“Nano” will surely be the word of the year in science and “graphene” – I predict – will be the material of the year. No doubt the words will also be used to generate unjustified publicity in many cases. But such is the interest and the potential that the developments in nano-technology will accelerate and it will not be long before applications are in every-day use. One of the limiting factors is the availability of energy sources at the nano-scale but even that limitation may soon be overcome.
A research team at Rice University have managed to squeeze a whole lithium-ion energy storage device into a single nanowire, which could be used as a rechargeable power source for future generations of nanoelectronics. The work is reported in a paper published by the American Chemical Society’s Nano Letters
Building Energy Storage Device on a Single Nanowire by Sanketh R. Gowda, Arava Leela Mohana Reddy, Xiaobo Zhan, and Pulickel M. Ajayan, Nano Lett., DOI: 10.1021/nl2017042, July 14, 2011
Nano-wire battery
Abstract
Hybrid electrochemical energy storage devices combine the advantages of battery and supercapacitors, resulting in systems of high energy and power density. Using LiPF6electrolyte, the Ni–Sn/PANI electrochemical system, free of Li-based electrodes, works on a hybrid mechanism based on Li intercalation at the anode and PF6– doping at the cathode. Here, we also demonstrate a composite nanostructure electrochemical device with the anode (Ni–Sn) and cathode (polyaniline, PANI) nanowires packaged within conformal polymer core–shell separator. Parallel array of these nanowire devices shows reversible areal capacity of
3 μAh/cm2 at a current rate of 0.03 mA/cm2. The work shows the ultimate miniaturization possible for energy storage devices where all essential components can be engineered on a single nanowire.
From PC World:
A team of scientists has created a battery so small that it fits into a “nanowire,” a wire whose thickness is less than the wavelength of visible light. It’s the smallest battery ever made, and it could end up powering a whole generation of nanotechnology.
The potential of nanotechnology—the practice of building machines so small that they can’t even be seen—has been talked about for decades. In medicine, for example, the idea of creating tiny robots that could enter a person’s bloodstream and target intruders or diseased cells has been touted as one of the most promising applications of the field, but it’s remained purely theoretical.
One of the hurdles standing in the way of such wondrous nanodevices is their power supplies—making batteries at such a tiny scale is difficult. Now a team of engineers from Rice University appears to have solved that problem by creating a battery just 50 microns, or about the thickness of a human hair.
To create the battery (see the diagram), the researchers first coated a nanowire template with a thin layer of copper. They then filled the pores (which create the individual nanowires) halfway with a nickel/tin alloy to create the anodes. At this point, they put on a thin layer of polyethylene-oxide gel, which acts as both an electrolyte and an insulator from the other nanowires. Next they filled the remainder of the pore with a polyaniline material to create the cathodes. A layer of aluminium goes on top to complete the circuit.
Every nanowire is just 150 nanometers (nm) thin. To put that in perspective, the lowest wavelength of visible light is about 400 nm. However, the complete battery is about 50 microns tall, or about the width of human hair. The researchers ended up creating an array of nanowire batteries that was about 0.08 square inches in area, though it’s theoretically scalable to even larger sizes.
With a larger array that includes several layers stacked on top of each other, the tech could theoretically lead to batteries with massive energy density. And since the electrochemical materials don’t contain lithium, they’re easy to synthesize and manipulate at room temperature.
The nanowire batteries aren’t without their limitations, however. After being charged and discharged 20 times, they lose their ability to hold a full charge. The researchers are working on addressing this limitation, however, by playing with the polymer thickness and trying out different kinds of electrodes.
Although it’s in the early stages, the new battery technology could help usher in an era of practical nanomachines. With a real microscopic power source, the science-fiction scenario of tiny machines acting as doctors, builders, and explorers just took a step toward reality.
The team had reported last December on the creation of 3-D nano-batteries
Last December, Ajayan’s team encased vertical arrays of nickel-tin nanowires in PMMA, which is a polymer known as Plexiglas. The Plexiglas was an electrolyte and insulator in this case, and the nanowires were grown by electrodeposition in an anodized alumina template on top of a copper substrate. The template’s pores were stretched with a chemical etching technique, causing a gap between the alumina and the wires, and then the researchers drop-coated PMMA to enclose the wires with a smooth covering. The template was removed with a chemical wash, and a forest of tiny electrolyte-encased nanowires appeared. This particular battery had encased nickel-tin as the anode and a cathode had to be attached to the outside, but in the new battery packs, the cathode is packed into the nanowires.
The team created two versions of the battery pack. The first combines a nickel-tin anode, polyethylene oxide (PEO) electrolyte and polyaniline (PANI) cathode layers, which allows for the efficient movement of lithium ions through the anode to the electrolyte and the cathode. The ions are stored in bulk allowing the device to charge (and discharge) rapidly.
The second version squeezes the same characteristics into a single nanowire, with centimeter-scale arrays containing thousands of nanowire devices where each is approximately 150 nanometers wide.
The new process uses PEO as the electrolyte, which stores lithium ions and acts as a electrical insulator between the nanowires in an array. The widened alumina pores were drop-coated with PEO to coat the anodes, and leaves tubes at the top allowing PANI cathodes to be drop-coated as well. The circuit is finished off with an aluminum current collector placed at the top of the array.
The k2p blog 