Standardization and normalization of capacity vs. current rate behavior of intercalation electrodes for Li-ion and Na-ion batteries

The improvement of intercalation electrodes, especially the cathodes, for Li-ion and Na-ion batteries requires a deep understanding of the relationships between the properties of the active materials and the variables introduced by the electrode/cell manufacturing strategies (e.g. carbon-based additives, binders, etc.). Starting from the specific experimental capacity (C) and its relationships with the cell charge-discharge rate (R), we propose standardization and normalization parameters and procedures for a vast category of intercalation cathode materials, whose results are given from the literature. The approach is successfully demonstrated for different electrode materials. Despite of the complex chemistry on which Li/Na-ion cells operation is based, the applicability and comprehensiveness of our simple relationship is supported by the general underlying diffusion theory, governing nearly all the cases, and by simple assumptions established by experiments. Our approach offers a clear numerical basis for evaluating the goodness of R-C characteristics, as well as simple criteria for evaluating the cell performance. In the case of poor performance, we show how to separate the contribution of the material from the strategies of the electrode/cell assembly. In the future, this standardization/normalization strategy can also be useful to tackle the issues of battery state-of-health, favoring the correct choices of recycling/reuse in a circular economy perspective.