Cutting edge spray-on rechargeable battery design

US-GRAFFITI-SPRAY-PAINT A cutting-edge battery that can be spray-painted on just about any surface was unveiled Thursday by a research team that tested it on everything from bathroom tiles to a beer mug.
The design could revolutionise the design of lithium-ion batteries that power our laptops, cellphones and electric cars -- leading to slimmer, lighter devices with built-in power supplies.
Using liquid versions of the same components found in conventional lithium-ion batteries, the team airbrushed their invention, in several layers, on to a glass slide, a stainless steel sheet, glazed ceramic tiles, and the curved surface of a mug.
"Basically, using this approach, we can convert any object or surface to a battery," said lead author Neelam Singh, an engineering student at Rice University in Texas.
Lithium-ion (or Li-ion) batteries work by transferring a charge between a negative and positive electrode.
Compared to other rechargeable batteries, they are light, have a high power output and storage capacity, and are safer.
For the prototype, the team created liquid, paintable versions of the five layered components -- two electrodes, a cathode, an anode and a polymer separator.
"We first converted all the components of the battery into paints. We could then use these paints to literally paint batteries on any surface and using nothing but just a spraygun," said Singh.
The mug was used to show the paint's versatile application to objects of different shapes.
In one experiment, the team sprayed batteries on to nine bathroom tiles which they connected to each other.
One of the tiles had a solar cell attached to it, which was charged using a white laboratory light.
Once charged and connected, the tiles "delivered enough energy to power 40 red LEDs (light-emitting diodes) for more than six hours," said the team's report in the journal Nature Scientific Reports -- a steady 2.4 volts.
The researchers described the breakthrough as a "paradigm change in battery design".
Unlike existing batteries, the paintable version does not require an extra compartment for storage, and could thus be more easily integrated into existing designs for battery-powered devices.
It also opens up exciting possibilities for solar power generation and storage.
"The ceramic tiles we converted into batteries could be used to build the entire exterior walls of a house," said Singh.
"A wall made of these batteries could then be covered with solar cells and this combination of solar cells and batteries could be used to capture and store the solar energy into useful electricity."
The painted batteries were put through 60 charge-discharge cycles, which revealed "only a very small drop" in capacity, said Singh.
The researchers have filed for a patent on the technique, which they continue to refine.
Paintable Li-ion batteries use toxic, flammable and potentially corrosive liquid electrolytes, and must be applied in an oxygen- and moisture-free environment, the researchers wrote.
"What would be exciting is the development of lithium-ion batteries that are not sensitive to air or moisture," co-author Charudatta Galande said.
"That would greatly reduce fabrication and packaging costs. With that you could perhaps envision a do-it-yourself spray kit that you could perhaps buy from home depots and paint a battery on any surface that you like at home."