Graphene fibre cathode for smart clothes
Researchers in the US have made a graphene battery cathode in the shape of a fibre in a a zinc-ion battery prototype that could be integrated into clothing.
“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. “In this study, we created a yarn-shaped cathode. Our findings were pretty promising for such a short strip of fibre, and we hope to continue this work to improve the performance, safety, and mechanical properties of our designs.”
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The team created different manganese dioxide microparticles in various shapes and sizes. Then they used a solution-spinning process to form the fibre made of graphene oxide, with embedded manganese dioxide particles.
“Since we are trying to make a fibre-shaped zinc-ion battery, we care not only about the battery performance, but also about the mechanical properties – we need the fibre to be strong, and also flexible,” said Gao.
Researchers found the shape of the graphene oxide and manganese dioxide materials that they used to make the cathode affected its electrochemical function. Specifically, they found the shorter, rod-shaped manganese dioxide components mixed homogeneously with the graphene, allowing researchers to make a fibre that could operate as a functional battery prototype. Comparatively, they found that when the manganese dioxide had a “sea urchin” shape, the fibre couldn’t be used in a functional battery.
The electrochemical output depends on the annealing temperature and the MnO2 distribution within the fibre cathodes, while the best performer shows stable cycling stability at a maximum capacity of 80 mAh/g.
“When the graphene and manganese dioxide were well-mixed, you can use the fibre to create a functional battery,” said 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 fibre, 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 fibre.”
“This study shows that the shape and size of the additives in the fibre affected the fibre 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.”
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