Successful imaging of electrode cracking relies on sufficient contrast between the mass attenuation coefficients of the active material and the void spaces created by cracks. Xray attenuation is directly related to the thickness and density of the material it penetrates, causing voids within the NMC secondary particles to appear as darker regions in the XCT images (Figure a-d and S11 b-d). The intensity of each voxel is related to materials attenuation within, following a version of the Beer-Lambert law. Greyscale intensity is inversely proportional to X-ray attenuation, so voxels containing voids appear darker than those with NMC material. If a voxel contains both NMC and a crack, the greyscale intensity is reduced, representing a linear combination of the two materials compared to pure NMC (termed 'the partial volume effect'). A voxel fully filled with void/crack shows minimal attenuation, resulting in an extremely low greyscale value. This partial averaging, or partial volume effect, arising from the mixing of NMC and void materials within the same voxel and allows for the detection and quantification of defects that are not visible in the tomogram by eye. Moreover, the greyscale intensity reduction also reflects internal damage, such as cracking, within the particles, and the lower the particle average greyscale the more damaged it may be. Leveraging this phenomenon allows us to obtain information about the extent of defects beyond the spatial resolution of the imaging instrument. This has been observed previously in This demonstrates that high-resolution imaging is not necessary to provide conclusive evidence of cracking occurring within the first cycle. It is also wellestablished that lower-resolution imaging is sufficient for crack detection, as shown by Heenan et al, when artificially reducing the resolution of a cracked particle, the essential information needed for quantifying fracturing is retained. Crack features below the resolution limit of the synchrotron microscope (<325 nm voxel size) are difficult to detect visually, making it challenging to identify significant defects through visual inspection of the tomogram alone. However, greyscale (pixel intensity) analysis is an effective method for crack assessment, where reduced attenuation and lower pixel intensity indicate voids and fracturing, as described above. While the lithium content in the crystal structure varies with lithiation state, its effect on incident energy or impurity presence is negligible. Heenan et al. calculated the changing mass attenuation coefficient of NMC811 at different lithiation states and found that the impact of lithiation is negligible, orders of magnitude less than the background noise, and thus we can confirm that the reduction of grey levels within a particle is uniquely associated with crack or void formation.