Electrochemical Impedance Analysis of Lithium Insertion Electrodes Using Symmetric Cells

Electrochemical impedance spectroscopy (EIS) of lithium insertion electrodes is a powerful technique to facilitate the further development of lithium-ion batteries (LIBs) because it provides useful information on electrochemical reactions.However, EIS methodology using a three-electrode cell is yet to be established owing to the difficulty in designing the reference electrode configuration.Therefore, a symmetric-cell method has been proposed to measure the EIS of a single electrode in a two-electrode cell, and it has been actively applied to EIS measurements in recent years.EIS measurements using symmetric cells have resulted in several new discoveries and deepened our understanding of the EIS behavior of lithium insertion electrodes.In this review, we outline the progress of EIS measurements using the symmetric-cell method for lithium insertion electrodes.First, we explain the principle, fabrication method, and EIS analysis of symmetric cells.Subsequently, an equivalent-circuit model representing lithium insertion electrodes is proposed based on the EIS measurement results.Furthermore, the factors affecting the various resistances comprising the equivalent circuit, such as charge transfer, contact, and ionic transport resistances, are discussed, including the dependence of the resistances on the electrode thickness, porosity, and measurement temperature on the resistances.Finally, applications of the EIS of a single electrode obtained using symmetric cells are described, including the prediction of the EIS of LIB and acquisition of the EIS of a single electrode from that of full cells.