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.