June 29, 2012
Paint With Power
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Michael Harper for redOrbit.com — Your Universe Online
Researchers at Rice University in Houston, Texas have put their minds together to create an incredibly thin battery. So small, in fact, if can be painted on the surface of whatever it´s meant to power. This rechargeable lithium-ion battery is applied in layers, recreating the components of a traditional battery. Rice scientist Pulickel Ajayan helped to create the sprayable battery and posted the corresponding research in Nature´s Scientific Reports.
“This means traditional packaging for batteries has given way to a much more flexible approach that allows all kinds of new design and integration possibilities for storage devices,” said Ajayan, Rice´s Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science, in a statement.
“There has been a lot of interest in recent times in creating power sources with an improved form factor, and this is a big step forward in that direction.”
The project began with a great deal of deconstruction as lead author Neelam Singh and her team mixed and tested paints until they had recreated each of the five components found in a battery: an anode, a cathode, two current collectors, all surrounding a polymer separator. To test their power paint, the team applied the layers to 9 bathroom tiles laid out in a grid. The team then connected these tiles together, then connected the set of tiles to a series of LED lights. In the end, Alayan and team were able to power the LEDs (which spelled RICE) via bathroom tiles for 6 hours with a steady 2.4 volts of power.
The team even applied their sprayable battery to a beer stein in order to test how well the components bond to different surfaces.
According to their research, the scientists found the bathroom-tile batteries were very consistent in their capacity, within 10%, plus or minus, of their target. Even after 60 charge and discharge cycles, the batteries only experienced a slight drop in their capacity.
This sprayable battery is a delicate mixture of many elements. The bottom layer contains a positive current collector: a mixture of purified single-wall nanotubes and carbon black particles mixed in N-methylpyrrolidone. The second layer is dedicated to the cathode, which contains lithium cobalt oxide, carbon and an ultra-fine graphite powder, all held together by a binding solution. The third sprayable layer is a polymer separator. In this instance, the separator is a Kynar Flex resin, PMMA and silicon dioxide mixed in mixture of solvents. The anode layer contains a blend of lithium titanium oxide and more ultra-fine graphite powder in a binding solution. The last layer is the easiest of all, consisting of a commercially-available conductive copper paint, mixed with a little ethanol, for a kick. This layer acts as the negative current connector.
Out of the entire process, Singh said, “The hardest part was achieving mechanical stability, and the separator played a critical role.”
“We found that the nanotube and the cathode layers were sticking very well, but if the separator was not mechanically stable, they would peel off the substrate. Adding PMMA gave the right adhesion to the separator.”
Once each layer was sprayed on the surface, the battery was then infused with electrolytes, heat sealed and charged for power.
These batteries are not only slim, they´re also easy to charge. According to Singh, these power paints are easily charged by a small solar cell. Combined with the new paintable solar cells, Singh says you have a recipe for tremendous energy-harvesting.
“Spray painting is already an industrial process, so it would be very easy to incorporate this into industry,” Singh said.
Image 2 (below): Ceramic tiles coated with battery paints and then heat-sealed powered LEDs spelling out "RICE" for six hours in an experiment at Rice University. The lithium-ion batteries can be painted on virtually any surface. Credit: Jeff Fitlow/Rice University
Image 3 (below): A beer stein served as an able substrate for a paintable battery developed at Rice University. Credit: Jeff Fitlow/Rice University