Contrast variation is visible inside the single crystal particles (Fig. ). Two types of internal contrast variation could be observed, one with large amplitude and one with a much weaker shift in greyscale value. The smaller variations in greyscale value may be associated with local compositional heterogeneity of the Ni:Mn:Co ratio. Unfortunately, those variations are very close to the image background noise, and cannot be confidently assigned without higher resolution spectroscopic imaging. The larger contrast variation is apparent as dark spots inside the particle, and are attributed to internal porosity/voids, and/or microcracks inside the particles. Details concerning both sets of contrast variation are provided in the Supplementary Information. Some voids are clearly visible, and have well defined shapes (Fig. red arrows). However, smaller voids, including microcracks ≤ 50 nm are incompletely resolved and present as heightened image noise. While previous investigations have shown that single crystals may contain a few microcracks or voids, from these images it is clear that these voids can represent a significant volumetric fraction of the crystals.Depending on the particle selected and due to resolution limits , only 65-90% of the voids can be resolved (i.e. ≥ 50 nm). It is not possible to fully quantify this void volume fraction with certainty, but rather approximate its minimum value around 10% (Fig. ).