One day, donning a T-shirt could mean you're also sporting a smart device charger. Engineers have successfully transformed cotton into a flexible, highly conductive component, which means it could charge devices.
"In the future, you can imagine our cell phones will be just like a piece of paper you can roll up. But we need to have a flexible energy device to integrate with flexible, stretchable motherboards," said Xiaodong Li, a mechanical engineering professor at the University of South Carolina who led the development with postdoc Lihong Bao. Their article was just published in the journal Advanced Materials ( abstract ).
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Li knows how to be creative with cotton T-shirts. In 2010, he and his colleagues converted one into lightweight body armor by converting the fabric into boron carbide nanowires. So when he began looking for a backbone to make a flexible energy storage device, he turned to a $5 cotton tee from Wal-Mart.
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The engineers had to make the cotton highly conductive so they tried several "recipes," Li said. He compared their experiments with trying to replicate a restaurant meal at home without having seen the chef's preparations. First they dipped the cotton in a sodium fluoride solution for an hour, took the wet material and dried it in a preheated oven for three hours. Then they heated it in a hotter furnace for an hour.
By the time it was done, the cotton had changed into activated carbon. Despite being baked, the charred-looking material could still be folded. From there, the engineers coated it with a nano-layer of the conductive metal manganese oxide for the last stage of building their energy storage device. The device, called a super capacitor, is able to respond more quickly than a battery to power needs.
Lead researcher Xiaodong Li said his team knew that future body armor would need a flexible power source. And because the scientists work in South Carolina, which used to have a big cotton industry, they thought, 'Why not use a cotton T-shirt as the energy device?'
-- Li on his A-Ha! Moment
Although others have used cotton in devices, Li said that to the best of his knowledge his research group is the first to activate a cotton T-shirt and build it into a super capacitor. Their device's performance is on par with other carbon-based super capacitors, according to their testing. After 1,000 cycles it had 97.3 percent retention.
"This is a very simple low-cost process, and it's green," Li said. In addition to starting with a renewable plant-based material, he and his research group estimate that using cotton directly from textile mills could be as much as 10 times cheaper than chemically processing coal or petroleum into activated carbon.
To take his concept to market, the process needs to be scaled up. Li said that for this next phase, he's looking for a potential industry partner. He's also reaching out to state government leaders about using this process to help revive local textile production.
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Reza Shahbazian-Yassar is an associate professor of mechanical engineering at Michigan Technological University who specializes in the application of nanomaterials for different forms of energy storage. He's familiar with the recent Advanced Materials journal article.
"The novelty of this work is that they have converted the fabric using simple heat treatment processes and a little bit of a chemical process," he said. Shahbazian-Yassar sees an advantage in clothing that contains convenient energy storage. Soldiers on the battlefield could use it in military applications, he added.
"The challenge of course is to improve the amount of energy that these fibers can store," he said. The material also has to be able to keep performing well after regular folding and stretching.
Li, who was recently in Beijing to give a presentation, said he envisions a time when academic conference attendees use roll-up electronic posters that include flexible power sources.
"I like to think about the big picture," he said. "Down the road, we will see such cotton-enabled energy devices in the market. We won't need to rely on oil any more."