Boron esters as tunable anion carriers for non-aqueous batteries electrochemistry

Compounds like LiF, Li2O, and Li2O2 have considerable importance in batteries; the first two are ubiquitous in the protective SEI at the negative electrode, or the result of conversion reactions with fluorides and oxides. The latter, Li2O2, forms from oxygen reduction in the much vaunted Li/air batteries. Mastering their solubility in Li-based electrolytes is viewed as essential for further progress in battery safety, lifetime, or capacity. Aprotic solvents cannot provide the H-bonds necessary to their dissolution, and simple practical solutions have yet to materialize. Here we disclose a novel and large family of boron esters of general formula Y-C((CH2O)(Z1O)(Z2O))B whose Lewis acidity stems from geometrical constraint and can be tuned via electron affinity either by Y = CH3 → Y = NO2 or Z 1,2 ) CH2 → Z1,2 ) CO so as to partially or fully dissolve the above compounds both in battery solvent EC/DMC and in DMF. The extreme simplicity of synthesis and variability of these boron-based anion carriers, where the exchange rate is fast, are not only a valuable addition to coordination science but also a step forward to improve present battery systems. © 2010 American Chemical Society