Dawson, Will J; (2025) Analysis of the Formation and Impacts of Mud Cracking in Li-ion Battery Electrodes. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The drying process of Li-ion batteries contributes significantly to both their manufacturing cost and electrochemical and mechanical performance. Mud cracking is a mechanical defect which occurs spontaneously as a result of capillary pressure during the final stages of the drying process. This thesis investigates the causes of mud cracking, the mechanism of their formation and their impact on ion transport and electrochemical performance. At the core of the work is the observation that mud cracks are qualitatively similar to engineered vertical channels, which have been introduced into Li-ion battery electrodes by a variety of manufacturing methods in order to enhance ion transport and improve capacity at high charge rates or in thick electrodes. It was shown that cracks enhance potential ion flux through the electrode thickness to a greater degree than by increasing porosity by the same volume. Cracked electrodes of 70 – 130 µm dry thickness were shown to have improved discharge capacities at rates of 1 – 4 C, compared with uncracked electrodes of equivalent thickness - as much as 68 % higher capacity retention at 4C. These performance enhancements were related to 3D crack network structures determined by X-ray computed tomography imaging, which analysis showed that the arrangement of pore channels is of importance in determining the efficacy of vertical porosity in improving electrode performance. Image-based electrochemical modelling was investigated as a tool for better understanding experimental electrochemical data, and this work highlighted the value of multi-modal model validation, including literature synchrotron studies. The formation of mud cracks during the electrode drying process was studied using in situ X-ray computed tomography. This imaging showed the microstructural evolution of battery electrodes during the drying process with unprecedented clarity and resolution, as well as the relationship between crack growth and local microstructural features. Cracking intensity and morphology were shown to be strongly influenced by coating thickness, in agreement with prior literature, as was the delamination which occurs with severe cracking. Cracks were also shown to nucleate where air bubbles are present in the slurry, and this mode of crack growth was shown to differ markedly from cracks in bubble-free coatings.

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