Author Archives: joshuagallaway

Let there be more light

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Some new publication news is coming up, because we’ve had two manuscripts accepted this week.

But first, check out this beautiful image from Brookhaven National Lab. Last Wednesday was a terribly rainy day here in New York, but during a break in the rain someone got this great shot of a rainbow, which just happens to begin at the NSLS and end at the NSLS-II.

NSLS Rainbow

“Last light” at the National Synchrotron Light Source (NSLS) was September 30, 2014. “First light” at NSLS-II, its newer, brighter replacement, was October 23, 2014, the morning after the rainbow. NSLS-II, located about halfway out Long Island, will be the world’s brightest light source.

Over the last couple years, this electrochemist has had the good fortune to also become a nascent, sometimes hesitant X-ray spectroscopist. In the messy and interdisciplinary world of battery science there’s a lot of information you need from X-rays, so you can tell what exactly is going on inside batteries while they’re charging and discharging. Batteries contain many secrets, sealed inside their casings. Hopefully we’ll get to learn just as much from NSLS-II as from its storied predecessor. Here’s a photo of me doing research at NSLS just a few days before it shut down:

X-ray Murder

MSU Seminar

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Just got back from giving a seminar at Michigan State University, which has the nicest, greenest campus. I called the talk “Batteries for Massive-Scale Electrical Storage: Using New In Situ Techniques for Electrochemical Systems.”

We had a reunion of some past members of the Scott Calabrese Barton group (pictured below). Leena and Hao both took time out of their busy schedules and drove in. We had a great time. (And the Soup Spoon Cafe was delicious.)

scb reunion

More upcoming work: Probing the materials inside batteries

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This summer we accomplished a lot of further data analysis from a collaboration with researchers at Brookhaven National Lab. We’ve been using cutting edge tools there to identify the materials inside batteries without opening up the battery case, exposing the electrodes to air, or even getting dirty. We published a preliminary paper earlier in 2014, but there is still quite a bit to learn.

BATT FIG

You do this using a technique called EDXRD (or energy dispersive X-ray diffraction). You shine X-ray light with very high energy and very high intensity through the battery. This is called a “white beam” because it has a wide spectrum of wavelengths in it. (That basically means many different “colors” of X-rays. And light with all the colors in it is called “white.”) Some of the light is diffracted by the regularly-occuring patterns of atoms in the battery electrodes, and you set up a detector outside the battery (and several feet away) to measure how much light of each wavelength gets diffracted. Since you’re several feet away and aligned very carefully, you know everything you’re learning pertains to a very small “gauge volume” inside the battery. (In the above cartoon it’s enlarged many times to make it easy to see, but it’s actually cubic microns in size.)

By moving the battery around using a precise x-y-z stage, you can “look around” inside it and see what materials are at every location, provided they’re crystalline enough to diffract X-rays.

AA_capacity1

Take for example a basic rule about batteries: if you discharge them faster you will reduce the capacity you get out of them. The plot above shows discharge curves for two AA alkaline batteries. At a high drain rate of 571 mA you get about 1.7 Ah from the cell, while at 18.1 mA you get double that, about 3.4 Ah. The interesting thing is that these two batteries have entirely different material compositions inside them after discharge. In fact, if you do six different rates, you will get six batteries with six different material profiles in the electrodes. Using a powerful tool like this, you can begin to figure out the extremely complex set of reactions that happen during discharge, which are, believe it or not, largely unknown.

Extracting data from a plot

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All the time I end up trying to extract data from a published plot, for example with the XRD traces above. My brute force method is to load the plot into some image program, then draw straight lines to all the important features. Up above I’ve drawn lines to peaks L, C, G, and F using 30 degrees as the origin. The line lengths tell you exactly where the peak maxima are, after you normalize them to a line drawn along the axis to get the scale.

Hey it’s a decent method and it works, but I was thinking how useful it would be to have a tool that reads an image file and can spit out the original data as a CSV. Turns out there are a few programs that do exactly that. I haven’t tried WebPlotDigitizer yet, but I will soon. If it’s the answer to all my hopes and dreams I’ll let you know.