The key is anodization, a common chemical treatment used to give aluminum a durable and decorative finish. When easily available waste scraps of steel and brass are anodized using a common household chemical and residential electrical current, the researchers found that the metal surfaces are restructured into nanometer-sized networks of metal oxide that can store and release energy when reacting with a water-based liquid electrolyte.
The team determined that these nanometer domains explain the fast charging behaviour as well as the battery's stability. They tested it for 5,000 consecutive charging cycles - the equivalent of over 13 years of daily charging and discharging - and found that it retained more than 90 percent of its capacity.
Unlike the lithium ion batteries used in today's Powerwall-type systems, the steel-brass batteries use non-flammable water electrolytes that contain potassium hydroxide, an inexpensive salt used in laundry detergent.
"Imagine that the tons of metal waste discarded every year could be used to provide energy storage for the renewable energy grid of the future, instead of becoming a burden for waste processing plants and the environment," said Cary Pint, assistant professor of mechanical engineering at Vanderbilt University. "When our aim was to produce the materials used in batteries from household supplies in a manner so cheaply that large-scale manufacturing facilities don't make any sense, we had to approach this differently than we normally would in the research lab."