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OFF THE WALL: Rice Scientists Charged up about Battery Paint

Thursday, July 5, 2012

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Walls with paintable solar cells and paintable batteries could make one hard-to-beat energy-harvesting cocktail.

That’s the latest from scientists at Rice University (Houston, Texas), who say they have developed a lithium-ion battery that can be “painted on” virtually any surface.

Jeff Fitlow/Rice University

Rice University graduate student Charudatta Galande, Professor Pulickel Ajayan and graduate student Neelam Singh show off the first test device for their paintable batteries, an array of standard ceramic tiles combined with a solar cell and an array of LEDs, which the batteries powered for six hours.

In a video detailing the invention, Neelam Singh, a Rice graduate student who led the research, said, “Ceramic tiles that become converted into batteries could be used to build entire exterior walls of a house. A wall made of these batteries could then be covered with solar cells and this combination of solar cells and batteries could be used to capture and store the solar energy into useful electricity.”

Researchers said the rechargeable battery can be created by spray-painting layers that represent each component of a traditional battery onto any surface.

The five-layered components include two current collectors, a cathode, an anode, and a polymer separator in the middle, the researchers said.

More specifically, the researchers said the first layer functions as the positive-current collector, a mixture of purified single-wall carbon nanotubes with carbon black particles dispersed in N-methylpyrrolidone. The second is the cathode, which contains lithium cobalt oxide, carbon and ultrafine graphite (UFG) powder in a binder solution.

The third layer is the polymer separator paint of Kynar Flex resin, PMMA and silicon dioxide dispersed in a solvent mixture. The fourth, the anode, is a mixture of lithium-titanium oxide and UFG in a binder, and the final layer is the negative current collector, a commercially available conductive copper paint, diluted with ethanol.

Powering up

After formulating and mixing, the scientists airbrushed the 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, 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,” the researchers reported.

The painted-on batteries were “remarkably consistent” in performance on the varying substrates, the researchers said.

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.”

In addition, Singh said she sees the “possibility of integrating paintable batteries with recently reported paintable solar cells to create an energy-harvesting combination that would be hard to beat.”

The hand-painted batteries appear to work well, Singh said, but scaling up with modern production methods will improve the technology. “Spray painting is already an industrial process, so it would be very easy to incorporate this into industry,” she said.

The researchers have filed for a patent on the technology and will continue to refine the process.

“We really do consider this a paradigm changer,” Singh said.

Elsewhere in the Lab:
Dealing with Strain

“Battery paint” isn’t the only paint scientists at Rice are dabbling in. A recent study highlights the discovery of something called “strain paint,” a coating made of carbon nanotubes that is reported to detect strain in buildings, bridges and airplanes; see: Strain Paint: Noncontact Strain Measurement Using Single-Walled Carbon Nanotube Composite Coatings.