Weaving a net or fabric battery for use in seawater

Most batteries are rigid and incompatible with water. But people work and play in oceans and estuaries, and they could benefit from flexible and saltwater-safe power sources. Now, researchers report in ACS Applied Materials and Interfaces a yarn-like battery prototype that works when immersed in seawater. They knotted the rechargeable strands into a fishing net that lit up LEDs and wove a fabric that powered a timer. 

Flexible, yarn-like batteries can be knit or woven into various shapes. These stringy energy sources are lightweight and are often designed to be waterproof. But rather than avoid battery exposure to water entirely, scientists have proposed using salty water as a critical battery component: the electrolyte (a liquid that conducts electricity through ions). Yan Qiao, Zhisong Lu and colleagues previously developed a water-friendly battery made with carbon fiber and cotton yarn. This prior work used sweat from the body as the electrolyte for exercise monitors. Like sweat, seawater, which contains sodium, chloride and sulfate ions, can serve as an electrolyte. So, Qiao, Lu and a new team wanted to develop a marine version of a rechargeable, yarn-like battery that could be used to power lights on fishing nets, life jackets or mooring lines for buoys.

To create electrodes for the seawater batteries, the group treated carbon fiber bundles with electrically conductive coatings: nickel hexacyanoferrate for the positive electrode (cathode) and polyamide for the negative electrode (anode). Then researchers twisted two bundles together to form yarn-like cathode and anode strings. To prepare a battery, the researchers wrapped the cathode string in a layer of fiberglass, laid it along the anode, and encased both strands in a nonwoven, permeable fabric. The fabric protects the electrodes while also allowing in seawater to contact the electrodes. In tests using saltwater, the battery continued to store an electrical charge after being bent 4000 times. Then, when evaluated in seawater, it retained most of the initial charging efficiency and storage capacity over 200 charge and discharge cycles.

Finally, as a proof-of-concept, the group knotted battery strands together into a fishing net and wove a rectangular piece of fabric. The net was then soaked in seawater to absorb the electrolyte and was charged. The net battery lit up a 10-LED panel. Similarly, the fabric submerged in a sodium sulfate solution powered a timer for more than an hour. The researchers say their yarn-like battery has potential as an energy source in marine applications.

The authors acknowledge funding from the Chongqing Natural Science Foundation, the Sichuan Science and Technology Program, the Innovation Research 2035 Pilot Plan of Southwest University, and the Science and Technology Innovation Program of General Administration of Sport of China.

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