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Analytical theory may bring improvements to lithium-ion batteries

Researchers have shown theoretically how to control or eliminate the formation of “dendrites” that cause lithium-ion batteries to fail, an advance that if realized would improve safety and might enable the batteries to be charged within a matter of minutes instead of hours.

The dendrites are lithium deposits that form on electrode surfaces and may continue to grow until they cause an internal short circuit, which results in battery failure and possible fire.

Researchers have created an analytical theory that shows how to design experiments to study ways of controlling dendrite growth, and results of the theory allow researchers to predict early stages of dendrite formation.

“We believe that this work is the first of its kind because, prior to its publication, work on this area had heavily relied on anecdotal evidence,” said R. Edwin García, an associate professor of materials engineering at Purdue University. “While we have applied this theory to lithium-ion batteries, it was formulated so that it could be readily applied to other emerging battery chemistries, such as magnesium-ion and lithium-sulfur.”

Findings were detailed in a research paper published in February in the Journal of the Electrochemical Society. The paper was written by postdoctoral researcher David Ely and García, and the work was funded by Toyota Motor Engineering & Manufacturing North America Inc.

The dendrites are lithium formations that grow like tumors while batteries are being recharged. Some of them add layers that when cut in half reveal an internal structure like tree rings, with each layer representing a single recharge. Because they grow faster when exposed to the high voltages needed for fast recharging, the dendrites limit recharging speed.

“You want your battery to recharge as fast as possible, in a matter of 10 minutes or so,” García said. “This would be possible if we could better control or eliminate dendrite growth.”

The batteries have two electrodes, called an anode and a cathode, separated by an insulating polymer that keeps the electrodes from touching. When the battery is recharged, lithium ions are shuttled from the cathode to the anode through a liquid or gel called an electrolyte, from which the dendrites draw material to build up on the anode’s surface. The dendrites may grow large enough to penetrate the separating barrier and touch the cathode.

“The moment these touch, the battery is dead,” García said. “Or worse, if you have too much current going through the dendrites while the battery is being charged, the battery can catch fire.”
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