Concrete is the world’s most consumed material after water. Because it already surrounds us in the built environment, researchers have been exploring the idea of using concrete to store electricity—essentially turning buildings into giant batteries. The idea has been gaining ground as we have come to increasingly rely on renewable energy from the wind and sun: rechargeable batteries are necessary when the breeze dies down or darkness falls, but ironically, they are often made of toxic substances that are far from environmentally friendly.
Experimental concrete batteries have only managed to hold a fraction of what a traditional battery does. But one team now reports in Buildings that it has developed a rechargeable prototype that could represent a more than 900 percent increase in stored charge, compared with earlier attempts.
A live-in concrete battery might sound unlikely. Still, “you can make a battery out of a potato,” notes Aimee Byrne, a lecturer in structural engineering 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 the 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, the researchers mixed conductive carbon fibers into cement (a main ingredient of concrete) to substitute for the electrolyte. They also embedded layers of a carbon-fiber mesh, coated in either 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 work for decades). And it resists overcharging, Zhang adds. “You can abuse this battery as much as you want without jeopardizing the performance,” she says.
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 it “can provide about 8 percent of the daily electricity consumption” of a typical U.S. home, Zhang says.
This 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.” But she adds that “cement-based batteries are completely in their infancy, compared to 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 with it.”