Vibrational spectroscopy and ab initio studies of lithium bis(oxalato) borate (LiBOB) in different solvents

The effect of lithium ion coordination with the bis(oxalato) borate (BOB-) [B(C2O4)(2)](-) anion in DMSO, PEG, PPG, and d-PPG has been studied in detail by IR and Raman spectroscopy. Ab initio calculations were performed to allow a consistent analysis of the experimental data. The main features observed in the IR and Raman spectra correspond to the presence of "free", un-coordinated, BOB- anions. Only with use of d-PPG as solvent a small amount of Li+center dot center dot center dot BOB- ion pairs were detected. The Raman spectra and the calculations together indicate that Li+ coordinates bidentately with two end-oxygen atoms of the BOB- anion. The identification of ion pairs can be used to reveal limitations of LiBOB based electrolytes. The results for LiBOB are compared with literature on other Li salts.