Accidentally swallowing a battery happens more often that you might think, especially those little button batteries for watches, calculators, and small lights. These send 4,000 kids to the emergency room a year. Not only could we choke on them, ingested batteries also permanently damage the esophagus and digestive tract when they short-circuit in our saliva and intestinal fluids. The electric current produces caustic, tissue-damaging hydroxide, which leads to a chemical burn, followed by bleeding and possibly death.
To try to prevent those injuries, researchers have now developed a waterproof, pressure-sensitive coating for batteries that still preserve their original function of powering our little devices. The battery stops conducting electricity if it’s swallowed. The work was published in Proceedings of the National Academy of Sciences this week.
Five billion button batteries are produced every year, and the more powerful they become, the more dangerous they are if swallowed. Serious tissue damage can happen within just a couple hours. Recent legislation in the U.S. requires warning labels on packages, and some toys required battery housings that must be opened with a tool. But there’s been no technological innovations to make the batteries themselves safer.
Developed by MIT’s Robert Langer, Harvard’s Jeffrey Karp, and colleagues, the new battery armor is composed of quantum tunneling composite (QTC), an off-the-shelf material commonly used in computer keyboards and touchscreens. That rubberlike silicone material is embedded with metal particles that are, under normal circumstances, too far apart to conduct an electric current. Electricity is only conducted under the high pressure of a battery housing environment. When the metal particles are squeezed to within a few nanometers of each other, the electrons burrow through the silicone through a process called quantum tunneling, Science explains, turning the composite into a conductor.
The QTC serves as an insulator in all other low-pressure environments when not being compressed. It’s attached to the battery’s anode (the positively charged electrode) with a conductive silver paste, while the rest of the anode is coated in insulating silicone.
The team also calculated how much pressure the battery would experience inside the digestive tract. “You want to know what’s the maximum force that could possibly be applied, and you want to make sure the batteries will conduct only above that threshold,” study author Bryan Laulicht of MIT says in a news release. “We felt that once we were well above those levels, these coatings would pass through the GI tract unchanged.”
When they deployed the battery in a pig's esophagus, the coated batteries inflicted no discernable tissue damage. Exposure to conventional batteries resulted in damage within just two hours. Pictured here, a typical button battery on the left and a button battery coated with QTC on the right:
Images: Christine Daniloff/MIT (top) & Bryan Laulicht (bottom)