By examining how tiny particles in a lithium ion battery electrode behave, the researchers have shown that rapid-charging the battery and using it to do high-power, rapidly draining work may not be as damaging as had been thought – and that the benefits of slow draining and charging may have been overestimated.
The findings also suggest that scientists may be able to modify electrodes or change the way batteries are charged to promote more uniform charging and discharging and extend battery life.
“The fine detail of what happens in an electrode during charging and discharging is just one of many factors that determine battery life, but it’s one that, until this study, was not adequately understood,” said William Chueh of SIMES, an assistant professor at Stanford’s Department of Materials Science and Engineering and senior author of the study. “We have found a new way to think about battery degradation.”
The results can be directly applied to many oxide and graphite electrodes used in today’s commercial lithium ion batteries and in about half of those under development.
Chueh's team included collaborators from Massachusetts Institute of Technology, Sandia National Laboratories, Samsung Advanced Institute of Technology America and Lawrence Berkeley National Laboratory.
One important source of battery wear and tear is the swelling and shrinking of the negative and positive electrodes as they absorb and release ions from the electrolyte during charging and discharging.
For this study scientists looked at a positive electrode made of billions of nanoparticles of lithium iron phosphate. If most or all of these particles actively participate in charging and discharging, they’ll absorb and release ions more gently and uniformly. But if only a small percentage of particles soak up all of the ions, they’re more likely to crack, degrading the battery’s performance.
Previous studies produced conflicting views of how the nanoparticles behaved. To probe further, researchers made small coin cell batteries, charged them with different levels of current