Spray-on Battery Technology Puts a Charge Into Energy Field

Rice researchers' refined method for spraying an energy source onto surfaces could power a revolution.

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Imagine the day you'll be able to recharge your new mobile gadgets with the clothes you're wearing or even the paint on the gadgets themselves. That day may be closer than you think.

Several years ago, researchers began to study the world of ultra-thin batteries. Researchers at Stanford University announced in the Proceedings of the National Academy of Sciences in 2009 that they'd created batteries made out of plain copier paper. The researchers used carbon nanotubes--an interconnected mesh of millions of fibers--to store energy and generate electricity.

At the time, others predicted that this sort of research could one day lead to the concept of "paintable batteries"--in essence, the ability to paint one layer of carbon nanotubes after another onto common materials that fold, bend, or curl.

Now, researchers at Rice University have taken this research a step further--and are much closer to an actual paintable battery in reality--by developing a technique in which a lithium-ion battery can be painted on virtually any surface.

The paintable battery, which could be combined with solar cells to generate power, consists of spray-painted layers that represent the components of a traditional battery. The research findings were explained in an open-access journal, Nature's Scientific Reports, earlier this summer.

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The rechargeable battery was created in the materials science lab of Pulickel Ajayan, a mechanical engineering and materials science professor at Rice, a school known for its ability to combine science and engineering to develop breakthrough, technology-based products.

"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," Ajayan said. "There has been a lot of interest in recent times in creating power sources [like paintable batteries], and this is a big step forward in that direction."

The lead author on the study is a Rice graduate student, Neelam Singh. She and her team tried all sorts of combinations for various paints representing each of five layered components: two current collectors, a cathode, an anode, and a polymer separator in the middle.

The team airbrushed materials in a variety of combinations on varied surfaces such as ceramic bathroom tiles, glass, and even a beer stein to see how they would bond with each surface. In some instances, researchers added in solar cells that converted power from a white laboratory light.

In at least one of the experiments, the batteries alone powered light-emitting diodes that spelled out "RICE" for six hours, with a steady 2.4 volts.

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The research team worked hard to create just the right mix of layers capable of bonding, which included a blend of single-wall carbon nanotubes; a cathode that contained lithium cobalt oxide; carbon and graphite powder; a polymer separator paint of resin and silicon dioxide dispersed in a solvent mixture; an anode that was a mixture of lithium titanium oxide; and a negative current collector that used commercially available copper paint diluted with ethanol.

"The hardest part was achieving mechanical stability," said Singh. "We found that the nanotube and cathode layers were sticking very well, but if the separator was not mechanically stable, they would peel off." Once researchers had tried a few combinations, she added, they were able to stabilize the elements as they were "painted" together.

What is most interesting is that the painted batteries were easily charged with just a small solar cell. While solar technology companies have taken a public beating in the media and the political arena in the past year--e.g., Solyndra--solar and energy storage researchers have quietly begun to chart a path that could truly change the world. This new research could be yet another game-changer.

Because the paintable batteries are flexible, cheap, and can be easily charged by just a small solar cell, Singh said she can already see the possibility of integrating paintable batteries with the concept of paintable solar cells (new research that was also announced to little fanfare earlier this year) to create an energy-generating and energy-storage combination that could be revolutionary.

"Spray-painting is already an industrial process, so it would be very easy to incorporate this into industry," Singh said. "We really do consider this a paradigm changer."

The Rice research team has filed for a patent on the technique, but it's also looking to further develop the process to make it easier to create painted batteries in the open air or even create batteries that can be snapped together like LEGOs and attached to anything.

But one thing is certain. While the occasional failures of companies like Solyndra make for easy targets of headline-hunting congressional investigators, researchers like Singh and Ajayan at Rice are quietly developing new technologies that could forever alter the way in which consumers get access to energy through cheap, ubiquitous, paintable batteries that can run their consumer electronics.