Hu, Ji; (2025) Advanced characterisation of solid-state electrolytes for Li metal batteries. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Next generation energy storage devices are critical to mitigating climate change and achieving ambitious initiatives such as Net Zero. The use of lithium metal as an electrode material is promising due to its high theoretical capacity but faces challenges due to stability and safety concerns. This thesis examines lithium-ion conducting solid electrolytes due to their important role in these batteries. The work is split into three main topics. First, the investigation of an emerging solid electrolyte material, Li₃AlP₂, is performed. Li₃AlP₂, exhibits variable ionic transport capabilities based on structural defects and disorder. Computational modelling methods, including density functional theory and ab initio molecular dynamics were used to guide material design, while experimental techniques such as electrochemical impedance spectroscopy, nuclear magnetic resonance, and X-ray diffraction validated the simulations. Second, the interfacial properties of Li₃AlP₂ and a state-of-the-art sulfide electrolyte, Li₆PS₅Cl are investigated with the aim of identifying the best candidate for X-ray diffraction computed tomography (XRD-CT) experiments. Li₆PS₅Cl is found to provide a more stable interface against lithium metal and superior ionic conductivity. Finally, XRD-CT, an powerful technique for obtaining 4D information, is employed to study degradation mechanisms in Li₆PS₅Cl in lithium metal symmetric cells. This study identifies and quantifies three distinct degradation mechanisms—mechanical, electrochemical, and chemical—after lithium plating and stripping processes. This thesis provides new insights into materials and device design and the advanced characterization methods described will be applicable to other electrochemical systems.

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