Researchers from Nanyang Technological University (Singapore) have recently demonstrated a new wearable battery powered by sweat and flexibility. What challenges does powering wearable devices present, what did the researchers develop, and how does it compare to other technologies?

What challenges does powering wearable devices present?

The development of wearable electronic devices is still in its infancy, and it will not face any significant changes until flexible electronics can be solved. This is because current wearable electronics are large and bulky, making them uncomfortable to wear. Flexible electronics will create devices that can be worn like clothing, and clothing-like devices will be the key to success in wearable electronics.

However, the development of wearable devices will also be dependent on what technology powers them. To date, the only viable power solution for wearable devices is batteries, and while these can hold substantial amounts of charge, they require charging and can be heavy. Wireless energy systems could also be deployed, but they would require the user have a portable wireless energy generator on their person who defeats the purpose of a wearable device.

One solution is a wearable generator powered by something found on or in the human body. For example, some researchers are looking towards using sugar found in blood to power electrochemical generators. Other researchers are looking towards sweat with one team, which has achieved this with promising results. However, these concepts have to be wearable and flexible to be truly practical for any wearable device.

Researchers develop wearable sweat-powered battery

Researchers from Nanyang Technological University, Singapore (NTU Singapore) have recently developed a new battery that utilises human sweat as its energy source. While another team has developed a sweat-powered generator using an enzyme, the researchers in Singapore have utilised silver flake electrodes printed onto a flexible membrane. According to the researchers, the chlorine ions in sweat causes the silver flakes to clump together, generating an electrical current.

The new battery is also stretchable, making it ideal for use in wearable applications, and the system was demonstrated by integrating the battery into a worn textile. The battery, which measures just 2cm x 2cm, was demonstrated to have generated 4.2V with a power output of 3.9mW. While this may not seem like a large amount of power, it is far more than enough to power sensors and other low-energy devices.

Not only is the new battery flexible, but it is also non-toxic. This means that wearing the battery will present no harmful effects on the wearer, which must be carefully considered when designing any wearable device. Integrating the battery into a moisture absorbent material enables the battery to continue operating even if sweat production is inconsistent (essentially acting as a fuel tank).

How does it compare to other technologies?

Compared to currently available sources of power, the new sweat-powered battery is at a disadvantage even compared to the smallest LiPo batteries. Furthermore, research into solid-state batteries could see ultrathin designs overtake sweat-power designs with the ability to charge and provide large instantaneous amounts of current.

However, sweat-powered devices could find a niche in the low-powered sensor market, such as continuous glucose monitors. Because the sweat-based sensor only requires sweat to produce electricity, such sensors would not require to be charged nor integrated into a battery. Furthermore, such sensors could readily help produce sweat around the sensor by not allowing sweat to evaporate (essentially trapping any sweat produced for energy production).

Other technologies are being developed, such as those using thermocouples, but these rarely work. As the heat difference between the outer skin and air is rarely significant, the amount of energy generated by a thermocouple would be minuscule, and the sweat-powered battery produced by the Singapore team would by far be more practical.