A battery innovation that uses the difference between body heat and air temperature to generate power may hasten the eventual arrival of self-charging smartwatches and other wearables.
The complex technology has been detailed in research from the Ulsan National Institute of Science and Technology (UNIST) in South Korea.
More electricity, less heat
The research team led by Professor Jang Sung-yeon at UNIST has created a film-like, ionic thermoelectric material which uses the temperature difference between your skin and the air around it to generate electricity.
While materials like this have been developed before, the new innovation has recorded the highest ever values — measured in ZTi, or the thermoelectric figure of merit — for an ionic thermoelectric material, recording a significant 70% increase.
With the materials running in series inside a power generation module, it generated 1.03V per 1-degrees centigrade difference in temperature. The team used the module to power an LED lightbulb, with a 1.5-degrees centigrade difference in temperature.
Perhaps more importantly, the power generated remained stable and consistently delivered 95% of its performance over a two month period, when used indoors.
Scientific challenge
Previously, it has been difficult to balance positive ions and negative ions which produce the electricity in such materials, and too many ions cause problems with the ion flow, limiting performance.
The team’s breakthrough comes in finding the right balance between positive and negative ions, and to maximize density. It’s through these design principles the team smashed the previous ZTi record.
It’s noted by DongA Science the higher the ZTi figure is, the more efficiently electricity is generated using small temperature differences. If this technology is to power future wearables, this will be a key aspect.
What does all this mean?
Professor Jang told DongA Science:
The developed material is thin and flexible, allowing it to be easily attached to the body or curved surfaces. It can be applied to the development of wearable devices like self-charging smartwatches that don’t need a battery, or self-powered sensors that can operate in environments with internal-external temperature differences of just a few to several tens of degrees Celsius
Battery life continues to be a barrier for many considering a smartwatch, where a few days use with all sensors and features active is about the most you can expect on a single charge. While solar is an option on some connected models, a traditional battery is more common.
Innovations like this, and new battery types designed for smart rings, have the potential to lower concerns over battery life, should they eventually make it to production. In-depth scientific details on the team’s ionic thermoelectric material can be found in the research paper.