We talked about how light reflects off things, and how if you looked at a mirror at different angles you might get a blast of reflected light in your eyes. We also talked about how we were using light reflections to study batteries. How do they tie together?
Instead of your eyes use a detector, which is just something that senses light (like your eyes do). A beam of light (X-rays) goes through a battery with a hole in it. Most of the X-ray light goes straight through, but some of it hits the atoms in the battery material and bounces off. So the atoms are like little mirrors. And the detector finds out what angles the light gets bounced off at.
This is an “in situ” experiment because you can discharge and charge the battery while the experiment is happening. In situ is a fancy word scientists like to say that is Latin for “in position.” What it really means is that you don’t have to discharge the battery then take it somewhere else to shine light through it. It all happens in one place. (The opposite of in situ is “ex situ.”)