Flexible batteries pave way for bendable and wearable electronics

Researchers have developed a flexible material with nanoporous nickel-fluoride electrodes layered around a solid electrolyte to deliver battery-like supercapacitor performance that combines the best qualities of a high-energy battery and a high-powered supercapacitor without lithium.

Their 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 Rice postdoctoral researcher Yang Yang, co-lead author of the paper with graduate student Gedeng Ruan.

In tests, the students found their square-inch device held 76 percent of its capacity over 10,000 charge-discharge cycles and 1,000 bending cycles.

Chemist James 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.

To create the battery/supercapacitor, the team deposited a nickel layer on a backing. They etched it to create 5-nanometer pores within the 900-nanometer-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.

Testing found no degradation of the pore structure even after 10,000 charge/recharge cycles. The researchers also found no significant degradation to the electrode-electrolyte interface.

The study has been published in the Journal of the American Chemical Society.