New window into problems with lithium batteries

Michigan have found a new way of observing a phenomenon that can be problematic to next-generation lithium batteries.

The researchers at the University of Michigan have fashioned an aperture in a battery to observe the growth of dendrites, which are whiskers of lithium that grow inside batteries and can cause fires.

Lithium sulphur and lithium air batteries — which are sometimes referred to as lithium metal batteries due to their all-metal electrodes — have the potential to store 10 times more energy in the same space as current lithium ion batteries.

However, their all-metal electrodes are prone to forming dendrites, which reduce a battery's performance, raise safety concerns and cut short its lifetime.

While dendrites are widely known to be a problem in lithium metal batteries, which aren't yet on the market, their role in causing problems in current commercially available lithium ion batteries is less understood.

"As researchers try to cram more and more energy in the same amount of space, morphology problems like dendrites become major challenges. While we don't fully know why the Note 7s exploded, dendrites make bad things like that happen," said Kevin Wood, a postdoctoral researcher in mechanical engineering who helped develop the battery window.

Previous observation techniques have focused on electrochemical measurements while the battery runs. Then, analyses of the batteries after the experiment finishes reveal what physical changes occurred inside. With this approach, researchers can see the dendrites, but cannot see how they'd grown.

To observe dendrites forming, a group led by Neil Dasgupta, U-M assistant professor of mechanical engineering, mounted the so-called window-battery on a high-definition video microscope and monitored the dendrite growth and the voltage between the two electrodes, which changes during charge and discharge cycles. By doing so, they tied their observations of the electrode - whether dendrites grew or shrunk, and the general state of degradation - with the voltage measurements. They then linked the voltage patterns to specific dendrite activity.

The device helped the team ascertain why dendrites grow within next-gen lithium metal batteries. They studied a battery with two lithium electrodes to avoid complicating the problem with a different electrode that would develop its own problems.

"Our window battery is a simple platform that can be used by researchers worldwide," Dasgupta said in a statement. "It can be reproduced in any lab with an optical microscope, simple electrochemical equipment, a machine shop and a $100 budget."

A paper on the findings titled, "Dendrites and pits: untangling the complex behavior of lithium metal anodes through operando video microscopy" is published in ACS Central Science.