A Raman spectroscopy investigation of the interactions of LiBOB with γ-BL as electrolyte for advanced lithium batteries

LiBOB (lithium bis(oxalato)-borate) based electrolytes for high power Li-ion batteries are prepared by dissolving different concentrations of LiBOB into two different types of liquid solvents, γ-Butyrolactone (γ-BL) and propylene carbonate (PC). The ionic conductivity, solubility, and viscosity of the as-prepared electrolytes are characterized and compared. Raman spectroscopic and 13C nuclear magnetic resonance spectroscopy (NMR) are employed to investigate the fundamental solvation interactions of the LiBOB with the two types of solvents. The results indicate that lithium cation tends to coordinate with the carbonyl functional group of γ-BL. In contrast, it exists mainly through ion-pairing in PC solvent. By fitting the Raman spectra, the solvation numbers for both electrolytes are calculated and compared, which would further help understand the observed difference in ionic conductivity shown by these two electrolytes.