Electrochemical impedance spectroscopy: from breakthroughs to functional utility in supercapacitors and batteries – a comprehensive assessment

Electrochemical impedance spectroscopy (EIS) is a powerful technique that can be used to investigate the properties of materials, interfaces, and their redox reactions. It is applied to describe electrochemical systems and support the development of important technologies, offering a much more detailed investigation of properties than other conventional electrochemical techniques. EIS employs a modulated frequency to understand frequency-dependent electrochemical processes, thereby clarifying both fast and slow processes. As a dynamic and robust tool, a thorough understanding of this technique allows the precise use of the information it provides. In this review, we cover the history of the technique's development, its fundamental theory, and necessary conditions for proper use, in addition to providing guidelines on how to use EIS for data collection and the acquisition of relevant information provided by the technique. We also discuss complications related to the necessary conditions, equivalent circuits used for describing systems, commonly used plots, the configuration of electrochemical cells and the possibilities for the use and application of EIS techniques to characterize supercapacitors and batteries. This paper provides meaningful information and discussion related to EIS and ways to better utilize it for investigating the properties of materials.