The Diffusion of Li in Poco Graphite and Glassy Carbon at Low Concentrations and High Temperatures

Abstract

Abstract X‐ray diffraction and angle dependent X‐ray absorption near edge structure (XANES) measurements were carried out in order to characterize a Poco graphite and a glassy carbon with respect to their long range and short range orders. Poco graphite is a well graphitized polycrystalline material. Glassy carbon has, by contrast, hardly any long range order, but XANES spectra reveal the graphite‐like short range order. The diffusion of 7 Li in Poco graphite and in glassy carbon was investigated at Li atomic fractions between 0.1 ppm and 300 ppm and temperatures in the range from 1000 K to 1400 K using a mass spectrometric method. Li was found to be released from Poco graphite mainly via intragranular diffusion and not by Knudsen diffusion through the open interconnected pores. The inaccessible porosity of glassy carbon is equal to the total porosity i.e. open pores are not present. The Arrhenius equations for the diffusion coefficients of Li in Poco graphite and in glassy carbon are D = 3 · 10 4 · exp(‐2.27 eV/ kT ) cm 2 /s and D = 1.5 · 10 6 · exp(‐3.1 eV/ kT ) cm 2 /s.