In recent years, lithium-ion batteries have become the gold standard for powering a plethora of devices with a convenient, energy-dense unit. Lots of research is taking place to further improve li-ion batteries to make them even more efficient, stable, smaller, and cheaper. 

Washington University in St. Louis researchers are developing a battery model that replaces lithium with sodium and removes the anode, a standard battery component. The anode-free battery concept itself isn’t new, but so far these batteries haven’t proven to have a reasonable lifespan. The new research changes that.

“They always fail very quickly or have a very low capacity or require special processing of the current collector,” Peng Bai, assistant professor in the Washington University Department of Energy, Environmental & Chemical Engineering, said in a news release.

Anode-free batteries also are known for being unstable and forming dendrites — finger-like structures that grow over time and cause battery shorts or quick degradation. The composition of the new battery prevents dendrite formation.

Usually, scientists have to open up a battery after it fails to figure out what went wrong. But making observations afterward isn’t as effective as observing in-progress operations. Bai developed a unique tool that allows real-time views of battery performance to quickly spot potential instability and dendrite growth. The scientists determined that a lot of the stability boils down to how much water is in the electrolyte liquid that the ions move through in these batteries.

“We could clearly see that if you don’t have good quality control of your electrolyte, you’ll see various instabilities, including the formation of dendrites,” Bai said. “Water content must be lower than 10 parts per million.”

This research resulted in the production of a working anode-free sodium battery that has the same energy density as a traditional li-ion version but is smaller and cheaper. These batteries also use a more common metal — copper. This reduces concerns about mining the rare element lithium, which is becoming in shorter supply as demand for batteries booms.