Electrochemical impedance spectroscopy of battery systems, including sodium materials

An overview is given of the literature on current approaches to the measurement, analysis and interpretation of broadband impedance data and examples of its application to Na materials, cells and batteries. Standard 2-terminal measurements on full cells are often complemented by both 2- and 3-terminal measurements on a range of materials and cell configurations; this should enable identification of the different impedance contributions that control full cell operation. Data analysis usually revolves around equivalent circuit modelling; strategies to identify the most appropriate circuits are reviewed, including the increasing use of the distribution of relaxation times methodology. Interfacial phenomena are fundamental components of solid electrolyte interfaces and composite electrodes in operational batteries; these are reviewed for Na-based materials and systems.