One of the critical needs for the next generation of energy storage devices is to make more energy dense batteries, that are safe and stable over long-term cycling. Solid-state batteries (SSBs): with a combination of a Li metal anode and solid-state electrolyte (SSE) could be a potential solution to address these needs. However, they are currently limited in commercial applicability, as their cyclic stability and safety, especially at higher current densities needs addressing. This is primarily due to ‘electro-chemo-mechanical’ degradation at the interface of the SSE with Li metal, which causes cell shorting. In this work, we characterize sulphide-based SSEs against a Li metal anode, using a combination of synchrotron-based X-ray microcomputed tomography (µ-CT), X-ray diffraction computed tomography (XRD-CT), and electrochemical impedance spectroscopy (EIS). µ-CT provides the evolution of morphological degradation (voids/cracks) through the SSB, while XRD-CT provides maps of the secondary chemical and electrochemical reaction products produced over cycling. EIS helps to link these local (microscale) deformation fields to the global (device scale) performance of the cell, measured in terms of the capacity/impedance of the cell. In addition, XRD-CT allows for tying these degradation methods to the associated strain-fields, and study their evolution from beginning to end-of-life condition of the cell. By using this combination of local and global methods, we first separate the effect of SSE processing, cell assembly, and electrochemical cycling on cell degradation. We find the mechanical stress around deformation hotspots to far exceed the elastic limit of Li, thus showing the mechanical underpinnings of Li metal filling cracks in the SSE, leading to shorting of the cell. We show how the rate of nucleation/growth of these degradation pathways, and their heterogeneity vary with materials processing (sintering/pressing), and with the current density during electrochemical cycling. Finally, the interaction of local mechanical degradation of the SSE with the global stress state of the cell is discussed, in terms of crack mitigation strategies. We envisage that this approach with the objective of isolating degradation mechanisms, and directly tying them to their associated deformation fields effectively reduces a complex electro-chemo-mechanical problem into a stress minimization problem. This will in turn lead to the rational design of improved devices.