US scientists use electron beams to grow sodium metal crystals in battery cells

Researchers in the US have discovered why sodium solid-state batteries could last longer without losing capacity, while uncovering a surprising way to grow sodium metal crystals using powerful electron beams.

The project was led by researchers at the University of Chicago, who joined forces with Argonne National Laboratory (ANL) and Thermo Fisher Scientific. They found that sodium metal can form directly from a solid electrolyte without developing a harmful chemical layer linked to battery degradation.

The team also found that electron microscopes, which are often used to examine battery materials at the atomic level, can damage the materials they are meant to study. This, the team says, could improve sodium batteries.

“Zooming in and being able to see what happens at the interfaces between battery components is an invaluable tool to diagnose what’s going wrong in our batteries and to figure out how we can heal that problem and fix it in the next generation,” James Burrow, PhD, ESRA deputy assistant director, highlighted.

Hidden battery flaws

Most modern rechargeable batteries rely on lithium-ion cells. However, lithium supplies are limited, and some batteries require critical minerals such as cobalt and copper. Sodium offers a more widely available alternative.

In 2024, the University of Chicago team developed the world’s first anode-free sodium solid-state battery. It showed promise for fast charging and long-term energy storage. To better understand its performance, they examined the solid electrolyte used in the battery with advanced electron microscopy.

Thomas Marchese, a PhD student at the University of Chicago and lead author of the study. Credit: John Zich

However, the research team realized that the powerful electron beams inside the microscope can change the structure and chemistry of sensitive battery materials, and produce misleading results. To address the challenge, they utilized advanced detectors capable of capturing detailed information with just 10 to 50 electrons per square angstrom.

Burrow said that the team used an electron beam to examine the sample. “In this process, the electrons interact with the sample and also destroy it,” he said. “This is something that’s often overlooked in the literature.”

They found out that cooling the material to extremely low temperatures did not prevent damage, unlike in previous battery studies. Instead, the team identified electrostatic charging as the main cause.

Sodium crystal formation

To the researchers’ surprise, the unexpected damage mechanism led to another important discovery. When the electron beam charged the solid electrolyte, it pushed the highly mobile sodium ions through the material.

By directing the beam at one section of the sample, the researchers were able to trigger the formation of sodium metal crystals on the opposite side. This created a fresh interface between sodium metal and the solid electrolyte, similar to what happens when an anode-free sodium battery first charges.

More importantly, the team confirmed that no reacted solid electrolyte interphase (SEI) formed between the two materials. These layers can contribute to capacity loss in conventional batteries.

“We have the proof we sought demonstrating that no reacted SEI forms between the components and is what enables this system to operate for so long without losing capacity,” Thomas Marchese, a PhD student at the University of Chicago and the study’s lead author said in a press release.

The group now hopes to study how sodium crystals grow and arrange themselves at the interface. “Next, we can study the crystallography of that sodium directly growing out of this at the interface is of great value towards better design of next-generation fuel cells,” he concluded.

Source: https://interestingengineering.com/energy/scientists-grow-sodium-metal-crystals-in-battery-cells