Sri Narayan tests one of his new iron-air batteries, using it to power a small fan. (USC/Dietmar Quistorf)
A University of Southern California research team has developed a cheap, rechargeable battery that could be used to store energy at solar power plants for a rainy day. The air-breathing battery uses the chemical energy generated by the oxidation of iron plates that are exposed to the oxygen in the air — a process similar to rusting.

“Iron is cheap and air is free,” Sri Narayan, professor of chemistry at the USC Dornsife College of Letters, Arts and Sciences, said. As currently developed, Narayan’s batteries have the capacity to store between eight and 24 hours’ worth of energy.

Iron-air batteries have been around for decades, but the competing chemical reaction of hydrogen generation that takes place inside the battery - known as hydrolysis - sucked away about 50 percent of the battery’s energy, making it too inefficient to be useful.

Narayan and his team managed to reduce the energy loss down to 4 percent, making iron-air batteries that are about ten times more efficient than their predecessors. The team did it by adding a very small amount of bismuth sulfide into the battery, which shuts down the wasteful hydrogen generation.