A recent study at Stanford University on the behavior of tiny particles in lithium-ion battery electrodes suggests that rapid charging followed by high-power, rapid-discharge operation may not damage batteries as badly as researchers initially thought, and the benefits of slow charging and discharging may have been exaggerated. This finding challenges the prevailing view that "supercharged" batteries place higher demands on electrodes than slow-charging batteries, according to researchers from Stanford University and the Stanford Materials and Energy Sciences (SIMES) department at the U.S. Department of Energy's SLAC National Accelerator Laboratory. They also suggest that scientists may be able to extend battery life by modifying battery electrodes or changing charging methods to improve the uniformity of the charging and discharging process.
“The details of the chemical processes that occur within the electrodes during charging and discharging are just one of many factors that determine battery life, but one that was not fully understood before this study,” said William Chueh, senior author of the study, assistant professor of materials science and engineering at Stanford University and a member of SIMES. “We have discovered a new perspective on studying battery aging.” These findings can be directly applied to oxide and graphite electrodes used in many modern commercial lithium-ion batteries.
This research was published in the September 14th issue of the journal *Nature Materials*. The research team also included collaborators from MIT, Sandia National Laboratories, Samsung Advanced Institute of Technology, and Lawrence Berkeley National Laboratory.
Observe the ions in the battery cell
A major cause of battery degradation is the expansion and contraction of the positive and negative electrodes during charging and discharging, as they absorb and release ions from the electrolyte. In this study, scientists investigated a positive electrode composed of billions of lithium iron phosphate nanoparticles. If most or all ions actively participate in the charging and discharging process, they will absorb and release ions relatively uniformly. However, if only a small number of particles absorb all the ions, they are more likely to break down and become damaged, reducing battery life.
Conflicting views have emerged regarding the properties and behavior of nanoparticles compared to previous research. To further investigate the truth, researchers fabricated miniature coin batteries, charging them with different currents for varying durations, then rapidly separating them and flushing the components to halt the charging/discharging process. The scientists then sliced the electrodes into extremely thin sheets and sent them to Berkeley National Laboratory for analysis using the dense X-ray beams of the Advanced Light Source synchrotron.
New insights into rapid discharge
“We can study thousands of electrode nanoparticles at once and take snapshots of different stages of the charging and discharging process,” said Yiyang Li, the study’s lead author and a graduate student at Stanford University. “This study is the first detailed and comprehensive investigation of the charging and discharging process under different charging and discharging conditions.”
By analyzing data using a well-established model developed by MIT, researchers discovered that only a small fraction of nanoparticles absorb and release ions during charging, even though this process occurs very rapidly. However, something interesting happens when the battery discharges: as the discharge rate exceeds a certain limit, more and more particles begin to absorb ions synchronously, transitioning to a more uniform and less damaging pattern. This suggests that scientists may be able to manipulate electrode materials or this process to achieve either longer battery life or faster charging and discharging rates.
According to Li, the next step is to run the battery electrodes through hundreds or even thousands of cycles to simulate real-world conditions. Scientists hope to capture snapshots of the battery during charging and discharging, rather than interrupting the process and separating the battery components. This should provide more realistic insights, and the process can be conducted in synchrotrons, such as ALS or SLAC at the Stanford Synchrotron Radiation Facility. Li also stated that the research team is currently working closely with industry to investigate how these findings will be applied to the transportation and consumer electronics sectors.
This research was supported by funding from the Samsung Advanced Institute of Technology's Global Innovation Expansion Program, Stanford University's School of Engineering and Precord School of Energy, the Samsung-MIT Energy Applications Materials Design Program, and the U.S. Department of Energy.
