NC State and Rice University create moisture-powered stretchable batteries

NC State and Rice University create moisture-powered stretchable batteries

Researchers from North Carolina State University and Rice University have developed a non-toxic, stretchable battery that generates power by extracting moisture from the surrounding air. The moisture-activated battery (MAB) is designed to function across various environments, including climates as dry as the desert.

Current Internet of Things (IoT) applications, such as miniature robotics and wearable monitors, require power sources that are lightweight and flexible. According to the research team, conventional batteries are often too heavy or rigid for these uses and may contain toxic materials prone to leaking. While energy harvesters are lighter, they typically suffer from limited performance.

The MAB utilizes a magnesium anode and a silver/silver chloride cathode. These components are separated by a cellulose membrane loaded with lithium chloride salts. This separator harvests ambient moisture to dissolve the salts, creating the electrolyte necessary for charge to flow.

"Our battery eliminates toxic and flammable electrolytes because it’s essentially running on salt water,"

Amay Bandodkar, assistant professor of electrical and computer engineering at NC State and co-corresponding author of the research, via news.ncsu.edu

Bandodkar noted that because the device only activates upon exposure to ambient air, it remains inactive while in sealed packaging, which extends its shelf life.

Bioinspired Design and Performance

To maintain energy density during movement, the researchers implemented a design inspired by the scales of a pangolin. Most stretchable batteries rely on serpentine interconnectors, but these often create gaps when stretched that lower energy density. The MAB uses densely packed overlapping scales to eliminate these gaps.

"Mechanics plays a central role in making these batteries both stretchable and practical,"

Raudel Avila, assistant professor of mechanical engineering at Rice University and co-corresponding author of the study, via news.ncsu.edu

Avila stated that modeling showed how this bioinspired stacking and the use of stretchable interconnectors redistribute deformation. This allows the battery to preserve performance during twisting, bending, and stretching.

In practical tests, the MAB powered a wireless Bluetooth oximeter for up to 30 hours. Rajaram Kaveti, a postdoctoral researcher at NC State and first author of the study, added that the battery is lighter than many commercial options and uses biodegradable, biocompatible materials.

According to the study abstract, the battery offers a specific energy of ~81 mWh/g, a specific capacity of ~52 mAh/g, and an open-circuit voltage of ~1.6 V.

Anti-Tampering "Kill Switch"

The team also developed a "kill switch" using the same moisture-harvesting technology to protect surveillance monitors used in covert intelligence gathering. The switch contains a dry mixture of aluminum and iodine powder in an isolated compartment covered by a moisture harvesting cellulose membrane.

If the device housing is pressured—such as during an attempt to disable or remove the gear—the dry powder makes contact with harvested water. This triggers a violent chemical reaction that destroys the device in flames.

The researchers demonstrated this by installing the switch in a MAB-powered wireless gas sensor. The device, including its embedded CMOS electronics, was obliterated within 3 minutes of activation.

Institutional Support

The study appears in Science Advances. Funding was provided by the Chancellor’s Innovation Fund and the Advanced Self-Powered Systems of Integrated Sensors and Technologies (ASSIST) Center Industry Seed Fund at NC State, as well as the ENRICH office at Rice University.

Key contributors include co-first authors Rajaram Kaveti, Akshay Bhardwaj, and Ayemeh Bagheri Hashkavayi from NC State, and Pei Liu from Rice University. Other NC State collaborators include Veena Misra, Bünyamin Şahin, Gurudatt N.G., Baha Erim Uzunoğlu, Mahaboobbatcha Aleem, Adrian Rodriguez-Kattan, and Bhavya Jain.

Abraham Vázquez-Guardado, assistant professor of electrical and computer engineering at NC State and co-corresponding author, stated the technology is ready to power a new generation of medical and IoT applications.