A hole-filled battery could make wearables more breathable than cotton

A stretchy and flexible battery pouch filled with strategically placed holes is more breathable than cotton. That could make it an ideal power source for wearable sports or fitness devices built directly into clothing.

“This is especially useful for athletes or individuals who wear electronics for extended periods – smart clothing for fitness tracking, medical monitoring devices and similar applications that demand both comfort and reliable performance,” says Lin Xu at Yale University.

To design the new battery, Xu and his colleagues created a pattern of long, rectangular holes in a pouch cell battery – a type of lithium battery that resembles a flat bundle with a limited degree of bendability. Simulations showed how the array of rectangular holes enabled the battery to be stretched or folded 180 degrees without tearing, compared with alternative hole patterns involving squares or circles.

“One challenge was maintaining enough active material to keep the battery’s energy density high – too many or too large holes would reduce the energy storage capacity,” says Xu. “We had to balance mechanical stretchability with electrical performance.”

When stretched by 10 per cent or even folded up, the holey battery design could still resist physical stress and continue to power LED light bulbs – with the stretching and folding experiments each performed 100 times. Testing in a temperature and humidity chamber also showed that the battery was twice as breathable as cotton.

As a practical demonstration of the possible uses, the researchers wove the battery into a lab coat and tested its performance while the wearer ran around exercising. Its holes enabled the battery to quickly dissipate heat so it would not feel painful or trap sweat on the wearer’s skin.

The battery still needs more wear-and-tear testing, so the researchers plan to test its performance in commercial health monitoring devices and sports gear.

They are also investigating how to best scale up production – automated manufacturing must be able to provide consistent hole placement and sealing to avoid leaks or short circuits in the battery pouch.