Researchers have identified a key reason why the batteries used to power everything from smartphones to electric vehicles deteriorate over time, a critical step toward building faster, more reliable and longer-lasting batteries.
The research team from The University of Texas at Austin, Northeastern University, Stanford University and Argonne National Laboratory found that every cycle of charge and discharge causes batteries to expand and contract, similar to human breathing. This action causes battery components to warp just a tiny amount, putting strain on the battery and weakening it over time. This phenomenon, known as "chemomechanical degradation," leads to reduced performance and lifespan.
The findings shed new light on an issue that has puzzled scientists and engineers worldwide.
"With every 'breath' of the battery, there's some degree of irreversibility," said Yijin Liu, an associate professor in the Cockrell School of Engineering's Walker Department of Mechanical Engineering and Texas Materials Institute and leader of the study published in Science. "This effect accumulates over time, eventually causing failure of the cell."
One of the key discoveries was the identification of "strain cascades" - a chain reaction in which stress builds up in one part of the electrode and spreads to neighboring regions. The unique nature and unpredictable movements of the hundreds of thousands of particles in batteries contribute to this strain.
"We were able to see that every particle behaves differently under electrochemical stress," said Juner Zhu, assistant professor of mechanical and industrial engineering at Northeastern and one of the co-authors. "Some particles move rapidly, like shooting stars in the sky, while others remain relatively stable. This uneven behavior creates localized stress that can lead to cracks and other damage."
By understanding how strain develops and spreads, engineers can create electrodes that are more resistant to stress and degradation. For example, the study suggests that applying controlled pressure to battery cells could help mitigate strain and enhance performance.
"Our ultimate goal is the creation of advanced technologies that can substantially increase the utility and durability of batteries," said Jason Croy, co-author and group leader for the Materials Research Group at Argonne National Laboratory. "Understanding how the design of electrodes influences their response to stress is a critical step in pushing the boundaries of what batteries can do."
To discover this new information, the research team employed advanced imaging techniques to observe battery electrodes in real time during charging and discharging. Using state-of-the-art tools like operando transmission X-ray microscopy (TXM) and 3D X-ray laminography, they captured detailed images of how particles within the electrodes move and interact.
The researchers first observed this dynamic in a device used for another research project, commercial earbuds. The researchers plan to continue on this path, with the next step focusing on developing theoretical models to further understand the complex interactions between chemical and mechanical processes in battery electrodes.
The research was funded through the U.S. Department of Energy's Vehicle Technologies Office. The other members of the team are Tianxiao Sun, Guannan Qian, Wenlong Li, Shimao Deng and professor Guihua Yu of UT's Materials Science and Engineering Program and mechanical engineering department; Ruqing Fang of Northeastern University; Guibin Zan and Wenbing Yun of Sigray Inc.; Zhichen Xue, professors Will Chueh and Piero Pianetta of Stanford and SLAC National Accelerator Laboratory; and Stephen E. Trask, Arturo Gutierrez and Luxi Li of Argonne National Laboratory.
