Research Uncovers Silicon-Air Battery That Runs More than 1,000 Hours

Researchers have been working on a number of alternative chemistries to lithium-ion for next-generation batteries, silicon-air among them. However, while the technology has been viewed as promising and cost-effective, to date researchers haven't managed to develop a battery of this chemistry with a viable running time.

That's until now, with the invention by researchers in Germany of a silicon-air battery that can run more than 1,000 hours. Key to the development is that the team from the Institute of Energy and Climate Research (IEK) at the institute Forschungszentrum Julich discovered why in the past silicon-air batteries haven't achieved running times that are needed for use in commercial batteries.

The industry sees silicon-air batteries as good alternatives to lithium-ion batteries because they have a much higher energy density, are smaller and lighter, and are also more environmentally friendly. But undisputedly their most important advantage is the easy-to-obtain, plentiful, and inexpensive nature of silicon, which is the second most abundant element in the Earth's crust after oxygen.

One of the issues with this type of battery chemistry, however, has been that the flow of current stops after a relatively short period of time, according to researchers. To figure out why, engineers have made assumptions about various components -- including the silicon anode, the electrolyte, and the air electrode -- that have in experiments shown to be mostly untrue.

So far, the only method to keep the current flowing longer has been to use a special, high-quality electrolyte based on an ionic liquid, researchers said. This improved the battery's running time to several hundred hours, but undermined the aim of a silicon-air chemistry to provide a cost-effective alternative to lithium-ion, they said.

Julich researchers took a different approach, eyeing the consumption of the electrolyte as the source of the problem. They developed a pump system in which the electrolyte fluid, which is potassium hydroxide dissolved in water, was refilled from time to time, said Hermann Tempel, a researcher from the IEK's Fundamental Electrochemistry group.

"If the silicon anode remains in contact with the electrolyte, the battery will continue running," he said. "Until the silicon is fully used up, the battery can subsequently be recharged by exchanging the anode, in other words, mechanically."

Using this pump, researchers achieved a running time of more than 1,100 hours, or nearly 46 days, Tempel added. Now the challenge of the team is to find a way to keep the battery running without having to refill the electrolyte, he said.

"We need to stop the battery from self-discharging," Tempel said. One solution might be to add materials to the electrolyte, but the team will likely find out in future experiments. "The battery is not yet perfect, but we now know what we have to work on," he said.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 15 years. She has lived and worked as a professional journalist in Phoenix, San Francisco, and New York City. In her free time she enjoys surfing, traveling, music, yoga, and cooking. She currently resides in a village on the southwest coast of Portugal.

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