“Since we are trying to make a fiber-shaped zinc-ion battery, we care not only about the battery performance, but also about the mechanical properties – we need the fiber to be strong and also flexible.”Wei Gao, North Carolina State University

Researchers at North Carolina State University (NC State) have managed to make a cathode, or the positive end of a battery, in the shape of a thread-like fiber. The researchers were then able to use this fiber to create a zinc-ion battery prototype that could power a wristwatch.

Reported in a paper in ACS Applied Materials and Interfaces, this proof-of-concept study is a step forward in the development of a fiber-shaped battery that could ultimately be integrated into garments.

“Ultimately, we want to make a yarn-shaped battery, so we could put it in a real garment, and preferably hide it,” said Wei Gao, associate professor of textile engineering, chemistry and science at NC State and corresponding author of the paper. “In this study, we created a yarn-shaped cathode. Our findings were pretty promising for such a short strip of fiber, and we hope to continue this work to improve the performance, safety and mechanical properties of our designs.”

To create the cathode, the researchers utilized the unique properties of graphene – a strong material with a high surface area and good conductivity. First, they created different manganese dioxide microparticles in various shapes and sizes. Then they used a solution-spinning process to form a fiber made of graphene oxide, into which they embedded the manganese dioxide particles. Finally, they studied the electrochemical and other properties of these fibers.

“Since we are trying to make a fiber-shaped zinc-ion battery, we care not only about the battery performance, but also about the mechanical properties – we need the fiber to be strong and also flexible,” Gao said.

The researchers found that the shape of the graphene oxide and manganese dioxide materials used to make the cathode affected its electrochemical function. Specifically, they found that shorter, rod-shaped manganese dioxide particles worked best, mixing homogeneously with the graphene and allowing them to make a fiber that could operate as a functional battery prototype. In contrast, when the manganese dioxide particles had a ‘sea urchin’ shape, the resulting fiber couldn’t be used in a functional battery.

“When the graphene and manganese dioxide were well-mixed, you can use the fiber to create a functional battery,” said the paper’s first author, Nakarin Subjalearndee, a former graduate student at NC State. “If the manganese dioxide was shaped like a sea urchin, it meant the cathode thread had a rough surface, and could not be used.”

“The rod-shaped manganese dioxide gave us the best performance,” Gao added. “These particles mimicked the configuration or geometry of the fiber, as compared to the sea urchin-shaped particles, which were round with all kinds of edges pointing out. They disturbed the stacking of the graphene oxide nanosheets within the fiber.”

Though the battery’s power-output was low, the researchers were still able to use it to power a wristwatch. The team wants to continue their work to improve the battery’s performance.

“This study shows that the shape and size of the additives in the fiber affected the fiber formation process of graphene oxide,” Gao said. “We hope to keep developing this system; we want our design to be comparable to a commercial battery.”

This story is adapted from material from North Carolina State University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.