How are they getting color? My impression is CT scan is mostly measuring density and x-ray absorption. Are they doing false color based on some sort of data (vs photoshop?)
The article mentions in passing that "The negative electrode is copper; its yellow color in our visualization means it’s denser than the other materials in the battery." So presumably the blue to yellow scale corresponds to material density.
I think in this case it's just the density (absorption) but on some machines it's possible to use different energy levels of x-rays (so-called dual energy CT) to see variations in materials/chemistry, that works in a similar way to colour in the visual spectrum (different materials absorb different energy levels of light differently).
Looks like a basic CT scan but using the Plasma colormap from matplotlib (or a similar one).