Building A Safer Button Battery

A new battery coating could help prevent burns from accidental ingestion of so-called button batteries, the small disc batteries used to power such devices as watches.

Last year, more than 3,300 people ingested button batteries, including more than 2,200 children under the age of six, according to the National Poison Data System. Outcomes ranged from no health effects to death.

Button batteries cause injury by releasing a current that breaks down water in tissue, generating hydroxide ions that chemically burn the tissue. Extensive tissue damage can occur if the battery gets stuck in the esophagus.

“The battery that is implicated in the most serious cases is the 20-mm-diameter, 3-V lithium cell,” says Toby L. Litovitz, executive and medical director of the National Capital Poison Center, who is an expert on battery injuries. “One in eight children who swallow this lithium coin cell will develop a severe, life-threatening, or lethal complication.”

A new coating could ward off such damage by stopping batteries from releasing current when they aren’t in devices. To make the coating, Robert S. Langer of Massachusetts Institute of Technology, Jeffrey M. Karp of Harvard Medical School, and coworkers used an off-the-shelf material called a quantum tunneling composite (QTC), which consists of conductive metal microparticles suspended in an insulating silicone matrix (Proc. Natl. Acad. Sci. USA 2014, DOI: 10.1073/pnas.1418423111).

Current flows through the QTC only when enough pressure from the battery compartment is applied to push the microparticles close enough for charge to jump between them. The pressure needed can be changed by adjusting the stiffness of the matrix.

The researchers attached a QTC disc to the anode of 11.6-mm, 1.5-V button batteries. They covered the rest of the anode and the gasket between the anode and cathode with a layer of waterproof polymer. The resulting QTC-coated batteries can power a laser pointer as effectively as conventional batteries.

In animal studies, the QTC-coated battery caused no tissue damage.

Litovitz commends the researchers but has reservations. “They are correct that the best solution to this problem is a safer battery,” she says. But she points to several obstacles to implementing the technology, including the type of battery the MIT team used. “While we can hope that the data gathered from a 1.5-V cell will extrapolate to a 3-V cell, that remains to be demonstrated,” she says. She also points out that adding a millimeter to these thin batteries might require redesigning products, which could hinder adoption. In addition, success depends on there being a significant difference between the pressure required to hold a battery in place and the pressure experienced in the esophagus. With the larger coin batteries, the pressure difference may not be as great as the researchers have estimated for the smaller batteries, she says.

Nevertheless, Langer and Karp are optimistic. Because the batteries aren’t medical devices, they think that clinical trials will not be necessary. They are looking for partners to produce QTC-coated batteries. They may need to change the coating composition or thickness to make it compatible with manufacturing practices, Karp says. “We don’t think cost will be an issue. We think it will add maybe pennies, definitely not dollars, to the system,” he adds.