Measurement of Tortuosity and Porosity of Porous Battery Electrodes

This paper reports methods to measure porosity and tortuosity of Li-ion battery electrodes. A gas transport resistance measurement method adapted from [Z. Yu, R. N. Carter, J. Power Sour., 195, 1079 (2010)] is used to characterize an electrode MacMullin number (i.e. the ratio of tortuosity and porosity). Porosity is measured independently, and the tortuosity is obtained from the measured MacMullin number. The measurements were carried out for graphite and Li-metal oxide electrodes taken from an automotive Li-ion battery. Tortuosities of 5.95 ± 0.51 at 28.5% ± 1.3% porosity and 3.74 ± 0.38 at a porosity of 21.5% ± 0.25% were measured for the graphite electrode and the Li metal oxide electrode respectively. Additionally, the tortuosity values for both electrodes were found to be significantly higher than those predicted by the Bruggeman correlation, suggesting that use of the Bruggeman correlation for Li-ion battery electrode modeling is not applicable and tortuosity should be measured for the electrodes of interest.