Scientists develop a unique stretchable battery powered by sweat

Researchers at Nanyang Technological University, Singapore (NTU Singapore) have created an innovative soft and stretchable battery powered by human sweat.

The prototype for this novel sweat-powered stretchable battery is composed of silver flake electrodes that can generate electricity when sweat is present. The battery is miniscule, measuring a mere 2cm by 2cm, and is fastened to a bendable and sweat-absorbent textile that is stretchy and can be attached to wearable devices, such as watches, wrist bands, and arm straps.

The study has been published in Science Advances. A patent application for the sweat-powered battery has been filed through NTU’s enterprise and innovation company, NTUitive.

Testing the battery

In order to show its possible use when utilised in wearable biosensors and other electronic devices, the researchers trialled the technology using artificial perspiration.

In a different test, the group were able to show that a person equipped with the battery on their wrist and cycling on an exercise bike for 30 minutes was capable of generating a voltage of 4.2V and output power of 3.9mW that was enough to power a commercial temperature sensor device and send the data continuously to a smartphone via Bluetooth.

Sustainable alternative to traditional batteries

Standing apart from most conventional batteries, this stretchable battery does not include any heavy metals or toxic chemicals and is not composed of unsustainable materials that harm the environment. Therefore, this battery could be utilised as a more sustainable battery capable of cutting down on harmful electronic waste.

The study lead, Materials Scientist Professor Lee Pooi See, and Dean of NTU Graduate College, commented: “Our technology heralds a previously unreachable milestone in the design of wearable devices. By capitalising on a ubiquitous product, perspiration, we could be looking at a more environmentally-friendly way of powering wearable devices that does not rely on conventional batteries. It is a near-guaranteed source of energy produced by our bodies. We expect the battery to be capable of powering all sorts of wearable devices.”

The study’s co-author, Dr Lyu Jian, a Research Fellow from NTU’s School of Materials Science and Engineering, explained: “Conventional batteries are cheaper and more common than ever, but they are often built using unsustainable materials which are harmful to the environment. They are also potentially harmful in wearable devices, where a broken battery could spill toxic fluids onto human skin. Our device could provide a real opportunity to do away with those toxic materials entirely.”

Associate Professor Irene Goldthorpe from the Department of Electrical and Computer Engineering department of the University of Waterloo, Canada, who is not involved in the research, added: “It is well known that electronics do not like moisture and thus wearable devices are typically fully encapsulated to shield them from sweat. This work turns sweat from a hindrance into an asset, showing that it can improve the conductivity of printed interconnects and even using sweat as an electrolyte in a wearable, bendable battery. This may open a new paradigm in the design of wearable electronics.”

Redefining battery power

The sweat-powered battery has been developed by printing ink that comprises silver flakes and hydrophilic poly(urethane-acrylate), which serve as the battery electrodes, onto a stretchable textile. When the silver flakes make contact with sweat, its chloride ions and acidity lead to the flakes clumping together, thus enhancing their capacity to conduct electricity effectively. This chemical reaction also results in an electric current to flow between the electrodes.

When the battery material is stretched out, its resistance is further lowered, signifying that it can be employed when it is exposed to straining situations like when its user is exercising.

As the stretchable textile is incredibly absorbent, it maintains a lot of sweat, so that the battery stays powered even when the rate of sweating is not consistent. This is significant for reliable functioning as the amount of human sweat produced varies and depends on the area of the body it is in, the environmental conditions and the time of day.

Professor Lee concluded: “Our device could be more durable than current technology, as we showed it could withstand strain from a wearer’s daily activities, and repeated exposure to stress or sweat.

“The slim size of our battery also solves two problems in wearable tech: traditional button batteries are a problem for achieving the sort of sleek aesthetics that are attractive to consumers, while thinner batteries reduce the item’s ability to carry enough charge to last throughout the day.”

Going forward, the team plans to do more research into the effects of other components of human sweat and how factors such as body heat could impact the performance of the battery.

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