I was looking though some research photos and I found this nice example of why post mortem battery analysis is better done by some X-ray technique. Once you start opening things up, you mix the materials around, you oxidize them, etc, unless you have a very good method, which is probably tedious.
Just published a paper called “An in situ synchrotron study of zinc anode planarization by a bismuth additive.” It’s a mechanistic study to explain a result we discovered in the early days of the CUNY Energy Institute. I was looking for an additive to kill dendrite formation in zinc, working with Dan Steingart and Abhinav Gaikwad, who was a graduate student at the time. Turns out a little bit of bismuth can keep zinc layers quite flat when electroplated from a flowing electrolyte. The middle image below shows it clearly:
The percentages are % of the bismuth saturation limit, which is very low. 10% is 3 ppm, an almost undetectable amount, and it has an enormous impact. This result could be used to increase the energy density of zinc batteries, by keeping the zinc layer compact. When naming the paper I called it “planarization” instead of “leveling” because the mechanism is different than that of a leveler in traditional electroplating.
We just had a paper published in The Journal of Materials Chemistry A about some research done at Brookhaven National Lab. It’s cool and new because it uses extremely high-power X-rays that can penetrate thick materials, even metals. The technique was developed to find points of strain inside high-performance materials like turbine blades. We use it to do the same thing, but inside batteries. And not just small batteries, but very thick ones, like D-cell batteries, which are an inch or two across.
Inside the battery, the X-rays bounce off crystal faces of the materials, and because of that you can know things about how far apart the atoms are. A D-cell has zinc at its center (anode) and manganese dioxide around its outside (cathode). The lines in the image above are like fingerprints of these materials. (And the numbers like (002) refer to the crystal faces themselves.)
Another cool thing about this technique is that it is very fast. You can scan the battery in a few minutes. This means that as it’s charging and discharging you can watch the materials changing in real time, inside the sealed battery. Basically this is what we do in the paper, shown below, seeing some things no one has ever been able to see before (except by cracking a battery open after cycling it, which can sometimes be effective, but not always). Brookhaven (on Long Island, in New York) is one of the only places in the world you can do this.
We have a new paper coming out soon. It’s about what happens when zinc and bismuth are electrodeposited together, but the real work was making a very thin flow cell that could fit inside a confined space at a synchrotron beamline. Figure 2 from the paper are pictures from my cell phone I took while setting it all up.
It’s special because the cell had to be thin enough (far less than a millimeter) to let the synchrotron beam through. The section labeled “window” is where that is accomplished. We did this at beamlines X8 and X13 at the National Synchrotron Light Source. More about it later.
Up above there’s a new header image. It’s a zinc dendrite tip imaged using the transmission X-ray microscopy beamline X8C at the National Synchrotron Light Source. Zinc dendrites limit the usefulness of zinc batteries, because they like to grow and puncture battery separators. And if this happens it basically ruins the battery. It’s a cool image because if you look, notice that the dendrite has a more angular appearance to the left, and looks more flowery to the right. That’s because of how I grew it. Why do dendrites grow? That is a complicated question. More on that later.
X-ray microscopy is useful because you can do it without being in a vacuum (which is required when you do electron microscopy). This dendrite was in a flowing water-based electrolyte, just like in a battery. Having that electrolyte present is possible but difficult in a vacuum, but since we’re imaging with X-rays we don’t have to worry about that.