Spray Paint Battery Can be Painted on Virtually Any Surface

Spray Painted Li-Ion Cells Characterization

(a) (Left) Glazed ceramic tile with spray painted Li-ion cell (area 5×5 cm2, capacity ∼30 mAh) shown before packaging. (Right) Similar cell packaged with laminated PE-Al-PET sheets after electrolyte addition and heat sealing inside glove box. (b) Mass distribution of components in a typical painted battery. (c) Cross-sectional SEM micrograph of a spray painted full cell showing its multilayered structure, with interfaces between successive layers indicated by dashed lines for clarity (Scale bar is 100 µm). (d) Charge-discharge curves for 1st, 2nd, 20th and 30th cycles and (e) Specific capacity vs. cycle numbers for the spray painted full cell (LCO/MGE/LTO) cycled at a rate of C/8 between 2.7−1.5 V. (f) Capacities of 8 out of 9 cells fall within 10% of the targeted capacity of 30 mAh, suggesting good process control over a complex device even with manual spray painting. Credit: Ajayan Lab/Rice University; From: Scientific Reports

By using spray-painted layers, each representing the components in a traditional battery, researchers at Rice University have developed lithium-ion batteries with consistent capacities that can be painted on almost any surface.

Researchers at Rice University have developed a lithium-ion battery that can be painted on virtually any surface.

The rechargeable battery created in the lab of Rice materials scientist Pulickel Ajayan consists of spray-painted layers, each representing the components in a traditional battery. The research appears today in Nature’s online, open-access journal 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 and of chemistry. “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.”

Lead author Neelam Singh, a Rice graduate student, and her team spent painstaking hours formulating, mixing, and testing paints for each of the five layered components – two current collectors, a cathode, an anode, and a polymer separator in the middle.

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 2.4 volts.

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.

Paintable Battery

(a) Simplified view of a conventional Li-ion battery, a multilayer device assembled by tightly wound ‘jellyroll’ sandwich of anode-separator-cathode layers. (b) Direct fabrication of Li-ion battery on the surface of interest by sequentially spraying component paints stencil masks tailored to desired geometry and surface. Credit: Neelam Singh/Rice University; From Scientific Reports

Each layer is an optimized stew. The first, the positive current collector, is 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 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.

“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.” Once painted, the tiles and other items were infused with the electrolyte and then heat-sealed and charged.

Singh said 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 an energy-harvesting combination that would be hard to beat. As good as the hand-painted batteries are, she said, scaling up with modern methods will improve them by leaps and bounds. “Spray painting is already an industrial process, so it would be very easy to incorporate this into industry,” Singh said.

The Rice researchers have filed for a patent on the technique, which they will continue to refine. 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 said.

Reference: “Paintable Battery” by Neelam Singh, Charudatta Galande, Andrea Miranda, Akshay Mathkar, Wei Gao, Arava Leela Mohana Reddy, Alexandru Vlad and Pulickel M. Ajayan, 28 June 2012, Scientific Reports.
DOI: 10.1038/srep00481

Co-authors of the paper are graduate students Charudatta Galande and Akshay Mathkar, alumna Wei Gao, now a postdoctoral researcher at Los Alamos National Laboratory, and research scientist Arava Leela Mohana Reddy, all of Rice; Rice Quantum Institute intern Andrea Miranda; and Alexandru Vlad, a former research associate at Rice, now a postdoctoral researcher at the Université Catholique de Louvain, Belgium.

The Advanced Energy Consortium, the National Science Foundation Partnerships for International Research and Education, Army Research Laboratories and Nanoholdings Inc. supported the research.

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