Ion ‘Traffic Jams’ Are to Blame for Inefficient Batteries

Research led by a chemist at Texas A&M University has unlocked a key reason why batteries are less efficient than they could be, opening to the door to new designs and materials that could create better energy storage and performance in the future.

Sarbajit Banerjee, an affiliated faculty member in the Department of Materials Science and Engineering at Texas A&M, led an international team that’s observed a "traffic jam" of ions that slows down the charging and discharging process of electrodes, representing one of the biggest reasons why lithium-ion batteries lose efficiency. By identifying and examining this slowdown in ions, researchers can figure out how to mitigate the problem and make future batteries more efficient, he said.

“Understanding what goes wrong allows us to think about how to make it right,” Banerjee told Design News in an interview. “I am hoping this will inspire research into discovering new materials and architectures.” He and the team published a paper on their findings in the journal Nature Communications.

Research led by chemist Sarbajit Banerjee at Texas A&M University has unlocked a key reason why batteries are less efficient than they could be—a traffic jam of ions that slow down the charging and discharging process. Their work opens the door to new designs and materials that could create better energy storage and performance in the future.
(Source: Texas A&M University)

Lithium-ion batteries work in what’s called a rocking-chair model, with the discharging and charging process similar to the back-and-forth motion of the chair. As the chair rocks one way, using stored energy, lithium ions move out of one electrode through the electrolyte and into the other electrode. As the chair rocks the other way—which is when the battery charges—the reverse happens, emptying the second electrode of lithium ions.

Banerjee and his team—which included collaborators from the Lawrence Berkeley National Laboratory, Binghamton University and the National Institute of Standards and Technology—used one of the world's most powerful soft X-ray microscopes, the Scanning Transmission X-ray Microscope (STXM) at the Canadian Light Source, to image a traffic jam of lithium ions chemically driven through the nanowire-based channels of a simulated battery. This allowed them to observe what happens when these jams occur to figure out ways to solve the problem.

“One of the most frustrating things about cathode materials is that we never seem to be able to obtain the full capacities one would expect from theoretical predictions,” he explained. “Our study shows that one of the reasons for this is that even within individual particles, lithium ions form specific bands and they are not readily able to equalize or equilibrate across the entire particle. In other words, we have directly observed a bottleneck to movement of the lithium ions.”

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The bottleneck appears to originate from the fact that charge gets trapped in “puddles” along the framework, Banerjee said. “In analogy to the flow of water, only when the puddles link up, can electrons flow through the entire particle,” he said. “For an effective battery, we need to move them quickly across large distances without ‘logjams.’ Bottlenecks such as seen here prevent the entire capacity of the battery from being used and also slow down the charging/discharging process.”

Banerjee said there are two ways researchers can solve this problem in batteries, either using architectures such that charge does not have to travel large distances or by coming up with entirely different materials that allow the charge to traverse faster. The team has already “identified some incredibly promising new materials” and will soon make these findings public, he added.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 15 years. She has lived and worked as a professional journalist in Phoenix, San Francisco and New York City. In her free time she enjoys surfing, traveling, music, yoga and cooking. She currently resides in a village on the southwest coast of Portugal.