Operando tomographic characterisations of solid-state lithium metal batteries

Abstract

This thesis studies the mechanical degradation and ionic diffusion within solid-state lithium metal batteries using multi-scale operando tomographic characterisations, aiming to address key challenges in lithium metal anode and composite cathodes, and realise high-performance solid-state batteries with fast charging capability and cycling stability. Chapter 3 investigates the effectiveness of multi-layered solid electrolytes in inhibiting lithium dendritic propagation. Adding an inner layer solid electrolyte, Li3ScCl6 or Li10GeP2S12, within the primary solid electrolyte is observed to prevent short circuit by deflecting dendritic cracks along the interface between different layers and within the inner layer. The crack deflection is proved to have a mechanical origin. Dendritic cracks are prone to be deflected by weak interfaces resulting from the dissimilar elastic modulus between layers and inhomogeneous microstructure within one layer. Chapter 4 comprehensively investigates the electro-chemo-mechanical interactions within solid-state lithium metal batteries across different length scales, with emphasis on the mechanical dynamics of cathode active materials and solid electrolytes within composite cathodes, primarily arising from electrode volume change. Utilising synchrotron imaging techniques including operando X-ray ptychographic laminography and operando X-ray computed tomography, the study captures and analyses microstructural alterations and strain evolution at particle, electrode, and battery levels. Insights obtained inform strategies aimed at enhancing the mechanical stability of composite cathodes. Chapter 5 delves into the ionic diffusion behaviour within high-loading composite cathodes. Operando neutron radiography and operando spatially resolved X-ray diffraction reveal phenomena of non-uniform lithiation and delithiation along the depth of composite cathodes, resulting from limited ionic conductivity. Key findings include asymmetry in lithium diffusion during lithiation/delithiation, inter-particle ion diffusion during rest, and establishment of a relationship between local state of charge and cell voltage. The asymmetric and spatially inhomogeneous ionic diffusion leads to significantly faster charge/discharge rates for local cathode particles.