Batteries are tough to test in both the R&D phases. Sure, you can measure the voltage, charge flow, and temperature, and even physical dimension changes, but after that, it’s a struggle to see what’s going on internally. However, since batteries improvements are of such high interest, there are few limits that researchers won’t investigate to gain real insight.
For example, I just came across a set of articles and an academic paper by a team at University College London (UCL) which clearly illustrates the extremes to which the battery-test community will go to see what is otherwise not seeable. The team developed a complex set-up which performed an internal computerized axial tomography (CAT) scan on lithium batteries in real time so they could see what going on inside, Figure 1 .
Figure 1 (a) Cut-away of battery-containment design attached to the rotation stage for real-time x-ray CAT scan; (b) arrangement of apparatus thermal runaway experiments; (c) 3D reconstruction with slices in the XY, YZ, and XZ planes of a 2.6 amp-hour battery (Cell 1) with isolated XY slice; (d) 3D reconstruction with slices in the XY, YZ, and XZ planes of a 2.2 amp-hour battery (Cell 2) with isolated XY slice. (Image source: University College London and Nature )
The objective was to get detailed insight into the unfortunate and well-known, but hard-to-decode, aspect of these batteries: their tendency to overheat and explode/catch fire under some circumstances, which is dramatically and quite correctly called thermal runaway, Figure 2 . This has happened in large and small battery packs, such as the Boeing Dreamliner 787 aircraft, hoverboards, and even unplugged laptops.
Figure 2 (a) External view of Cell 2 after thermal runaway showing the burst cap and protruding internal contents. The black marks indicate the points at which the bottom slice of the corresponding tomogram begins; (b) 3D reconstruction showing isolated copper phase (yellow), other broken-down material (semi-transparent dark grey) and battery casing (blue) where the copper phase is mostly still intact. (Image source: University College London and Nature )