Achieving Consistent Diffusivity Measurement between GITT and EIS

Accurate measurement of lithium diffusivity in electrode particles is essential for analyzing and predicting the performance of Li-ion batteries. There are two most widely used techniques: Galvanostatic Intermittent Titration Technique (GITT) and Electrochemical Impedance Spectroscopy (EIS). For GITT, a direct current (DC) pulse is applied to the cell. For EIS, the cell is connected to an alternating current (AC) source. The responses of the batteries are used to calculate diffusivity. GITT and EIS, despite different techniques, measure the same material property and are supposed to yield identical results. However, what has puzzled the community for a long time is that these two techniques often give an order of magnitude difference in the results. Our research aims to resolve this large discrepancy between these two techniques. By analyzing the diffusion profile and approximation error for various particle geometries, we show that these two techniques are consistent only when the current excitation does not impact deep inside the particles, which corresponds to the condition of short pulse time for GITT or high frequency for EIS. GITT does not depend on particle size by its assumption while EIS does. Thus, we propose an innovative approach to use EIS to determine diffusivity accurately independent of particle size or geometry. We further demonstrate experimentally that the two techniques yield identical results under the right measurement conditions. This work may provide insight on the scattering of measured diffusivity data in literature. Figure 1