It was recalled that graphite formed intercalates with a variety of elements and molecules because of the absence of chemical bonding between the hexagonal layer planes. The formation of a stage-one intercalate LiC6 increased the interlayer distance from 0.335 to 0.371nm. Although the diffusion of Li into graphite preceded intercalate formation, no data existed for Li transport at low Li concentrations. The release kinetics of Li from highly oriented pyrolytic graphite at Li concentrations between 1 and 10ppm were measured at 1000 to 1300K, and diffusion coefficients for the isotopes 7Li and 6Li were determined (figure 13). The Li transport in highly oriented pyrolytic graphite was strongly anisotropic, and the contribution to the total release of the diffusion perpendicular to the graphite planes was negligible. The Li diffusivity in the direction of the graphite planes was described by:

D (cm2/s) = 3 x 103exp[-1.83(eV)/kT]

The D value at 1070K was 7.6 x 10-6cm2/s.

Diffusion of Lithium in Highly Oriented Pyrolytic Graphite at Low Concentrations and High Temperatures. Jungblut, B., Hoinkis, E.: Physical Review B, 1989, 40[16], 10810-5