Stretchable, washable batteries designed for wearables

Researchers from The University of British Columbia (UBC) have created a battery that is both flexible and washable, meaning it works even when twisted or stretched to twice its normal length, or after being tossed in the laundry. The battery is described in the journal Advanced Energy Materials.

“Wearable electronics are a big market and stretchable batteries are essential to their development,” said Dr Ngoc Tan Nguyen, a postdoctoral fellow at UBC. “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.”

The battery developed by Dr Nguyen and colleagues offers a number of engineering advances. In normal batteries, the internal layers are hard materials encased in a rigid exterior. The UBC team made the key compounds — in this case, zinc and manganese dioxide — stretchable by grinding them into small pieces and then embedding them in a rubbery plastic, or polymer. The battery comprises several ultrathin layers of these polymers wrapped inside a casing of the same polymer. This construction creates an airtight, waterproof seal that ensures the integrity of the battery through repeated use.

PhD student Bahar Iranpour suggested throwing the battery in the laundry to test its seal; so far, the battery has withstood 39 wash cycles and the team expects to further improve its durability as they continue to develop the technology. The choice of zinc and manganese dioxide chemistry also confers another important advantage, with Dr Nguyen explaining, “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.”

Work is underway to increase the battery’s power output and cycle life, but already the innovation has attracted commercial interest. The researchers believe that when the new battery is ready for consumers, it could cost the same as an ordinary rechargeable battery.

“The materials used are incredibly low cost, so if this is made in large numbers, it will be cheap,” said Dr John Madden, who supervised the work. In addition to watches and patches for measuring vital signs, the battery might also be integrated with clothing that can actively change colour or temperature.

“Wearable devices need power,” Dr Madden said. “By creating a cell that is soft, stretchable and washable, we are making wearable power comfortable and convenient.”

Image credit: Kai Jacobson/UBC.

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