Wearables could shun batteries for sweat power

The new type of flexible supercapacitor can be used to replace the electrolytes found in conventional batteries with sweat.

It can be fully charged with as little as 20 microlitres of fluid and is robust enough to survive 4,000 cycles of the types of flexes and bends it might encounter in real-world use.

It works by coating polyester cellulose cloth in a thin layer of a special polymer. The team chose the polyester cellulose cloth because it is particularly absorbent, and the polymer offers a useful combination of flexibility, high conductivity and environmental friendliness while acting as the supercapacitor’s electrode.

As the cloth absorbs its wearer’s sweat, the positive and negative ions in the sweat interact with the polymer’s surface, creating an electrochemical reaction that generates energy.

The researchers tested the effectiveness of their tech by having volunteers run outdoors and on a treadmill while wearing a 2cm x 2cm cell version of the device. The runners sweated enough to allow the device to generate about 10 milliwatts of power – enough to power a small bank of LEDs – which kept it going until the runner stopped.

The research was led by Professor Ravinder Dahiya, head of the BEST group, based at the University of Glasgow’s James Watt School, of Engineering.

Prof Dahiya said: “Conventional batteries are cheaper and more plentiful than ever before, but they are often built using unsustainable materials which are harmful to the environment. That makes them challenging to dispose of safely, and potentially harmful in wearable devices, where a broken battery could spill toxic fluids onto skin.

“What we’ve been able to do for the first time is show that human sweat provides a real opportunity to do away with those toxic materials entirely, with excellent charging and discharging performance.

“As wearable devices like health monitors continue to increase in popularity, it opens up the possibility of a safer, more environmentally-friendly method of generating sustainable power – not just for wearables but possibly also for emerging areas such as e-bikes and electric vehicles, where sweat equivalent solution could replace the human sweat.”

Professor Dahiya and his team have developed a number of novel bendable technologies, including solar-powered ‘electronic skin’ which could be used in prosthetics and robotics. They are planning future research on the possibility of integrating sweat power into these devices.