Impedance Spectroscopic Studies of the Porous Structure of Electrodes containing Graphite Materials with Different Particle Size and Shape

The porous structure of graphite electrodes was studied by applying impedance spectroscopy methods to symmetric cells. The electrode structure was varied by changing the particle size distribution and particle shape of the graphite powders used to prepare the electrodes. In addition electrode parameters such as electrode loading, thickness, and density were varied in order identify their effect on the porous structure. A clear correlation between the equivalent distributed resistance of the symmetric graphite cells and the porosity of an electrode was identified which is independent from the electrode parameters. This correlation is typical for a given graphite type. It was, however, possible to identify a clear trend with the graphite powder particle size distribution and particle shape. These findings suggest a correlation of the equivalent distributed resistance with the tortuosity of the graphite electrodes. In the case of flaky graphite materials the equivalent distributed resistance increases dramatically with the increase in electrode compaction causing a high tortuosity of the electrode. In the case of bulky or round-shaped graphite materials the equivalent distributed resistance is not much affected by the densification of the electrode which could be explained by smaller electrode tortuosity even at higher electrode density. (C) 2016 Published by Elsevier Ltd.