Li-ion Diffusion in Porous Carbon Electrode Materials by GITT Method

The process of diffusion of lithium ions into porous carbon electrode materials obtained by hydrothermal carbonization of plant raw materials at different temperatures was the galvanostatic intermittent titration technique. The diffusion coefficient of lithium ions in the electrode material was calculated and its dependence on the intercalation degree x was analyzed. It was found that with the increase in the carbonation temperature of the raw material, which results in the removal of gaseous aliphatic and then aromatic molecules with low molecular weight, processes of cyclization and aromatization of molecules, as well as intensive carbonization of the raw material, the formation of carbon layers and primary graphite nuclei, the coefficient diffusion increases due to ordering the structure of the porous carbon material and reducing its specific surface area and total pore volume. When the maximum value of the intercalation degree is reached, the diffusion coefficient of lithium ions is 3.6·10 – 12 сm2/s (х = 0.28), 7.9·10 – 12 сm2/s (х = 0.44), and 1.9·10 – 10 сm2/s (х = 0.19) for samples obtained at carbonization temperatures of 600, 750, and 1000 °C, respectively. A comparative analysis of the values of the diffusion coefficient, calculated on the basis of the data of galvanostatic intermittent titration technique and electrochemical impedance spectroscopy, was carried out.