Electrochemical stability of lithium salicylato-borates as electrolyte additives in Li-ion batteries

A systematic study has been performed for several chelato-borate complexes by combining electrochemical characterization and ab-initio calculations to reveal whether they are appropriate to be used as electrolyte components in Li-ion batteries. The chelato-borates used in this study are lithium bis(oxalato) borate (LiBOB), lithium salicylatooxalatoborate (LiSOB), lithium bis(salicylato)borate (LiBSB), lithium bis(3-methylsalicylato)borate, lithium bis(5-fluorosalicylato)borate, lithium bis(5-chlorosalicylato) borate, lithium bis(5-bromosalicylato)borate, and lithium bis(3,5-dichlorosalicylato)borate. A graphite electrode is chosen to study the cathodic stability, while LiMn2O4 is selected to estimate the anodic stability limits of these chelato-borates. Additionally, the oxidation potentials of these compounds are predicted by employing density functional theory (DFT) calculations. The CV studies of graphite electrodes in these electrolyte mixtures indicate that irreversible reduction of the oxalato and salicylato groups occurs at 1.6-1.8 and 0.9-1.3 V vs. Li/Li+, respectively. Besides, irreversible oxidation of the bis(salicylato)borate anions between 4.3 and 4.8 V vs. Li/Li+ is observed in the CV curves of LiMn2O4 electrodes, depending on the respective ligands around the central boron atom. The theoretical calculations are generally in line with the experimental observations. Furthermore, they help to explain the differences between the oxidation potentials of the anions, which are caused by the different groups that donate the electron and the respective substitution pattern. (C) 2013 Elsevier B.V. All rights reserved.