It is reported that after a certain number of charge and discharge cycles, lithium-ion batteries will inevitably be scrapped. In order to prolong their life as much as possible, researchers all over the world are also making unremitting efforts The latest news is that in an article published in science on April 29, 2022, SLAC National Accelerator Laboratory of the U.S. Department of energy, together with researchers from Purdue University, Virginia Tech and European Synchrotron Radiation Facility, jointly explored the deep reasons behind battery attenuation.
A positive electrode of a battery that has undergone 10 charge and discharge cycles
At first, the attenuation seems to be driven by the characteristics of individual electrode particles. However, after dozens of charge discharge cycles, how these particles are organized together becomes more important.
Yijin Liu, SLAC scientist, Stanford synchrotron radiation source researcher and senior author of the study, said:
These particles that make up the battery electrode belong to the most basic building blocks. But when you zoom in, you notice the interaction of these particles.
Because of this, if you want to build a better battery, you must deeply understand how these particles are combined.
The focus of this research is not only on individual particles, but also on their cooperative work to find patterns that affect their lifetime.
Therefore, based on previous research, Liu and his colleagues used computer vision technology to study how the single particle constituting the electrode of rechargeable battery decomposes over time.
Keije Zhao, senior author of the study and professor of mechanical engineering at Purdue University, and Feng Lin, Professor of chemistry at Virginia Tech University, take people as examples:
At first, the battery particles went their own way. But in the end, they will bump into each other and work hard together in a certain direction.
To understand peak efficiency, we must deeply study the individuals of particles and their behavior in groups.
(portal: Science)
In order to explore this idea, Jizhou Li, a postdoctoral researcher of SSRL and Nikhil Sharma, a graduate student of Purdue University, cooperated with other colleagues to study the cathode of the battery with X-rays.
After 10 or 50 charge and discharge cycles, they reconstructed 3D images with X-ray tomography, then divided these 3D images into a series of 2D slices, and used computer vision to identify particles.
Finally, they determined 2000 + single particles, calculated not only the size, shape, surface roughness and other characteristics of each particle, but also more global characteristics, such as the frequency of particles contacting each other and the degree of shape change.
Next, they studied how these subdivision characteristics lead to particle decomposition, and found a pattern that can not be ignored - that is, after 10 charge and discharge cycles, the characteristics of a single particle have the greatest impact, including the sphericity of the particle and the volume / surface area ratio.
However, after 50 cycles, how far apart the two particles are, how much their shape has changed, and whether the more slender football shaped particles have similar orientations have played a greater role in promoting particle decomposition.
Yijin Liu added: in other words, the interaction between particles becomes more important than a single particle. Based on this, lithium battery manufacturers can try to develop relevant technologies to control this characteristic.
For example, they can use magnetic or electric fields to align slender particles with each other. New research has shown that doing so can help prolong the service life of batteries.