Randjbar Daemi, Sohrab; (2019) Development of Advanced X-ray Tomography Techniques for Li-ion Electrode Characterisation. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Lithium ion batteries are becoming the preferred energy storage devices for portable and stationary applications as their specific power and energy densities can be adapted to fit specific requirements. The electrochemical reactions occurring during charge and discharge operations generally take place on complex porous electrodes. While electrode microstructure has a determining effect on battery performance, their manufacturing parameters are often determined empirically. Furthermore, the reciprocal link between electrode microstructure and resulting performance is poorly understood. X-ray tomography techniques allow for the non-destructive characterisation of battery materials across different length-scales and have emerged, over the last decade, as a powerful tool for battery electrode characterisation. The studies presented in this work present several approaches to apply ex and in situ X-ray tomography techniques to investigate the structure-property relationship of battery materials. In the first instance, a suite of advanced computational and experimental techniques are developed and applied to analyse the active and inactive phases of a transition metal oxide cathode in the micro- and nano-domains. Furthermore a correlative approach to understand the contribution of the carbon binder domain to the overall transport properties of the electrode is presented. While ex situ approaches can be applied with greater ease due to a relatively more trivial sample preparation, the spatial localisation of observed phenomena is not possible due to the fact that different samples are analysed each time. Two avenues for in situ characterisation using X-ray computed tomography are presented. Specifically, the development of optimised in situ cells for lab-based tomography and a technique to image battery electrodes on the nano-scale whilst they are being compressed are presented. Finally, X-ray diffraction computed tomography is used to gain information on the crystallographic change battery electrodes undergo as a result of cycling to different upper cut-off voltages. This technique complements the previous microstructural studies by adding a diffraction analysis. Overall, these techniques open the scope of applying X-ray tomography based techniques to further the understanding of the structure-property relationship of electrode materials and optimise their design for high-performance applications.

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