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 battery 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) that 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 that performed an internal computerized axial tomography (CAT) scan on lithium batteries in real time so they could see what was going on inside (Figure 1).


Figure 1
Cut-away of battery-containment design attached to the rotation stage for real-time x-ray CAT scan (a); arrangement of apparatus thermal runaway experiments (b); 3D reconstruction with slices in the XY, YZ, and XZ planes of a 2.6 amp-hour battery (Cell 1) with isolated XY slice (c); 3D reconstruction with slices in the XY, YZ, and XZ planes of a 2.2 amp-hour battery (Cell 2) with isolated XY slice (d). Source: Nature and University College London

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
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 (a); 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 (b); grey-scale slice from the XY plane (c). SourceNature and University College London



Figure 3
A 3D image of thermal runaway. Source: University College London

The researchers claim their development of this real-time visibility is a test first; I'll take their word for that, of course. How and what they did, and what they found, makes for a fascinating story, as it wasn't just a simple matter of borrowing an available CAT scanner; there's a synchrotron in the picture and interesting fixturing. You can get details of the story in several ways:

The team at UCL was able to devise, and successfully implement, a technique for watching the internal operation of the electrochemical “black box” we call a battery. Their success made me think: what other electronic-related operations or processes would be nice to observe in real time, and yet not affect the on-going operation itself? What's on your list of things you'd like to see, literally and figuratively?

Bill Schweber is an EE who has written three textbooks, hundreds of technical articles, opinion columns, and product features.


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