Jianming Bai, Feng Wang, Wei Zhang, Yimei Zhu, and Lijun Wu are scientists at Brookhaven’s TEM facility. Together they observed lithium depleting inside nanoparticles, using electron microscopy and x-ray imaging, while a battery was generating current, concentrations were previously thought to constantly increase.
Stony Brook University’s Esther Takeuchi commented: “If you have a cell phone, you likely need to charge its battery every day, due to the limited capacity of the battery’s electrodes. The findings in this study could help develop batteries that charge faster and last longer.”
A regular lattice structure defines the arrangement of atoms in the battery, and includes space between each one. When it is in operation, ions flow into and through the spaces.
Wei Zhang explained: “Previously, scientists assumed that the concentration of lithium would continuously increase in the lattice. But now, we have seen that this may not be true when the battery’s electrodes are made from nano-sized particles. We observed the lithium concentration within local regions of nanoparticles go up, and then down—it reversed.”
Feng Wang added: “Similar to how a sponge soaks up water, we can see the overall level of lithium continuously increase inside the nano-sized particles, but unlike water, lithium may preferentially move out of some areas, creating inconsistent levels of lithium across the lattice.”
“Before lithium enters the lattice, its structure is very uniform, but once lithium goes in, it stretches the lattice, and when lithium goes out, the lattice shrinks. So each time you charge and drain a battery, its active component will be stressed, and its quality will degrade over time. Therefore, it is important to characterise and understand how lithium concentration changes both in space and time.”
The University of Michigan’s Katsuyo Thornton also commented on the study: “We initially thought that the reversal mechanism was similar to those previously proposed, which stemmed from the interactions between nearby particles. However, it turned out a concentration reversal within a single particle could not be explained by existing theories, but rather, it arises from a different mechanism. Simulations were critical in this work because, without them, we would have made an incorrect conclusion.”