Lithium K(1s) synchrotron NEXAFS spectra of lithium-ion battery cathode, anode and electrolyte materials

The lithium(1s) K-edge X-ray absorption spectra of lithium-ion battery relevant materials (Li metal, Li3N, LiPF6, LiC6, and LiMn1.90Ni0.10O4) are presented. The Li and LiC6 spectra are discussed and compared with literature data. The Li in lithium-intercalated carbon LiC6, typically used as anode battery electrode material, could be clearly identified in the spectrum, and a presumed purely metallic character of the Li can be ruled out based on the chemical shift observed. The Li in corresponding cathode electrode materials, LiMn1.90Ni0.10O4, could be detected with near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, but the strong (self-) absorption of the spinel lattice provides an obstacle for quantitative analysis. Owing to its ionic bonding, the spectrum of the electrolyte salt LiPF6 contains a sharp π-resonance at 61.8 eV, suggesting a distinct charge transfer between Li and the hexafluorophosphate anion. In addition, LiPF6 resembles many spectral features of LiF, making it difficult to discriminate both from each other.Residual electrolyte on anodes or cathodes poses a problem for the spectroscopic analysis of the electrodes, because its Li spectrum overshadows the spectral features of the Li in the anode or cathode. The electrolyte must be removed from electrodes prior to spectroscopic analysis.