Development of X-ray Tomography Tools for Characterisation of Lithium-Sulfur Batteries

Electrochemical energy storage devices are becoming increasingly ubiquitous in both consumer and industrial applications, driven by a pressing need to reduce carbon emissions for the mitigation of global warming. The electrification of the transport and mobility sector and growth in portable electronic devices demand portable power sources with high energy densities, and lithium-ion (Li-ion) batteries have been adopted extensively in these applications. However, conventional transition metal oxide-based intercalation materials used at the positive electrode are reaching their theoretical limitations, and only relatively minor improvements in theoretical specific capacity can be achieved. // Lithium-sulfur (Li-S) batteries offer higher gravimetric theoretical specific capacity and energy density and are billed as a potential successor to Li-ion technology but suffer from limited cycle life and self-discharge due to complex multi-phase chemistry and parasitic side reactions. // To better understand the fundamental mechanisms behind these processes, advanced characterisation methods involving the use of penetrating radiation (such as X-rays and neutrons) have become invaluable tools to capture the operation and degradation of the Li-S battery. Three-dimensional techniques such as X-ray micro-tomography (micro-CT) are particularly suited to probe the heterogeneous nature of battery electrode microstructures. // In this thesis, main areas of focus will include the application of ex situ and in situ X-ray micro-CT on Li-S batteries and the broader development of in situ tomography cells. The overall scientific aims of this thesis include: measuring the three-dimensional microstructural characteristics of sulfur electrodes; elucidating the three-dimensional nature of both sulfur dissolution and redeposition as a function of state of charge; and developing a better understanding of the transport processes occurring within the Li-S battery and the influence of porosity and tortuosity on electrochemical performance. In parallel, the development of in situ tomography cells capable of electrochemical cycling is an extensive component of this thesis, with applications not solely limited to Li-S batteries or X-ray micro-CT