Capacitive and Diffusive Contributions in Supercapacitors and Batteries: A Critique of b-Value and the ν-ν Model.

Electrochemical energy storage devices run on two fundamentally different processes: charge storage across the double layer and redox reactions. A satisfactory understanding of the underlying mechanism is only possible once the two contributions are deconvoluted. The b-value and the ν -ν model are two familiar steps undertaken to separate these contributions but as it is shown here both metrics are flawed, prone to misinterpretation, frequently invoked without attention to their limitations, and in need of re-examination. After exploring these flaws through the lens of a diverse set of cyclic voltammetry data we opine that use of the b-value be discouraged on account of subjectivity inherent to the metric, and the ν -ν model be replaced by the one proposed here. This new model ultimately reduces the root mean square error significantly and provides a robust tool for the evaluation of energy storage devices.