Flexible battery, no lithium required

April 28, 2014 by Mike Williams
Rice University postdoctoral researcher Yang Yang holds an energy storage unit with the best qualities of batteries and supercapacitors in a scalable, flexible package. Credit: Jeff Fitlow

(Phys.org) —A Rice University laboratory has flexible, portable and wearable electronics in its sights with the creation of a thin film for energy storage.

Rice chemist James Tour and his colleagues 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 the lithium found in commercial batteries today.

The new work by the Rice lab of chemist James Tour is detailed in the Journal of the American Chemical Society.

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

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.

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.

A porous nickel-fluoride film less than a micron thick, seen here in an electron microscope image, is an effective electrode in a new type of battery created at Rice University. The flexible film combines the best qualities of supercapacitors and batteries for potential use in flexible electronics. Credit: Tour Group

"This is not easy to do, because materials with such high capacity are usually brittle," he said. "And we've had really good, flexible carbon storage systems in the past, but carbon as a material has never hit the theoretical value that can be found in inorganic systems, and nickel fluoride in particular."

"Compared with a lithium-ion device, the structure is quite simple and safe," Yang said. "It behaves like a battery but the structure is that of a supercapacitor. If we use it as a supercapacitor, 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."

Nickel-fluoride electrodes around a solid electrolyte are an effective energy storage device that combines the best qualities of batteries and supercapacitors, according to Rice University researchers. The electrodes are plated onto a gold and polymer backing (which can be removed) and made porous through a chemical etching process. Credit: Tour Group/Rice University

To create the battery/, 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.

Flexible battery, no lithium required
Rice University researchers have created a new flexible energy storage technology that uses no lithium. From left, postdoctoral researcher Yang Yang, Professor James Tour and graduate student Gedeng Ruan. Credit: Jeff Fitlow

"The numbers are exceedingly high in the power that it can deliver, and it's a very simple method to make high-powered systems," Tour said, adding that the technique shows promise for the manufacture of other 3-D nanoporous materials. "We're already talking with companies interested in commercializing this."

Rice graduate student Changsheng Xiang and postdoctoral researcher Gunuk Wang are co-authors of the paper.

The Peter M. and Ruth L. Nicholas Postdoctoral Fellowship of the Smalley Institute for Nanoscale Science and Technology and the Air Force Office of Scientific Research's Multidisciplinary University Research Initiative supported the research.

Explore further: Hybrid ribbons a gift for powerful batteries: Vanadium oxide - graphene material works well for lithium-ion storage

More information: "Flexible Three-Dimensional Nanoporous Metal-Based Energy Devices." Yang Yang, et al. J. Am. Chem. Soc., Article ASAP. DOI: 10.1021/ja501247f

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1 / 5 (1) Apr 28, 2014
""The numbers are exceedingly high in the power that it can deliver, and it's a very simple method to make high-powered systems,"

and the numbers are...what?
5 / 5 (1) Apr 28, 2014
energy density of 384 Wh kg^–1, and power density of 112 kW kg^–1
5 / 5 (2) Apr 28, 2014
That would be 150% energy density of Li-ion batteries (and 300 times the power density!)
Those numbers are almost too good to be true.
not rated yet May 02, 2014
Exponential progress gets me squiggly
5 / 5 (1) May 02, 2014
All their densities are mass densities. Useful for things like... cars, say. But if you want to convert to volumetric... their thickness is about 170 micron. So I'll approximate the entire mass as PET, neglecting the mass of the thin electrodes (sorry, but meh), .0263 g/cm^2 . So let's say that the electrodes are a bit denser and round to .03 g/cm^2 . A phone battery's like...4 cm by 6 cm, I'd say, so 24 cm^2, so every layer of material is .072 grams.

Now their energy density's 384 Wh/kg as added above, and a phone battery is like... 12 watt hours or so, (mine is at least). So we need 384/12 = 32, so 1/32 of a kilogram of these cells, 31.25 grams. 31.25 grams/.072 grams per layer is 417 layers. 417 layers * 170 microns per layer (not counting interconnects or anything) is 7 cm.

A phone battery of this material would need to be 7 cm thick to fit in the same area footprint as normal batteries and maintain the same energy available.
5 / 5 (1) May 02, 2014
1: great, I really applaud moving away from Lithium based technology
2: the supercapacitor aspects are also hugely innovative, and could rapidly drive down charge times, very useful for vehicles where you want to recharge in approximately the time it takes someone to fill their gas tank.
3: The energy density per kilogram is great.. but the energy density per cc is not so great, meaning the technology, if adapted, would likely see more presence in vehicles than in phones.
not rated yet May 04, 2014
those are stats for the theoretical model.
They're talking about using multiple layers, removing the PET weight/volume discrepency.
depending on the durability of the device, we might start seeing early versions incorporated into the or bezel cases of smartphones, but that's missing the picture I think.

the real story here is that type of energy density and power density combined without rare earth metals.
the flexibility part is more or less meh to me at this point.
transformer sized barrels of these could be used to regulate intermittent power sources like tidal, solar, wind and anything else that produces more power some times than others.

hard to decide what's going to be the silver bullet- electronic hydrocarbon catalysts for liquid fuel or something more along the lines of this.
not rated yet May 04, 2014
The flexible part is interesting because one could start thinking about building the casing from the battery material (or the body of a car if the lifetime of the battery is equal to, or in excess of, the lieftime of the car).

The merging of functionality, design and energy storage is way overdue.

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