Dendrites Are Major Issue for Next-Generation Lithium Batteries

Dendrites are whiskers of lithium that grow inside batteries, and they can cause fires like those in the Samsung Galaxy Note 7. They are considered a major issue for next-generation lithium batteries.

A group of researchers from the University of Michigan have observed the dendrites that usually grow under cover of darkness in a closed cell by cutting a window in a battery and filming them. Instead of using the lithium ion battery utilized in consumer electronics and commercial cell phones, researchers used a next-generation lithium metal battery to perform this study.  

This study is expected to help researchers to safely elevate the applications of lithium batteries to the next level.

Lithium sulfur and lithium air batteries, which are often called lithium metal batteries as they possess all-metal electrodes, have the ability to store 10 times more energy in the same space as the current state-of-the-art lithium ion batteries.

However, the all-metal electrodes integrated in the advanced battery versions are susceptible to forming dendrites. Dendrites tend to drastically decrease a battery’s performance, reduce its lifetime and also raise safety concerns.

Nobody wants to buy an electric vehicle that decreases from 300 to 100 miles per charge after a few uses.

Neil Dasgupta, Assistant Professor, University of Michigan

One of the worst properties of dendrites is that, they can pierce in through the membrane between the electrodes and cause the battery to short out. This could even lead to spontaneous combustion of electric vehicles.

Lithium metal batteries have still not entered the market, and while the dendrites within them are known to be an issue, their role within the commercially available lithium ion batteries is not as clear.

Researchers are yet to diagnose the reason for the Samsung's phones to malfunction and this led the company to recall the product from the market. However, few researchers suspect dendrites to be the reason.

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, If we want high energy density batteries in the future and don't want them to explode, we need to solve the dendrite problem.

Kevin Wood, Postdoctoral Researcherm University of Michigan

Dasgupta and Wood are pursuing a better technique to study the real problem happening within the batteries. The techniques used most often focuses on the electrochemical measurements when the battery is functioning. The autopsies of the batteries after completing the experiment helped to study the physical changes that took place inside the battery. Although researchers can easily see the dendrites with this approach, they will not be able to see how they have grown.

Dasgupta and his team of researchers have now mounted the window-battery on a high-definition video microscope and have wired it so they can track the voltage between the two electrodes that changes during the charge and discharge cycles and also to trace the dendrite growth.

With this technique researchers collaborated the observations of the electrode, irrespective of whether the dendrites grew or shrunk, and the general state of degradation; together with the voltage measurements. Later, the researchers linked the voltage patterns to selective dendrite activity.

This device helped the researchers to accurately note down the reason for dendrites growth within next-generation lithium metal batteries. To avoid complicating the problem with a different electrode that can help in developing its own problems, researchers studied a battery with two lithium electrodes.

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

Neil Dasgupta, Assistant Professor, University of Michigan

Researchers noticed that dendrites grew as lithium accumulated on the surface of an electrode, and shrank when the reverse cycle took place. This led to lithium being pulled away from the surface.

When the lithium was removed, researchers noticed pits in the electrode. They also noticed that these pits became nucleation sites for dendrites during the next cycle.

The lithium dendrites seemed to be strangely organic, for instance, they appeared like a plant growing and then withering over the course of a battery’s cycle. Some dendrites broke off and became “dead lithium” that floated around in the battery.

The researchers discovered that not all dendrites lead to serious destruction. Wood said that, if the dendrites are small and evenly cover the surface of the electrode, then more lithium remains in play. In such cases, the performance of batteries remains stable.

If you want to get to practical operating conditions, I don't think there's any way to truly prevent dendrite growth, but by controlling dendrite growth you can enable batteries that have long lifetimes and better safety.

Kevin Wood, Postdoctoral Researcherm University of Michigan

Researchers used this insight to discover a technique to significantly increase the lifetime of lithium electrodes. This technique is expected to be revealed in a future publication.

ACS Central Science has published a paper on the findings titled, "Dendrites and pits: untangling the complex behavior of lithium metal anodes through operando video microscopy". The work was supported by the Department of Energy's Joint Center for Energy Storage Research, Pacific Northwest National Laboratory and the National Science Foundation.

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