Researchers Create Smallest Battery Ever Made

Aug 2, 2011

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 diagrom below), 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.