Predicting the formation of mud cracks in Li-ion battery electrodes during the drying process with in situ X-ray computed tomography

Drying of slurry cast electrodes is amongst the most energy intensive unit operations in battery manufacture. In spite of this, the optimisation of drying processes has been highly empirical, and there remains limited understanding of the interplay between drying dynamics and resulting microstructure. In this work, we used synchrotron X-ray computed microtomography in order to study the formation of mud cracks during the drying process, and evaluate their impact on the electrode microstructure. This was achieved by applying a reduced drying rate, which proved to be an effective means of studying the drying mechanism with a greater resolution and image contrast than otherwise possible. The rate of crack growth is measured, and the differing crack morphology resultant from changes in thickness (between 300 and 800 µm doctor blade gaps) and the presence of air bubbles in the slurry is demonstrated. Digital volume correlation is utilised to identify the specific location of crack formation before these cracks were visible, suggesting image correlation methods as an appropriate tool for process feedback in order to control or eliminate mud cracking. This new approach which enables direct quantification of the evolving microstructure during dynamic drying, in 3D, is therefore transformative in our understanding of the underlying physical processes and will guide rational optimisation of this industrially significant process.