Analytic theory for foil impedance in spiral wound cell geometries

The analytic theory for 1D foil currents and potentials in spiral wound cells with arbitrary tab configurations is derived. The theory is extended to account for state of charge gradients along the length of the foils revealing how tab geometry can affect the slope of constant current voltage curves. Analytic expressions for cell level properties are derived for common tab configurations. The quality of many tab configurations is compared. A straight forward method is described for the common, previously unsolved problem of disentangling the foil and stack contributions of a measured cell impedance. Many other examples of practical problems and solutions are presented. The analytic theory shows how to directly calculate the foil geometry factor introduced in a previous article [1]. Simple methods are presented for adding corrections for foil effects to a stack centric cell model. The analytic results provide a lot of insight and ease of use that numerical solutions cannot easily deliver.