lithium can be cycled in solutions of lithium bis[1,2-benzenediolato(2-)-O,O']borate based on different aprotic solvents. Cycling efficiencies depend strongly on the solvents used, but scarcely on contact times of the solution with lithium, or on the use of mixed electrolytes (Li[B(C6H~O2)2]/[N(CH3)4] [B (C6H40_~)2]).
A conductivity study is carried out on lithium bis[1,2 benzenediolato (2-)-O,O']borate and on lithium bis[3-fluoro-1,2benzenediolato(2-)-O,O']borate in dimethoxyethane and propylene carbonate from infinite dilution to saturation in the temperature range 228 .c T (K) <308. The electron-thawing fluorine substituent produces a decrease of the association constant by a factor of about three for PC-based solutions and 5.5 for solutions in dimethoyxyethane. The increase in the maximum of conductivity by about 30% (propylene carbonate) and about 80% (dimethoxyethane), independent of temperature, reveals the effect of ion-ion interaction on the conductivity maximum, with the solvent permittivity, viscosity, and ionic radii remaining unchanged. Synthesis, analysis, and purification of lithium bis[3-fluoro-1,2-benzenediolato(2-)O,O'Jborate, which is a candidate for lithium batteries, is described.
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