How Scientists Turned Junkyard Scrap Metal Into A Battery

Inspired by an archaeological find, researchers have built a pill-bottle-sized battery starting from junkyard scrap metal. The scientists say their approach could someday be used to repurpose metal alloys commonly found around the house for energy storage applications.

Prototype battery made from scrap brass and steel. (Credit: Daniel Dubois / Vanderbilt University)

As renewable energy sources like solar become a bigger part of our energy picture, the question of how to reliably store power for that proverbial rainy day becomes more and more important. Researchers are working on plenty of different battery technologies. (I’ve written about another technology, flow batteries, in a prior post.) At Vanderbilt University, Cary Pint wondered whether he could build a battery by starting with waste.

Citing a report from the U.S. Geological Survey, Pint’s research team notes that each year, roughly 17.5 million tons of steel and 1.15 million tons of brass are not recycled and end up destined for junkyards.

Each year the U.S. produces hundreds of millions of tons of metal scrap like this, which was photographed at the PSC Metals scrapyard in Nashville. (Credit: Daniel Dubois / Vanderbilt University)

They say one man’s trash is another man’s treasure. In this case, seeing the treasure takes a little chemistry knowledge. Steel is an alloy of iron and other elements, mostly carbon. Brass is an alloy of copper and zinc. It so happens that an artifact called the “Baghdad Battery,” which approximately dates to the first century BC, consists of nothing but a terra-cotta pot, an iron rod and a copper sheet. Archaeologists consider the battery interpretation of these artifacts highly controversial. Still, their simple design was enough to inspire Pint and his team at Vanderbilt.

Pint’s team took steel and brass scraps, including screws, pipe and metal shavings, and used a chemical process called anodization to transform them into usable battery materials. (If you’ve heard of anodization, it’s likely you’ve heard about it in the context of aluminum metal— the process is frequently used to give aluminum a durable, decorative oxide finish.)

Pint’s team anodized scrap steel to obtain iron oxides, which developed on the steel surface in the shape of nano-sized rods. Anodizing brass gave the team copper oxides, which developed on the brass surface looking like nano-sized thorns. The team then placed their anodized metals into a glass jar, and added a solution of potassium hydroxide to construct a working battery.

So, how well did the the battery work? According to results published in the American Chemical Society journal ACS Energy Letters, the scrap metal battery delivers a burst of energy quickly. In technical parlance, that means the battery has a high power density. (Think of power density as “how fast you can get the energy out of the battery.”)

Why might high power density be important? When would you need a burst of energy in a hurry? Well, the flash in a digital camera needs a burst of energy. So, too, does accelerating an electric car or bus. (In China, some hybrid buses have used an energy storage technology called a supercapacitor that works this way. It quickly charges when the bus brakes, then quickly releases its energy when the driver hits the accelerator.)