A puzzle has baffled the battery industry for decades: certain materials used in the lithium-ion batteries that power our laptops, phones and cars store much more energy than theoretically expected.
Thanks to a research collaboration spanning three countries, this puzzle has been solved and researchers see opportunities to develop new technologies from batteries to quantum devices.
Researchers at the Institute for Quantum Computing (IQC), the Massachusetts Institute of Technology and the University of Texas at Austin, as well as Qingdao University and Shandong University in China, harnessed a technique normally used in physics to investigate batteries and discover their inner workings.
“The challenge is probing what’s going on inside of a battery non-destructively while it is operating,” said Guo-Xing Miao, associate professor at IQC and in the University of Waterloo Department of Electrical and Computer Engineering.
When you charge a battery by plugging it in or discharge a battery by using it, you may also change the magnetism within the battery. The researchers took advantage of this fact and used an in situ magnetometry technique to probe the internal magnetism of a battery in real time.
In a work published in Nature Materials in August 2020, they found that the extra capacity of transition-metal oxides often used as electrodes in lithium-ion batteries mostly resides in nanoparticles that physically collect around the surface of these materials after regular use of the battery. These clouds of nanoparticles hold the extra charge that has puzzled researchers for decades when only chemical reactions had been taken into consideration.
The researchers followed up this work by extending their results from iron oxide to cobalt oxide, another material with an unexpectedly high electrical storage capacity.
Published in Advanced Materials February 2021, the new work demonstrated that a polymer forms on the surface of cobalt oxide during normal use of the battery. The researchers used the magnetometry technique to show that this polymer, with the assistance of cobalt’s catalytic properties, contributes to the extra storage capacity of cobalt oxide electrodes, in addition to the same nanoparticles that benefit iron oxide.
“Most commercial batteries will have a mixture at different transition-metal elements to balance their capacity, stability and cost,” said Miao. “With applied magnetic fields, batteries using these different elements can show magnetic signatures during the reactions as a non-destructive probing method.”
Now that researchers can probe the magnetic changes taking place in many different electrode materials, new avenues of understanding and developing battery technology can be explored.
Miao is also interested to see how this magnetometry technique can impact the next generation of quantum devices. “We borrowed this technique from spintronics where it functions the same, but with different applications,” said Miao.
Qiang Li, the lead author of the paper and an alumnus of Miao’s group, now pursues his own research into spintronics as a professor at Qingdao University and an IQC Affiliate. “I became very interested in magnetism during my time at IQC,” said Li. “The magnetic manipulation with lithium ions is so powerful that it also opens a new route for controlling spintronic devices.”
Spintronics is the study of electron spin in solid state devices. By using the same magnetometry technique that allows them to probe batteries, researchers can read and write magnetic information at the level of the electron in spintronic devices, with ions as the new control knobs.
“In the same way that we can use an electric field to drive ion motion to change the magnetism in a battery, we can change the magnetism in a spintronic device to read or write information, or even to process information using logic gates,” said Miao.
Whether it is probing materials to find an advantage in the batteries that surround us or building the powerful quantum devices of the future, these new developments prove that sometimes the right piece to solve a puzzle is already out there. It just needs to be placed in the right spot.
Extra storage capacity in transition metal oxide lithium-ion batteries revealed by in situ magnetometry was published in Nature Materials August 17, 2020. Operando Magnetometry Probing the Charge Storage Mechanism of CoO Lithium Ion Batteries was published in Advanced Materials February 12, 2021.