Researchers use MRI to peer into batteries

Exploding batteries are not what you want to hear about when there is a cellphone in every pocket and bag. So a team of researchers has developed a diagnostic method for figuring out why batteries fail. Instead of cutting into the batteries and potentially destroying evidence in the process, the new technique uses an MRI to give a noninvasive picture of what's going on.
If medical dramas have taught us anything, though, it's that patients with metal rods in their legs can't get MRIs. So it may seem odd to put a battery in the giant magnet machine. The researchers, who published their findings in Nature Materials this week, had some properties of matter on their side, though.
For one thing, many metals are not magnetic and can actually cause more problems by warping images than by flying across the room. "Most metals are actually nonmagnetic," Alexej Jerschow, a contributor to the research from NYU, said. "But metal does distort images in MRI so that is something we have to pay attention to. We had to be very careful with how the battery is oriented with respect to the apparatus."
The group, comprised of researchers from Cambridge, Stony Brook and New York University, used their technique to look at the electrodes of lithium ion batteries. MRI radio waves cannot penetrate very far into metal, but the researchers actually took advantage of this to focus on identifying subtle surface changes in the batteries that might cause problems.
The researchers thought to use MRIs because other noninvasive techniques, such as neutron imaging, that shoot subatomic particles through running batteries to gather data are complicated and have drawbacks.
In testing their method, the researchers found that microstructure build-up, or gunk, was accumulating on the electrodes after repeated charging. They looked at how this might be affecting the performance of the batteries by using the MRI data to produce three-dimensional figures for analysis. Some represented the "pristine state" of the lithium before charging and others showed its disturbed state after charging.
"It is a very good example of a technique that I suspect will be used quite a bit in trying to improve current technologies," Tyrel McQueen, a solid state and inorganic chemistry researcher at Hopkins said.
He pointed out, though, that the method may unearth limitations in addition to facilitating advances. "Batteries on the one hand are amazing technology, because I look at what the lithium ion battery is capable of today and a decade ago that would have been unheard of. But on the other hand I think one has to be careful in not putting batteries where they don't have strength."
With batteries being called on to power increasingly demanding devices, their shortcomings are become more apparent. Their longevity, capacity and ability to recharge quickly are all limited. And for large instruments like cars an additional problem is the rate at which energy can exit the battery for acceleration.
"I definitely think this is a big step forward," Jerschow said. "It's opening a new field where you have new abilities to assess batteries and look inside them. There are limitations of sensitivity, but its biggest strength is that you can make nondestructive measurements and we will go as far as we can with that."