Materials scientists at Rice University in Houston, Texas (US) have developed a rechargeable lithium-ion battery that can be painted on virtually any surface. The new fabrication technique would open the door to new design and integration possibilities for storage devices. Could Rice’s breakthrough be a leap towards hybrid devices that one day would marry paintable batteries with paintable photovoltaics?
“Paintable batteries have the capability of direct and seamless integration with objects. With the painting process, we have the flexibility to achieve batteries of any shape or size,” says Neelam Singh, a Rice graduate student and lead author of the research report “Paintable Battery” published in the journal Scientific Reports.
The Rice team’s work presents the concept of paintable batteries as well as its integration with photovoltaic technologies. “We foresee that components of solar cells can be painted on top of paintable batteries to achieve a hybrid device for solar energy capture and storage on any surface or object,” Singh says. She predicts that because this technique has “the potential to convert almost any outdoor surface to capture and store electricity, the total amount of solar energy harvested can be increased tremendously.”
The technology developed by Rice could one day enable standalone hybrid devices for capturing and storing solar energy. In fact, in their first lab experiment, Singh and her colleagues connected nine batteries spray-painted on bathroom tiles and attached a small, commercially available silicon solar cell that converted power from a white laboratory light. When fully charged, the paint-on batteries powered a set of light-emitting diodes that spelled out “RICE” for six hours; the batteries provided a steady 2.4 volts (see photo). Astoundingly, Singh reports that in the lab test the paintable batteries ran through more than 60 charge cycles “without any significant decay in the capacity.” The type of substrate did not affect the performance of the battery. They have used metals, glass, ceramics and flexible polymer sheets, as well as objects of different shapes, such as a beer stein. “At the lab scale the performance is satisfactory. And since spraying is already an industrial process, the paintable battery concept can easily be implemented in industries,” Singh says, adding that scaled up commercial fabrication would yield more uniform paint layers, which would greatly improve battery performance. “For applications where fast charging and discharging of the batteries is required, we can use nanomaterials for electrode paint formulations. The paint solvents can be replaced with more environment friendly solvents.”
The biggest challenge in developing this paintable battery was to achieve mechanical stability on various surfaces. While the nanotube and the cathode layers stuck well, the team realized that “the mechanical stability depended on the adhesion properties of the polymer separator and that ionic conductivity of the electrolyte was one of major factors that affect battery performance.” Eventually, “An adhesion promoter polymer was added in the polymer separator paint to achieve adhesion of batteries on practically any material,” Singh reveals.
Singh considers paintable batteries a paradigm changer: “This will ignite the research to improve the conversion efficiency of solar cells and formulating paints for solar cell components with environmentally friendly, low cost materials. Once we achieve these goals, we will be closer to the goal of bringing paintable batteries to homes.”
Photo: Rice University graduate student Charudatta Galande, Professor Pulickel Ajayan and graduate student Neelam Singh show the first test device for their paintable batteries, an array of standard ceramic tiles combined with a solar cell and an array of LEDs. (Credit: Jeff Fitlow/Rice University)