A fabric-based 'battery of the future' that draws its energy from the moisture in the air has been developed by a research team at the NUS College of Design and Engineering (CDE).
Made from a thin layer of non-woven fabric and other, mostly everyday materials, like sea salt, the researchers say this breakthrough could pave the way to long-lasting, foldable batteries being used to power wearables and many other devices.
The moisture-driven electricity generation (MEG) battery was developed by a research team led by Assistant Professor Tan Swee Ching (Department of Materials Science and Engineering at the CDE). Their breakthrough was published recently in the scientific journal Advanced Materials.
The concept of MEG devices derives from the ability of different materials to generate electricity from interaction with moisture in the air. This has received growing interest due to its potential for a wide range of applications, including powering devices such as wearable technologies like health monitors, electronic skin sensors, as well as information storage devices.
However, the development of the technology has faced several key challenges, such as water saturation of the device when exposed to ambient humidity and unsatisfactory electrical performance.
To overcome these, the NUS team devised a novel MEG device containing two regions of different properties to perpetually maintain a difference in water content to generate electricity and allow for electrical output for hundreds of hours.
The NUS team's MEG device consists of a thin layer of fabric coated with carbon nanoparticles.
One part of this fabric is coated with a moisture-absorbing hydrogel, made using sea salt, that can absorb more than six times its original weight. The other end of the fabric is left untouched, keeping this region dry whilst the moisture is confined to the area treated with the hydrogel.
"Sea salt was chosen as the water-absorbing compound due to its non-toxic properties and its potential to provide a sustainable option for desalination plants to dispose of the generated sea salt and brine," said Asst Prof Tan.
Once the MEG device is assembled, electricity is generated when the ions of sea salt are separated as water is absorbed in the hydrogel-treated 'wet' region.
Free ions with a positive charge are absorbed by the carbon nanoparticles which are negatively charged. This causes changes to the surface of the fabric, generating an electric field across it as well as giving the fabric the ability to store electricity for use later.
"With this unique asymmetric structure, the electric performance of our MEG device is significantly improved in comparison with prior MEG technologies, thus making it possible to power many common electronic devices," said Asst Prof Tan.
Because of its fabric base, the team's MEG device is highly flexible and able to withstand stress from twisting, rolling and bending with no loss of performance.
Portable power source
The MEG device has immediate applications due to its ease of scalability and commercially available raw materials, the most promising being as a portable battery for powering electronics directly from ambient humidity.
"After water absorption, one piece of power-generating fabric 1.5x2 centimetres in size can provide up to 0.7 volts of electricity for over 150 hours under a constant environment," said research team member Dr Zhang Yaoxin.
The NUS team has also successfully demonstrated the scalability of its new device in generating electricity for different applications.
For example, by connecting three pieces of the power-generating fabric together and placing them into a 3D-printed AA battery case, the assembled device was tested to reach as high as 1.96 volts - more than enough to power small electronic devices such as an alarm clock.
"Our device shows excellent scalability at a low fabrication cost," said Asst Prof Tan.
"Compared to other MEG structures and devices, our invention is simpler and easier for scaling-up integrations and connections. We believe it holds vast promise for commercialisation."
The researchers have filed a patent for the technology and are planning to explore its use in a broad range of commercial applications.
