Virginia Tech research study focuses on developing better batteries

Virginia Tech
(© Andriy Blokhin – stock.adobe.com)

It doesn’t come quickly. It can take weeks to notice. You have the newly recharged AA lithium-ion batteries in the cordless cat water fountain, and they last two days. Once they lasted a week or more. Another charge cycle, and they last a day. Soon, nothing.

You would be forgiven if you just stood there and questioned your own actions. “Wait, did I recharge them?” »

Relax, it’s not you. It’s the battery. Nothing lasts forever, not even supposedly long-lasting rechargeable batteries, whether they’re store-bought AA or AAA batteries or the batteries in our cell phones, wireless headphones or cars. Batteries degrade.

Feng Lin, an associate professor in the Department of Chemistry, part of the Virginia Tech College of Science, is part of a new international multi-agency/academic study published today in Science that takes a fresh look at the factors that determine the battery operation. lifespan and how these factors actually change over time under fast charge conditions. At first, the study reveals that battery degradation appears to be driven by the properties of individual electrode particles, but after several dozen charge cycles, it’s how those particles are put together that matters most.

“This study really sheds light on how we can design and manufacture battery electrodes to achieve long battery life,” Lin said. His lab is currently working to redesign battery electrodes with the goal of fabricating electrode architectures that provide fast charging capabilities and longer life at a fraction of the current cost, while being environmentally friendly.

“When the architecture of the electrodes allows each individual particle to respond quickly to electrical signals, we will have a good toolkit for rapidly charging batteries. We are excited to implement the understanding of next-generation batteries, to low cost and fast charging,” Lin said.

The study, of which Lin is a co-lead author, is done in collaboration with the US Department of Energy’s SLAC National Accelerator Laboratory, as well as Purdue University and the European Synchrotron Radiation Facility. Lin lab postdoctoral researchers Zhengrui Xu and Dong Hou, also co-authors of the paper, led electrode manufacturing, battery manufacturing and battery performance measurements, as well as assisting with ray experiments. X and data analysis.

“The fundamental building blocks are these particles that make up the battery electrode, but when you zoom out, these particles interact with each other,” said SLAC scientist Yijin Liu, researcher at the Stanford Synchrotron Radiation Lightsource. (SSRL) and lead author. On paper. Therefore, “if you want to build a better battery, you have to look at how to put the particles together.”

As part of the study, Lin, Liu and other colleagues used computer vision techniques to study how the individual particles that make up a rechargeable battery electrode break down over time. This time, the goal was to study not just individual particles, but also how they work together to extend — or degrade — battery life. The natural end goal: to learn new ways to squeeze a little more life out of battery designs.

As part of their research, the team studied battery cathodes with X-rays. They used X-ray tomography to reconstruct 3D images of battery cathodes after they went through different charge cycles. They then sliced ​​these 3D images into a series of 2D slices and used computer vision methods to identify the particles. In addition to Lin and Liu, the study included Jizhou Li, an SSRL postdoctoral fellow; Keije Zhao, professor of mechanical engineering at Purdue; and Nikhil Sharma, a Purdue graduate student.

The researchers ultimately identified more than 2,000 individual particles, for which they calculated not only individual particle characteristics such as size, shape and surface roughness, but also characteristics such as the frequency at which the particles are coming into direct contact with each other and the variation of the particles. the shapes were.

Then they looked at how each of these properties contributed to particle breakdown, and a striking pattern emerged. After 10 cycles of charging, the most important factors were the properties of the individual particles, including the sphericalness of the particles and the ratio of particle volume to surface area. After 50 cycles, however, pair and group attributes — such as the distance between two particles, the variety of their shapes, and whether more elongated, soccer-ball-shaped particles were oriented the same — resulted in the decay particles.

“It’s not just the particle itself anymore. It’s the particle-particle interactions that matter,” Liu said. “This is important because it means that manufacturers could develop techniques to control these properties. For example, they might be able to use magnetic or electric fields to align elongated particles with each other, which the new findings suggest will result in longer battery life.

Lin added, “We have conducted extensive research on how to operate electric vehicle batteries efficiently under fast-charging and low-temperature conditions.

“Beyond designing new materials that can lower the cost of batteries by using cheaper and more abundant raw materials, our lab has also worked on understanding battery behaviors away from equilibrium,” Lin said. , “We have begun to study battery materials and their response to these harsh conditions.”

Zhao, a Purdue professor and co-lead author, likened the degradation problem to people working in groups. “Battery particles are like people – we all start our own way,” Zhao said. “But eventually we meet other people and we end up as a group, going in the same direction. To understand maximum efficiency, we need to study both individual particle behavior and how those particles behave in groups.

The research was funded by the US Department of Energy, the SLAC National Accelerator Laboratory Research and Development Program, and the National Science Foundation. The SSRL is a user facility of the Department of Energy Office of Science.

Paul N. Strickland