13C NMR Study of the Electronic Structure of Lithiated Graphite

Abstract

The change in the electronic structure of graphite during electrochemical lithiation was investigated using solid-state NMR. The 13C NMR peak positions for the lithiated graphite compounds stages 3L - 1 were assigned. The dense stage LiC12 and LiC6 compounds were shown via 13C and 7Li to be metallic in nature, with Korringa relaxation being the dominant relaxation mechanism for both nuclei. The 7Li NMR shifts in graphite can be described by a direct Fermi-contact Knight shift, while the 13C NMR shifts can be described by the spin-dipolar Knight shift and isotropic Knight shift. The isotropic 13C NMR Knight shift of LiC6 was smaller than expected for a Knight shift caused purely by the core polarisation of 1s-orbitals. This showed that there must be a contribution of 2s-orbitals at the Fermi level. The density of states at the Fermi level, ρ (EF ), for LiC6 was estimated and the values, which are dependent on the Stoner enhancement factor, α, agree reasonably well with those found in literature.