Young, Robert Scott; (2025) Correlated Characterization and Advanced Microscopy of Sulfidic Solid-State Li Batteries. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The development of safe, high-energy-density storage devices has driven significant advancements in the field of lithium-ion batteries (LIBs), with solid-state batteries (SSBs) emerging as a promising next-generation energy storage solution. However, the transition to solid-state electrolytes (SEs) introduces novel degradation mechanisms, both mechanical and electro/chemical modalities that need to be better understood before widespread adoption. Here, advanced characterization methods are explored that aim to help further the understanding of the complexity of SSB degradation. The X-ray computed tomography (XCT) based degradation studies here focus on Li | Li6PS5Cl | Li symmetric cells cycled under constant current conditions and track the propagation of cracks/voids. Early results highlighted that degradation has a strong dependence on cell design and manufacturing, demonstrating the necessity of informed structural considerations in producing representative electrochemical cells.  To further investigate the impact of mechanical and chemical degradation, a correlated characterization approach is utilized where XCT is combined with X-ray diffraction computed tomography (XRD-CT). Correlated XCT and XRD-CT datasets shed more light on the novel degradation mechanisms, showcasing the impact of pre-cycling defects on the SE, and exemplify how strain leads to cracks that allow Li to penetrate the SE.  Further advancements in degradation characterization are achieved through the integration of neutron computed tomography (NCT), another technique that is complementary to XCT. Because NCT is sensitive to Li, unlike XCT, a vital question can be answered: where is the Li metal plating during cycling and how does that contribute to degradation? The correlated imaging approach of studying SE degradation provides tremendous information about the early stages of defect nucleation, informing the design of future SSBs. This work serves as a foundation for further development in high spatiotemporal resolution studies of SEs, addressing key challenges in understanding degradation pathways and guiding advancements in SSB design and optimization.

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