3D imaging reveals the cycle of a lithium metal battery

Battery researchers have successfully demonstrated the promising but temperamental lithium metal battery cycle by creating real-time 3D images.

The Chalmers University of Technology team succeeded in observing how the lithium metal in the cell behaves as it charges and discharges.

The new method may contribute to batteries with higher capacity and increased safety in our future cars and devices.

“We’ve opened a new window to understand and optimise the lithium metal batteries of the future. When we can study exactly what happens to the lithium in a cell during cycling, we gain important knowledge of what affects its inner workings,” said Aleksandar Matic, professor at the Department of Physics at Chalmers and lead author of the study.

The paper, ‘Investigating microstructure evolution of lithium metal during plating and stripping via operando X-ray tomographic microscopy,’ was published in Nature Communications.

Could lithium metal batteries be the safest yet?

There are high hopes that new battery concepts, such as lithium metal batteries, will be able to replace today’s lithium-ion batteries. The goal is to develop more energy-dense and safer batteries that will take us further at a lower cost – both financially and environmentally.

Solid-state batteries, such as lithium-sulphur and lithium-oxygen batteries, are among those being held up as promising alternatives. These concepts build on the idea that the battery anode consists of lithium metal instead of the graphite in today’s batteries. Without graphite, the battery cell will be lighter, and with lithium metal as the anode, it will also be possible to use high-capacity cathode materials. This makes it possible to achieve three to five times the energy density.

However, lithium metal batteries have one substantial issue. When the battery is charged or discharged, the lithium sometimes deposits more flatly and smoothly than it should. It often forms mossy microstructures or dendrites, long needle-like structures, and parts of the deposited lithium can become isolated and inactive. Dendrites also risk reaching the other battery electrode, causing a short circuit. Therefore, it is crucial to understand when, how, and why these structures form.

“To use this technology in the next generation of batteries, we need to see how a cell is affected by factors such as current density, the choice of electrolyte and the number of cycles. Now we have a tool to do so,” commented Matthew Sadd, a researcher at Chalmers.

Observing the imagery

The experiment to observe the formation of lithium microstructures in a working cell was conducted at the Swiss Light Source outside Zurich, Switzerland. The researchers prepared a specially designed battery cell to study when lithium is deposited in real-time and in 3D, using X-ray tomographic microscopy.

Although many researchers have wanted to study lithium metal in a working cell, no one has been able to do yet, according to the team. If they succeeded, it would be a major step forward compared with analysing images after a cell has been cycled.

Lithium metal

Matic said: “It was magical when we saw with our own eyes that it worked on the first attempt. When we observed the lithium creating big structures, like huge needles. It was almost like being in a lunar landing project.

“We’ve been wanting to observe the inner workings of lithium metal batteries in real time for so long. Now we can.”

“This is a key piece of the puzzle to be able to use lithium metal batteries on a large scale”

In the near future, the team aims to test the technique on other battery concepts. They also hope that the necessary imaging technology will be available closer to home, for example, at the Swedish MAX IV lab, a national research facility for advanced X-ray experiments.

Matic said: “We’re looking forward to developing this method to take faster measurements at a higher resolution to see more detailed microstructures formed early on in the deposition process.”

He concluded: “This is a key piece of the puzzle to be able to use lithium metal batteries on a large scale and make them safe. A lot of research teams and companies are looking at the lithium metal concept for their future prototypes.”

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