Researchers develop paintable batteries

The rechargeable battery consists of five spray-painted layers – two current collectors, a cathode, an anode and a polymer separator in the middle – which each represent the components in a traditional battery. "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," said materials scientist Pulickel Ajayan. To test the technique, the materials were airbrushed 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 2.4V. The researchers reported that the hand-painted batteries were remarkably consistent in their capacities, within plus or minus 10% of the target. They were also put through 60 charge-discharge cycles with only a very small drop in capacity. "The hardest part was achieving mechanical stability, and the separator played a critical role," said graduate student Neelam Singh. "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 [a transparent thermoplastic] gave the right adhesion to the separator." Once painted, the tiles and other items were infused with the electrolyte and then heat-sealed and charged. According to Singh, the batteries were easily charged with a small solar cell. She foresees the possibility of integrating paintable batteries with recently reported paintable solar cells to create a novel energy harvesting combination. "Scaling up with modern methods will also improve them leaps and bounds," Singh noted. "Spray painting is already an industrial process, so it would be very easy to incorporate this into industry." The Rice researchers have already filed for a patent on the technique, which they are continually trying to define. Singh said they are actively looking for electrolytes that would make it easier to create painted batteries in the open air, and they also envision their batteries as snap-together tiles that can be configured in any number of ways. "We really do consider this a paradigm changer," she concluded.