Cotton that holds a charge — could this be the next big development in flexible batteries?
Flexible devices are already in development, from e-reader screens to bendy laptops. In the world of smart textiles, flexible battery systems are also part of this change — but making the full leap from the solid to fluid has remained out of our scientists’ grasps.
Perhaps not for too much longer. The journal Advanced Materials has reported a new technique, led by the University of South Carolina’s Xiaodong Li, which allows cheap, flexible fabrics to store large amounts of energy.
In the published research report, the experimental subject is a plain, cotton T-shirt. Within the following university release, Li, a professor of mechanical engineering, said:
“We wear fabric every day. One day our cotton T-shirts could have more functions; for example, a flexible energy storage device that could charge your cell phone or your iPad.”
Li developed a process that converts basic, cotton material into “highly conductive and flexible activated carbon textiles.” The fibres in the cotton are altered and made into wires and capacitors capable of storing large amounts of energy — transformed through soaking the material in flouoride and then heated in an oxygen-free environment.
Once the T-shirt was treated, dried and baked, Li’s team found the fibers were converted from cellulose to activated carbon. The oxygen-free environment prevented the material from burning or combusting during the process.
Remaining as flexible as before, by using infrared spectroscopy, the researchers discovered the carbonized material now worked as a repository for electrical current. Testing the material, small swatches were used to function as an electrode, and as a result the fibre worked well as a capacitor.
Termed “activated carbon textile”, Li reports that the material went beyond original predictons; and acts more like double-layer capacitors — also known as supercapacitors — due to the particularly high levels of energy storage possible.
However, this wasn’t enough for the team. The individual fibres were then coated with “nanoflowers” of manganese oxide. Just over a nanometre thick, these thin layers of manganese oxide enhanced the energy-storage capacities of the material even further.
“This created a stable, high-performing supercapacitor,” said Li.
According to the team, even after thousands of test charge-discharge cycles, performance didn’t diminish more than 5 percent. The T-shirts function as a pliable battery, but no longer resemble a normal, white shirt after the process, turning black as one side effect.
However, if these supercapacitors can be stacked up, there may be a future in these kinds of smart textiles - perhaps running out of battery for your smart phone while on the move may end up being a figment of the past.
Li is particularly enthusiastic about improving on the means that carbon fibres are usually created.
“Previous methods used oil or environmentally unfriendly chemicals as starting materials,” he said. “Those processes are complicated and produce harmful side products. Our method is a very inexpensive, green process.”