LiBOB and its derivatives - Weakly coordinating anions, and the exceptional conductivity of their nonaqueous solutions

We describe the synthesis and properties of a new class of lithium salts in which the anions are dicarboxylic acid derivatives of orthoborate. The sin gle negative charge of these anions is shared by eight oxygen atoms (more a ccurately four oxygen atoms and four carbonyl groups), hence it is very spr ead out, and the coordinating ability of the anions is consequently very we ak. Judged by comparison of the high-temperature conductivities of 0.5 M li thium salt solutions with those of other weakly basic anions in a low diele ctric constant solvent 1,2-dimethoxyethane, the first member of the new fam ily, lithium bis(oxalato) borate, LiBOB, is dissociated much more than are LiClO4 or LiCF3SO3 and even more than lithium bis(trifluoromethane) sulfony limide, LiTFSI. Conductivities of solutions in acetonitrile approach those of aqueous solutions. Solutions of LiBOB in propylene carbonate have high e lectrochemical stabilities, up to similar to4.5 V vs. Li+/Li. Higher member s of the series exhibit lower solubilities, but are also highly dissociated in dilute solution. (C) 2000 The Electrochemical Society. S1099-0062(00)08 -093-7. All rights reserved.