Researchers look at the big picture to understand battery electrode failure

As part of an international study, researchers at Virginia Tech have helped to piece together the broadest understanding of what happens during battery electrode failure. Feng Lin, an assistant professor of chemistry in the College of Science at Virginia Tech and an affiliated faculty member of the Macromolecules Innovation Institute, led efforts, together with researchers at SLAC National Accelerator Laboratory, Purdue University and the European Synchrotron Radiation Facility in France.

Lin and his collaborators wanted to understand and quantitatively define what happens inside a battery electrode that leads to the failure of lithium-ion batteries. Up to this point, studies had zoomed in on individual areas or particles in the cathode during failure. But now Lin's study provides the first macro view to complement the existing micro studies in the battery literature. The findings are reported in a paper in Advanced Energy Materials.

"If you have a perfect electrode, every single particle should behave in the same fashion," Lin said. "But battery electrodes are very heterogeneous. We have millions, if not billions, of particles. There's no way to ensure each particle behaves at the same time."

The research team relied heavily on the synchrotron X-ray method to produce results. Synchrotrons are massive, ovoid-shaped facilities that accelerate electrons through a ring close to the speed of light. This produces ‘synchrotron X-rays’ that can be used to study materials and batteries in great detail.

Lin estimates that half of the study results came from the European Synchrotron Radiation Facility in Grenoble, France. The US Department of Energy's SLAC National Accelerator Laboratory and Brookhaven National Laboratory in the US assisted with the results, but the facility in France allowed Lin to study larger quantities of battery particles at higher resolutions.

"We were excited that we could study these many particles at once," said Yijin Liu, a scientist at SLAC. "Imaging individual active battery particles has been the focus of this field."

Lin and his Virginia Tech lab contributed to the collaboration by manufacturing materials and batteries, testing their performance, and performing experiments at the synchrotron facilities. The synchrotron facilities captured images at variously tuned settings, led by SLAC, and researchers at Purdue provided computational modeling.

Lin uses several food analogies to explain the dynamics inside a battery, such as imagining individual active battery particles like individual rice grains in a pot.

"It's impossible to have every single grain of rice identical in terms of their shapes and how far away it is to its neighbor," Lin said. "To make a better battery, you need to maximize the contribution from each individual particle. Certainly, we are excited that we have now established the battery electrode chemistry all the way from the atomic scale to the many-particle electrode scale"

Although problems such as individual particle inefficiencies have been identified, finding a solution has proved challenging for battery developers. Batteries are composed of many different parts that behave differently. Solid polymer helps hold particles together, carbon additives provide electrical connections, and then there are the active battery particles storing and releasing the energy.

This heterogeneity leads to a common problem in today’s batteries. "When you're charging, the top layer charges first, and the bottom layer charges later," explained Linqin Mu, a postdoctoral researcher in Lin's Lab. "Which part would you use to tell when your charge is complete? If you use the bottom layer as your fingerprint, the top layer will be overcharged and has safety problems."

This partially explains why some consumer electronics seem to lose power at uneven rates. For example, a cell phone could drop from 100% to 70% over a short period of time due to improper charging.

Improving batteries is a tall task, but one that Lin and his lab are dedicated to. The findings from this paper will help lay the theoretical groundwork for Lin and the entire international battery research field to chip away at the many challenges that heterogeneous electrodes hold.

This story is adapted from material from Virginia Tech, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.