'Paint-on' batteries demonstrated
Researchers have shown off a means to spray-paint batteries onto any surface.
Their batteries, outlined in Scientific Reports, are made up of five separate layers, each with its own recipe - together measuring just 0.5mm thick.
To demonstrate the technique, the team painted batteries onto steel, glass, ceramic tile and even a beer stein.
The approach will be of particular interest in industrial applications, as it is compatible with existing spray-painting technology.
The most common batteries are made up of negative and positive halves (the anode and the cathode), a material to separate them, and "current collector" layers at top and bottom to gather up the electric charges moving through.
Many batteries are made in a kind of "Swiss roll" geometry, in which the layers are rolled up into a cylindrical or round-edged rectangular shape.
But as more consumer technology is developed with challenging shapes and sizes, or "form factors", the need for batteries of non-standard shapes is rising.
Flexible paper batteries have been demonstrated, and there is clear interest in "structural batteries" built for example into the surfaces of electric vehicles.
The new work, from Rice University in Texas, US, opens up completely new avenues for putting batteries on nearly any surface in a simple and robust way.
Pulickel Ajayan and his colleagues chemically optimised the recipe for each of their five layers, using blends of chemicals common in lithium-ion batteries as well as novel materials including carbon nanotubes - tiny "straws" of carbon with incredible electronic properties.
But for the process to result in a working battery, all five layers must stick together and work in synchrony, and the tricky step was finding a separator material that kept the whole stack in one piece.
When the team hit on using a chemical called poly-methylmethacrylate, they had a structure that would stick even to curved surfaces.
"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 Prof Ajayan.
"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."