New thin-film batteries to help usher in bendable, wearable electronics

Next-generation flexible, portable and wearable electronics may be closer to reality, thanks to a thin-film for energy storage developed by scientists.

James Tour and his colleagues at Rice University have developed a flexible material with nanoporous nickel-fluoride electrodes layered around a solid electrolyte to deliver battery-like super-capacitor performance.

The material combines the best qualities of a high-energy battery and a high-powered super-capacitor without the lithium

found in commercial batteries today, researchers said.

The electrochemical capacitor is about a hundredth of an inch thick but can be scaled up for devices either by increasing the size or adding layers, said Yang Yang, co-lead author of the research paper with graduate student Gedeng Ruan.

Researchers expect that standard manufacturing techniques may allow the battery to be even thinner.

In tests, they found their square-inch device held 76 percent of its capacity over 10,000 charge-discharge cycles and

1,000 bending cycles.

Tour said the team set out to find a material that has the flexible qualities of graphene, carbon nanotubes and conducting polymers while possessing much higher electrical storage capacity typically found in inorganic metal compounds.

Inorganic compounds have, until recently, lacked flexibility, he said.

"Compared with a lithium-ion device, the structure is quite simple and safe," he said.

"It behaves like a battery but the structure is that of a super-capacitor. If we use it as a super-capacitor, we can

charge quickly at a high current rate and discharge it in a very short time. But for other applications, we find we can set it up to charge more slowly and to discharge slowly like a battery," said Tour.

To create the battery/super-capacitor, the team deposited a nickel layer on a backing. They etched it to create 5-nanometre pores within the 900-nanometre-thick nickel fluoride layer, giving it high surface area for storage.

Once they removed the backing, they sandwiched the electrodes around an electrolyte of potassium hydroxide in polyvinyl alcohol.

The finding is detailed in the Journal of the American Chemical Society.