Exploring the influence of porosity and thickness on lithium-ion battery electrodes using an image-based model

There is a growing need for lithium-ion batteries that possess increased energy storage capabilities, with a simultaneous requirement for fast charging and improved rate performance. Thick electrodes provide proportionately more active material and thus better storage capabilities, while having the unavoidable characteristic of an increased diffusion length that adversely affects the high rate performance of an electrode. Here, the workflow of advanced X-ray nano-computed tomography (CT) imaging, morphological image processing techniques, and a coupled electrochemical model is established. This tool facilitates the digital alteration of realistic electrode microstructures in a rational manner and permits studies such as the one presented in this work where an extensive parametric study is carried out and assesses the influence of thickness, porosity and discharge rate on electrode performance under the theme of heterogeneity, a key advantage of image-based analysis. In broad terms, the model shows high levels of heterogeneity in lithium, lithium-ion, and current density distributions across the electrode that gives rise to the significant and inextricable link between thickness, porosity and discharge rate. The modelling methodology presented in this work provides a foundation for the design of novel thick battery electrodes, and an example of such a design is presented here. • X-ray image-based model of thick battery electrode microstructures. • Image processing techniques allow analysis and design of realistic microstructures. • Parametric study illustrates limitations arising from porosity and thickness. • Detailed insight of electrode heterogeneities due to sluggish species transport.