Low-cost battery for storing renewable energy
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.”
Renewable energy storage
Unlike energy derived from fossil fuels, solar energy can essentially be harnessed only when the sun is shining. A solar panel pumps energy into the electrical grid during daylight hours. If that energy isn’t consumed right away, it is lost as heat. As the demand for renewable technologies grows, so does the need for cheap, efficient batteries to store the energy for release at night. Today’s batteries, like lithium-ion or lead acid batteries, are costly and have limited lifespans.
Dai and Angell’s battery could provide a solution to the grid’s storage problem. “It’s cheap. It’s efficient. Grid storage is the main goal,” Angell said.
According to Angell, grid storage is also the most realistic goal, because of the battery’s low cost, high efficiency and long cycle life. One kind of efficiency, called Coulombic efficiency, is a measurement of how much charge exits the battery per unit of charge that it takes in during charging. The Coulombic efficiency for this battery is high—99.7 percent.