Concrete, after water, is the world's most used material. Because it already surrounds us in the built environment, researchers have been exploring the idea of using concrete to store electricity—essentially making buildings that act as giant batteries. The idea is gaining ground as many places come to increasingly rely on renewable energy from the wind and sun. Rechargeable batteries are necessary when winds die down or darkness falls, but they are often made of toxic substances that are far from environmentally friendly.

Experimental concrete batteries have managed to hold only a small fraction of what a traditional battery does. But one team describes in the journal Buildings a rechargeable prototype material that could offer a more than 10-fold increase in stored charge, compared with earlier attempts.

A concrete battery that houses humans might sound unlikely. Still, “you can make a battery out of a potato,” notes Aimee Byrne, a structural engineer at Technological University Dublin, who was not involved in the new study. In a future where sustainability is key, she likes the idea of buildings that avoid waste by providing shelter and powering electronics.

“This is adding extra functions to the current building material, which is quite promising in my view,” says study co-author Emma Zhang, who worked on the new battery design at Chalmers University of Technology in Sweden and is now a senior development scientist at technology company Delta of Sweden. She and her colleagues mimicked the design of simple but long-lasting Edison batteries, in which an electrolyte solution carries ions between positively charged nickel plates and negatively charged iron ones, creating an electrical potential that produces voltage. In this case, conductive carbon fibers mixed into cement (a main ingredient of concrete) substitute for the electrolyte. The researchers embedded layers of a carbon-fiber mesh, coated in nickel or iron, to act as the plates.

This setup proved capable of discharging power and then recharging. “The fact that they've managed to recharge it to some degree, I think that is a very important step to where we need to be,” Byrne says. Like its inspiration, the prototype is long-lasting—Edison batteries can operate for decades—and it resists overcharging, Zhang adds: “You can abuse this battery as much as you want without jeopardizing the performance.”

Although the new design stores more than 10 times as much power as earlier attempts, it still has a long way to go: 200 square meters of the concrete “can provide about 8 percent of the daily electricity consumption” of a typical U.S. home, Zhang says.

This contribution is not enough to compete with today's rechargeable devices. “We're getting milliamps out of [cement-based batteries]—we're not getting amps,” Byrne says. “We're getting hours as opposed to days of charge.” She adds, however, that “cement-based batteries are completely in their infancy compared with other battery designs.

The earliest batteries, including Thomas Edison's, were simple and bulky. Researchers experimented with new materials and designs for more than a century to develop today's small, efficient devices. Byrne suggests concrete-based energy storage could undergo a similar evolution. “The whole idea is that we're looking far into the future,” she says. “We're playing the long game.”