Researchers at Rice University are lighting up the coatings world with news of a lithium-ion battery that can be spray-painted on virtually any surface.
The rechargeable battery consists of spray-painted layers, each representing the components in a traditional battery. The research appears in the new online issue of Nature’s online, open-access journal Scientific Reports.
‘Improved Form Factor’
Researchers have filed for a patent on the technique, which could mark the beginning of the end for traditional cylindrical batteries.
Ajayan Lab / Rice University
|An electron microscope image shows the five-layer structure of a spray-painted lithium-ion battery developed at Rice University.|
“There has been 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.” said Rice materials scientist Pulickel Ajayan, who directs the lab where the research is underway.
“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.”
The battery consists of five layered components: two current collectors, a cathode, an anode and a polymer separator in the middle. The university describes each layer as an “optimized stew.”
• Layer 1, the positive current collector, is a mixture of purified single-wall carbon nanotubes with carbon black particles dispersed in N-methylpyrrolidone.
• Layer 2, the cathode, contains lithium cobalt oxide, carbon and ultrafine graphite (UFG) powder in a binder solution.
• Layer 3 is a polymer separator paint made of Kynar Flex resin, PMMA and silicon dioxide dispersed in a solvent mixture.
• Layer 4, the anode, is a mixture of lithium titanium oxide and UFG in a binder.
• Layer 5 is the negative current collector, a commercially available conductive copper paint, diluted with ethanol.
Lead author Neelam Singh, a graduate student, and her team spent painstaking hours formulating, mixing and testing paints for each of the components. The students airbrushed materials onto ceramic bathroom tiles, flexible polymers, glass, stainless steel and even a beer stein to see how well they would bond with each substrate.
In the first experiment, the university reports, nine bathroom tile-based batteries were connected in parallel. One was topped with a solar cell that converted power from a white laboratory light.
When fully charged by both the solar panel and house current, the batteries alone powered a set of light-emitting diodes that spelled out “RICE” for six hours; the batteries provided a steady 2.4 volts.
Neelam Singh / Rice University
|Conventional lithium-ion batteries wrap active layers into a canister or other portable container. But researchers have found a way to paint those layers onto any surface.|
The researchers reported that the hand-painted batteries were remarkably consistent in their capacities, within plus or minus 10 percent of the target. They were also put through 60 charge-discharge cycles with only a very small drop in capacity, Singh said.
“The hardest part was achieving mechanical stability, and the separator played a critical role,” Singh said.
“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.”
Scaling Up, Snapping Together
Singh said the batteries were easily charged with a small solar cell. She foresees the possibility of integrating paintable batteries with paintable solar cells—another material in development—to create an energy-harvesting combination.
Photos: Jeff Fitlow / Rice University
|So far, the paint-on battery can energize a beer stein (hey, it’s a grad student project) and, when painted on ceramic tile, provide six hours of illumination to a sign.|
Scaling up the hand-painted production process would improve the result, Singh said.
“Spray painting is already an industrial process, so it would be very easy to incorporate this into industry,” Singh said.
The team is now looking for electrolytes that would make it easier to create painted batteries in the open air. They also foresee their batteries made into snap-together tiles that can be configured in a number of ways.
“We really do consider this a paradigm changer,” said Singh.
Watch a video about Rice’s paintable batteries.