Batteries that can be printed onto a surface with "nanotube ink" have been demonstrated by US researchers, who say the technique will fit well within the growing field of printed electronics, which still use conventional power sources.

The batteries were created by George Gruner and colleagues at the University of California in Los Angeles, US, and use the same zinc-carbon chemistry as ordinary non-rechargeable batteries.

Being able to print flexible batteries onto different surfaces should prove handy for powering disposable devices, such as long-range RFID tags or small displays, the researchers say.

The batteries are made from two layers containing carbon nanotubes and a third layer of zinc foil, and are less than a millimetre thick.

A great many carbon nanotubes can be packed into these layers. They form randomly aligned nanotube networks that conduct charge more efficiently than the metals normally used - connecting many points in the battery simultaneously, without hampering the electrochemical process that generates power.

Increased power

To make the battery, a layer of nanotubes is first deposited in the form of "nanotube ink" onto a surface. This layer acts as the charge collector, which removes current from the battery.

Next, a layer of nanotube ink mixed with manganese oxide powder and electrolytes, which carries charge within the cell, is applied on top. This layer acts as the cathode. Finally, a piece of zinc foil - the anode - is applied.

"The batteries are similar to conventional batteries," says Gruner, "with the electrically conducting nanoscale networks replacing conventional metals and electrodes."

He adds that the designs should make it possible to get more power than a conventional design would from the same materials, , "an important factor for portable electronics applications."
Industrial production

The researchers also made supercapacitors using the inking technique and plan to combine these with batteries for applications requiring more power.

Furthermore, since both printed batteries and supercapacitors can be made entirely at room temperature, it should be possible to mass-produce them using established printing methods, Gruner says.

Chemist George Chen at Nottingham University, UK, agrees that nanotubes could provide ways to improve battery performance. But he points out that Gruner's batteries were only tested at low power. "The discharge currents are, so far, smaller than needed for practical use."

However, Gruner says his research team is working to increase power output and to demonstrate suitability of the designs for industrial production.