PNNL researcher Chongmin Wang uses an environmental transmission electron microscope to record video of bubbles inflating and deflating inside a lithium-air nanobattery. Source: PNNLLithium-air batteries are a concept battery type that contain about three times the energy capacity by weight of today’s lithium-ion batteries.

The problem is that the technology loses energy as it stores and releases its charge. Also, the battery features a reaction that hasn’t been fully explained — oxygen forming bubbles inside the battery when it discharges. The bubbles expand the battery and create wear and tear that can cause it to fail.

Researchers at the Department of Energy's Pacific Northwest National Laboratory (PNNL) have finally provided a step-by-step explanation into how lithium-air batteries form bubbles. The research shows bubbles inflating and later deflating inside a nanobattery. Previously, scientists have only been able to see bubbles but not how they were created.

“If we fully understand the bubble formation process, we could build better lithium-air batteries that create fewer bubbles,” said Chongmin Wang researcher in the Environmental Molecular Sciences Laboratory at PNNL. “The result could be more compact and stable batteries that hold onto their charge longer.”

In the video (featured above), a grey bubble pops out from the battery’s surface and grows bigger as the battery discharges. Later, it deflates, turning inside of itself.

The researchers captured the phenomenon with an in-situ environmental transmission electron microscope with a tiny battery inside its column. This allowed the researchers to watch the battery charge and discharge from the inside.

From the video evidence, researchers believe as the battery discharges, a sphere of lithium superoxide jets out from the battery’s positive electrode and becomes coated with lithium oxide. The sphere’s interior goes through a chemical reaction that forms lithium peroxide and oxygen. The oxygen gas is released and inflates the bubble, when the battery is charged it deflates like a balloon as the lithium peroxide decomposes.

The complete findings on the research can be found in the journal Nature Nanotechnology.