Abstract
Rapid transportation electrification and growing market demand for portable consumer electronics call for revolutionary solid-state Li metal batteries that combine safety and performance to replace commercialised Li-ion batteries that are close to their theoretical limits. Solid-state Li metal batteries still face a challenging scenario to find commercialisation solutions because the Li dendrite growth and the associated short circuit hazards raise public safety concerns. Furthermore, the solid-solid interface is inherently difficult to achieve with comparable performance with their liquid counterparts. This project focuses on developing interface engineering approaches for solid-state Li metal batteries, aiming to realise the technical viability and facilitation of a step change in the energy density of batteries. In this thesis, Chapter 2 systematically reviews previous investigations on interfacial and Li dendrite issues in solid-state Li metal batteries. Recent advances in addressing the interface issues between the Li metal anode and solid-state electrolytes via interface engineering are examined. The characterisation technologies in solid-state electrolytes research, including in-situ implementations, are also summarised. Chapter 3 explores a proof of concept that ion-implantation-induced surface compressive stress can suppress dendrite penetration. The fundamentals of stress in solid-state electrolytes are examined for guiding rational interface stress-strain engineering. The experimental results indicate that sufficient surface compressive stress can prevent the ceramic electrolyte from crack formation and dendrite penetration. In Chapter 4, an electron-rectifying interphase is explored and created to restrain free electrons from infiltrating the solid-state electrolyte. As a result, the Li-ions are not going to be reduced to Li dendrite within the solid-state electrolyte without free electrons, and the cells show a significantly extended lifespan. In Chapter 5, the Li dendrite behaviour and crack formation in the solid-state electrolyte are investigated via 3D reconstructed morphologies obtained using X-ray computed tomography technology. The reconstructed structure indicates crack propagation and porosity increase after the electrochemical process. Time-of-flight secondary ion mass spectrometry attached plasma focused ion beam scanning electron microscopy is applied to characterise the internal chemical information of the electrode materials and the solid-state electrolyte. This technique enables direct observations on the cross-sectional interfaces, featuring high sensitivity on Li-related components.