Regular batteries contain a positive and negative electrode, both paired with a metal current collector, and a polymer separator sandwiched in the middle. These five layers are normally manufactured in sheets and rolled up into a cylinder, making it hard to create extremely thin batteries.
The Rice researchers have used a combination of existing metallic paints and custom materials to create sprayable versions of each layer, allowing them to make batteries just a fraction of a millimetre thick by airbrushing the layers onto a surface, one at a time.
'If the components of a battery, including electrodes, separator, electrolyte and the current collectors can be designed as paints and applied sequentially to build a complete battery on an arbitrary surface, it would have a significant impact on the design, implementation and integration of energy storage devices,' say the Rice researchers in a paper in Scientific Reports.
The researchers have fabricated rechargeable Li-ion batteries solely by multi-step spray painting of its components on metals, glass, ceramics and polymers.
The Rice researchers used five spray painted layers to make their batteries. A sticking point was finding the right material for the separator but polu-methylmethacrylate solved that one.
Single walled carbon nanotubes were also used. 'We found that high concentrations of SWNTs can be readily dispersed without the use of surfactants or polymeric binders,' said the Rice team.
The team also demo-ed a battery spray painted on a PV panel to provide an integrated energy capture and storage device.
The Rice team applied their batteries to a variety of ordinary building materials and even a ceramic drinks mug to test their potential. Nine bathroom tile batteries charged by a solar cell were able to power 40 LEDs arranged to spell out "RICE" for six hours. They don't yet match regular batteries - a paintable battery would have to be about 1.5 square feet to match a standard mobile phone battery - but that is set to improve.
The paints, as currently constituted, must be applied in a moisture-free and oxygen-free environment onto surfaces heated to 120 °C. The team are working on developing new battery materials which would not be degraded by air or moisture, which are non-toxic and safe to handle, and which can be used at home by non-experts while being environmentally friendly during use and disposal.