Lithium-ion battery (LIB) safety is a multi-scale problem: from the whole-cell architecture to its composite internal 3D microstructures. Substantial research is required to standardise failure assessments and optimise cell designs to reduce the risks of LIB failure. In this work, the failure response of a 1 Ah layered pouch cell with a commercially available NMC cathode and graphite anode at 100 % SOC (4.2 V) is investigated. The mechanisms of two abuse methods; mechanical (by nail penetration) and thermal (by accelerating rate calorimetry) are compared by using a suite of post-mortem analysis methods. Post-mortem whole-cell architectural changes and electrode layer deformations were analysed for both mechanisms using non-invasive X-ray computed tomography. Furthermore, changes to electrode surfaces, bulk microstructures and particle morphologies are compared by following a proposed cell disassembly and post-mortem sample preparation methodology. Building on the insights into critical architectural weak points, electrode behaviours and particle cracks, the reliability of X-ray computed tomography as a guide for LIB failure assessment is demonstrated.