X-ray Raman spectroscopy of lithium-ion battery electrolyte solutions in a flow cell

Abstract

The effects of varying LiPF6salt concentration and the presence of lithium bis(oxalate)borate additive on the electronic structure of commonly used lithium-ion battery electrolyte solvents (ethylene carbonate–dimethyl carbonate and propylene carbonate) have been investigated. X-ray Raman scattering spectroscopy (a non-resonant inelastic X-ray scattering method) was utilized together with a closed-circle flow cell. Carbon and oxygenK-edges provide characteristic information on the electronic structure of the electrolyte solutions, which are sensitive to local chemistry. Higher Li+ion concentration in the solvent manifests itself as a blue-shift of both the π* feature in the carbon edge and the carbonyl π* feature in the oxygen edge. While these oxygenK-edge results agree with previous soft X-ray absorption studies on LiBF4salt concentration in propylene carbonate, carbonK-edge spectra reveal a shift in energy, which can be explained with differing ionic conductivities of the electrolyte solutions.