Important Aspects for Reliable Electrochemical Impedance Spectroscopy Measurements of Li-Ion Battery Electrodes

To obtain the true electrochemical impedance spectrum of a Li-ion battery electrode at different stages of cycling is delicate. Measurement in a 3-electrode setup, to deconvolute the impedance of the working electrode (WE) from the counter electrode (CE), is sensitive to the cell geometry and electrode arrangement, and can lead to artefacts like distortions, induction loops and scaling effects of the spectra. Furthermore, using a CE with higher impedance than the WE also hugely alters the impedance response of the WE. There is little awareness in the field of Li-ion batteries of the occurrence of such impedance spectra falsifications, which are therefore often disregarded. Here, some of the artefacts are experimentally dismantled. Two cell designs for cycling battery electrodes with intermittent impedance measurement are presented and compared. The reusable cells are built for ring electrodes aligned concentrically with a reference electrode (RE) in the center. The reliability of the impedance response measured in these cells is confirmed in a symmetric electrode setup. It is further shown that the cells support lithiation and delithiation behavior conform with established 2-electrode cells.