Hundreds of batteries sit on massive racks, blinking red and green, and are tested everyday inside Feng Lin's lab at Virginia Tech. The green and red lights mean the testing channels are working. Photo: Feng Lin.
Hundreds of batteries sit on massive racks, blinking red and green, and are tested everyday inside Feng Lin's lab at Virginia Tech. The green and red lights mean the testing channels are working. Photo: Feng Lin.

Nothing lasts forever, not even supposedly long-lasting rechargeable batteries, be they AAs or AAAs bought in store or the batteries inside our cellphones, wireless earbuds or cars. Batteries decay.

Feng Lin, an associate professor in the Department of Chemistry at Virginia Tech, is part of a new international, multi-agency/university research team that has taken a new look behind the factors that drive a battery’s lifespan and how those factors actually change over time in fast-charging conditions. As reported in a paper in Science, the team found that, early on, battery decay seems driven by the properties of individual electrode particles, but after several dozen charging cycles, it’s how those particles are put together that matters more.

“This study really sheds light on how we can design and manufacture battery electrodes to obtain a long cycle-life for batteries,” said Lin, who is a co-senior author of the paper. His lab is now working to redesign battery electrodes with the goal of fabricating electrode architectures that provide fast-charging capabilities and sustain a longer life at a fraction of today’s cost, as well as being environmentally friendly.

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

The study is a collaboration with the US Department of Energy’s SLAC National Accelerator Laboratory, along with Purdue University and the European Synchrotron Radiation Facility in France. The Lin lab’s postdoctoral researchers Zhengrui Xu and Dong Hou, who are co-authors on the paper, led the electrode fabrication, battery manufacturing and battery performance measurements, as well as assisted with X-ray experiments 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, a researcher at the Stanford Synchrotron Radiation Lightsource (SSRL) and a senior author on the paper. Therefore, “if you want to build a better battery, you need 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 apart over time. Their goal was to study not just individual particles, but the ways the particles work together to prolong – or degrade – battery life. The researchers thus hoped to learn new ways to squeeze a little more life out of battery designs.

As part of their research, the researchers studied battery cathodes with X-rays. Using X-ray tomography, they reconstructed 3D pictures of the cathodes of batteries after they had gone through different charging cycles. They then cut up those 3D pictures into a series of 2D slices and used computer vision methods to identify the particles.

The researchers ultimately identified more than 2000 individual particles. They calculated not only individual particle features such as size, shape and surface roughness, but also traits such as how often particles came into direct contact with each other and how varied the particles’ shapes were.

Next, they looked at how each of those properties contributed to the breakdown of the particles, and a striking pattern emerged. After 10 charging cycles, the biggest factors were the properties of individual particles, including how spherical the particles were and the ratio of particle volume to surface area. After 50 cycles, however, pair and group attributes – such as how far apart two particles were, how varied their shapes were, and whether more elongated, football-shaped particles were oriented similarly – drove particle breakdown.

“It’s no longer just the particle itself. It’s particle-particle interactions that matter,” Liu said. “That’s important because it means manufacturers could develop techniques to control such properties. For example, they might be able to use magnetic or electric fields to align elongated particles with each other, which the new results suggest would result in longer battery life.”

“We have been investigating heavily on how to get electric vehicle batteries to work efficiently in fast-charging and low-temperature conditions,” added Lin. “Beyond designing new materials that can lower battery cost by using cheaper, more abundant raw materials, our lab has also been working on understanding battery behaviors far from equilibrium. We have started to study battery materials and their response to these harsh conditions.”

Keije Zhao, a professor of mechanical engineering at Purdue University and a co-senior author, likened the degradation problem to people working in groups. “Battery particles are like people – we all start out going our own way,” Zhao said. “But eventually, we encounter other people and we end up in groups, going in the same direction. To understand peak efficiency, we need to study both the individual behavior of particles and how those particles behave in groups.”

This story is adapted from material from Virginia Tech, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.