Electronics woven into fabrics promise to open up all kinds of interesting possibilities, from clothing that monitors muscle activity and tracks breathing, to garments that can talk to one another. Developing pliable power sources to go with them is an equally important field of research, and scientists at the University of British Columbia have put forward a particularly impressive solution they say could be the first ever battery that is both flexible and washable.
Over the past few years we have seen a variety of stretchable energy storage solutions designed to power wearable devices, from millimeter-scale batteries that stretch over the skin like a Band-Aid to fabric-like batteries that draw power from sweat. The University of British Columbia team has now leveraged some engineering advances to fill what they see as important gaps in the current technology.
“Wearable electronics are a big market and stretchable batteries are essential to their development,” says study author Dr. Ngoc Tan Nguyen. “However, up until now, stretchable batteries have not been washable. This is a critical addition if they are to withstand the demands of everyday use.”
To develop a battery with these capabilities, the scientists reimagined the way these devices are put together. Rather than forming a lithium-ion battery packed with hardened materials inside a rigid exterior, the team turned to an alternative chemistry in zinc and manganese dioxide, which is appealing for its low cost and safety. These materials were ground down into tiny pieces and embedded in a polymer to form ultra-thin and stretchable layers, with several of these stacked up and encased in the same polymer to seal up the finished product.
“We went with zinc-manganese because for devices worn next to the skin, it’s a safer chemistry than lithium-ion batteries, which can produce toxic compounds when they break,” says Nguyen.
The resulting battery is flexible and can be stretched to twice its normal length, has a specific capacity of 160 mAh g−1 and retains 75 percent of its capacity over 500 charge and discharge cycles. Impressively, the team found the seal worked well enough for the battery to withstand 39 wash cycles so far.
“We put our prototypes through an actual laundry cycle in both home and commercial-grade washing machines," says team member Bahar Iranpour. "They came out intact and functional and that’s how we know this battery is truly resilient."
The team is now working to improve the power output and lifetime of the battery, and says the creation has already attracted commercial interest, with the cost expected to be similar to a standard rechargeable battery. They imagine it being put to use in watches and patches that measure vital signs, and in smart clothing that does much the same thing.
“The materials used are incredibly low-cost, so if this is made in large numbers, it will be cheap,” says electrical and computer engineering professor Dr. John Madden, who supervised the work. “Wearable devices need power. By creating a cell that is soft, stretchable and washable, we are making wearable power comfortable and convenient.”
The research was published in the journal Advanced Energy Materials.
Source: University of British Columbia