Inspired by a millennia-old blueprint and two of the most abundant scrap metals in the US, scientists have developed a battery prototype that could one day offer a cheap and accessible way to store renewable energy off the grid. The steel-brass battery was crafted with materials you'd find in any old junkyard and can store energy at levels approaching lead-acid car batteries, with tests showing it can withstand years worth of charging cycles to boot.
While modern batteries weren't developed until the 19th century, some believe that the seeds of the technology were planted much earlier than that. The so-called Baghdad Battery represents a set of artifacts dating back to the first century BCE, consisting of a ceramic terracotta urn, a copper sheet and an iron rod. When they were discovered in 1930, so too were traces of an acidic agent like wine or vinegar, that may have served as a battery's electrolyte.
Whether or not it was actually used as a battery is a matter of some controversy (one Mythbusters episode even tried to put the argument to bed for good), but in any case, the fact that it was possible inspired a team of researchers from Vanderbilt University to pursue a similarly simple design.
The team began with scrap brass and steel, the first and third most abundant types of metal waste in the US. The materials were then anodized using common household chemicals, a treatment typically used to give aluminum a decorative or protective oxide layer.
But in this case, the researchers found that it rearranged the surfaces of their scrap metal into nanometer-sized networks of metal oxide, which took on the ability to store and release energy when partnered with a water-based potassium hydroxide electrolyte, which has the added benefit of being non-flammable.
Putting these capabilities to the test, the team found that the battery exhibited cell voltages of up to 1.8 V, an energy density of up to 20 Wh per kilogram and a power density of up to 20 kW per kg. It also put it through 5,000 consecutive charging cycles, which is around 13 years worth of daily charging and discharging, and saw it retain more than 90 percent of its original capacity.
Rather than commercializing its invention, the team insists its objective is to make the DIY scrap-metal approach available to the masses in need of cheap ways to store energy. To that end, it is now planning to build a full-scale prototype that could be used in an energy efficient smart home and then one day, they plan to provide clear sets of instructions for others to do the same.
"We're seeing the start of a movement in contemporary society leading to a 'maker culture' where large-scale product development and manufacturing is being decentralized and scaled down to individuals or communities," says Cary Pint, assistant professor of mechanical engineering at Vanderbilt University. "So far, batteries have remained outside of this culture, but I believe we will see the day when residents will disconnect from the grid and produce their own batteries. That's the scale where battery technology began, and I think we will return there."
The team's research was published in the journal ACS Energy Letters.