A battery made with urea, commonly found in fertilizers and mammal urine, could provide a low-cost way of storing energy produced through solar power or other forms of renewable energy for consumption during off hours.

Developed by Stanford chemistry Professor Hongjie Dai and doctoral candidate Michael Angell, the battery is nonflammable and contains electrodes made from abundant aluminum and graphite. Its electrolyte's main ingredient, urea, is already industrially produced by the ton for plant fertilizers.

"So essentially, what you have is a battery made with some of the cheapest and most abundant materials you can find on Earth. And it actually has good performance," said Dai. "Who would have thought you could take graphite, aluminum, urea, and actually make a battery that can cycle for a pretty long time?"

In 2015, Dai's lab was the first to make a rechargeable aluminum battery. This system charged in less than a minute and lasted thousands of charge-discharge cycles. The lab collaborated with Taiwan's Industrial Technology Research Institute (ITRI) to power a motorbike with this older version, earning Dai's group and ITRI a 2016 R&D 100 Award. However, that version of the battery had one major drawback: it involved an expensive electrolyte.

The newest version includes a urea-based electrolyte and is about 100 times cheaper than the 2015 model, with higher efficiency and a charging time of 45 minutes. It's the first time urea has been used in a battery. According to Dai, the cost difference between the two batteries is "like night and day." The team recently reported its work in the Proceedings of the National Academy of Sciences.

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