Raman Diagnostics of Cathode Materials for Li-Ion Batteries Using Multi-Wavelength Excitation

Abstract

Lithium-ion batteries have been commonly employed as power sources in portable devices and are of great interest for large-scale energy storage. To further enhance the fundamental understanding of the electrode structure, we report on the use of multi-wavelength Raman spectroscopy for the detailed characterization of layered cathode materials for Li-ion batteries (LiCoO2, LiNix Co1−x O2, LiNi1/3 Mn1/3 Co1/3 O2 ). Varying the laser excitation from the UV to the visible (257, 385, 515, 633 nm) reveals wavelength-dependent changes in the vibrational profile and overtone/combination bands, originating from resonance effects in LiCoO2 . In mixed oxides, the influence of resonance effects on the vibrational profile is preserved but mitigated by the presence of Ni and/or Mn, highlight-ing the influence of resonance Raman spectroscopy on electronic structure changes. The use of UV laser excitation (257, 385 nm) is shown to lead to a higher scattering efficiency towards Ni in LiNi1/3 Mn1/3 Co1/3 O2 compared to visible wavelengths, while deep UV excitation at 257 nm allows for the sensitive detection of surface species and/or precursor species reminiscent of the synthesis. Our results demonstrate the potential of multi-wavelength Raman spectroscopy for the detailed characterization of cathode materials for lithium-ion batteries, including phase/impurity identification and quantification, as well as electronic structure analysis.