Influence of cell design on impedance characteristics of cylindrical lithium-ion cells: A model-based assessment from electrode to cell level

- Assessment of electrical and electrochemical loss processes in cylindrical lithium-ion cells.
- Spatial and temporal deconvolution of processes by transmission line approach.
- Physically based parametrization by half-cell impedances and geometrical information.
- Detailed analysis of cell design parameters (e.g. collector tab position).

Electrochemical impedance spectroscopy (EIS) is a fast, inexpensive and non-destructive tool for identification of electrical and electrochemical loss processes of battery cells in a wide range of frequencies. Among those, particularly interface processes like the migration of Li species through surface films and the charge transfer reaction are easy accessible by EIS. One of the main drawbacks of its application to commercial cells is the limitation to the full cell spectrum due to the absence of an appropriate reference potential to separate cathodic and anodic contributions. Further, the impedance response of cell geometries such as cylindrical cells is characterized by a complex superposition of contributions arising from electrochemistry and cell design. In this study, we address these issues by a planar transmission line model allowing to reconstruct the impedance response of cylindrical cells by impedance data obtained from three electrode measurements on extracted electrodes and geometrical information obtained from microscopical cross sections. The reconstruction results indicate a substantial contribution from the spiral geometry of the current collectors and the position of the current collector tabs along the jelly roll. Furthermore, the impedance response is significantly determined by the power/energy design of the cell, for instance by the ratio of electrode areas and thicknesses. Overall, the proposed methodology presents a sound modeling basis for a deeper understanding of the impedance response of cylindrical cells and a tool for cell design optimization from electrode to cell level.