Nanotubes Power Paper-Thin Battery
Collaboration among three separate groups of students at Rensselaer Polytechnic Institute has come up with the idea of a paper-thin battery. Made mostly of cellulose -- the main fiber in paper -- embedded with carbon nanotubes and an electrolyte, the devices actually can be used as a battery, a supercapacitor or a combination of the two, depending on how it's assembled.
08/14/07 2:48 PM PT
Clunky old batteries may soon be a thing of the past thanks to a new energy-storage device that looks and feels like a scrap of paper.
Developed by a team of researchers at Rensselaer Polytechnic Institute (RPI), the nanoengineered battery is 90 percent cellulose, made up of the same plant cells used in nearly every type of paper. Infused in that paper, though, are aligned carbon nanotubes, which act as electrodes and allow the battery to conduct electricity.
The result is a lightweight, ultra thin, completely flexible storage device that can be rolled, twisted, folded or cut into any number of shapes with no loss of mechanical integrity or efficiency. The paper batteries can also be stacked, like a ream of printer paper, to boost the total power output.
Details are outlined in the paper, "Flexible Energy Storage Devices Based on Nanocomposite Paper," published Aug. 13 in the Proceedings of the National Academy of Sciences. The project was supported by the New York State Office of Science, Technology, and Academic Research (NYSTAR), as well as the National Science Foundation (NSF) through the Nanoscale Science and Engineering Center at RPI.
'A Pleasant Surprise'
The idea for the innovation arose from a collaboration among students from three different research groups at RPI, Robert Linhardt, a professor of biocatalysis and metabolic engineering at the university, told TechNewsWorld.
"We have some very smart and inventive students working in our labs," he explained. The students -- some from Linhardt's lab, others focused on carbon nanotube work and others from a group specializing in electronics and energy storage -- "saw a need where we professors didn't," Linhardt explained. "It's been a pleasant surprise for all of us."
Roughly 18 months later, the team actually has three separate devices that can be used separately or together: The battery, a piece of paper a few inches across that is black on one side and gray on the other; a supercapacitor that's black on both sides; and a hybrid device, which combines the two and is essentially both types of paper fused together, Linhardt said.
Blood, Sweat and Tears
Taken together, the devices can provide the long, steady power output of a conventional battery as well as a supercapacitor's quick burst of high energy needed for starting things like engines.
The researchers used ionic liquid, essentially a liquid salt, as the battery's electrolyte, but they also printed paper batteries without adding any electrolytes and demonstrated that naturally occurring electrolytes in human sweat, blood and urine can be used to activate them.
The devices are completely integrated, and can be printed like paper.
"We're not putting pieces together -- it's a single, integrated device," Linhardt said. "The components are molecularly attached to each other: the carbon nanotube print is embedded in the paper, and the electrolyte is soaked into the paper. The end result is a device that looks, feels and weighs the same as paper."
Because the device itself contains no water, there's also nothing to freeze or evaporate, allowing it to function in temperatures up to 300 degrees Fahrenheit and down to 100 below zero.
Potential applications span the spectrum, including not just lightweight handheld devices but also automobiles, aircraft and boats. Because the paper could be molded into different shapes, such as a car door, it could spur a new generation of automotive innovations, for example.
Thanks to paper's essential biocompatibility, the devices also have potential as power supplies for devices implanted in the body.
The RPI team expects that the supercapacitor will likely be the first commercial product to hit the market as a result of the innovation, possibly in just a few years, Linhardt said.
However, before that can happen, the team has three goals to focus on, he said. First, it must make the devices perform consistently so that the voltage and power are always the same. Second, "we want to optimize them to store as much power as they can," he said.
Worthy of Applause
Several years ago, researchers at the University of Massachusetts made headlines for their use of naturally occurring bacteria to generate electricity from the mud in Boston Harbor, but in general, such power innovations are uncommon.
"Battery achievements are few and far between," Roger Kay, president of Endpoint Technologies, told TechNewsWorld.
"We've seen some flexible lithium polymer batteries, but mostly the changes in battery technology lately have been incremental, with just slight improvements in capacity or total kilowatt-hours," he explained. "New developments are to be applauded."
Cost, Capacity Concerns
When it comes to mass production, however, expense may be an issue, Peter Kofinas, professor in the Fischell Department of Bioengineering at the University of Maryland, told TechNewsWorld. "Carbon nanotubes are very expensive, so from the commercial standpoint, this would be very expensive if you want to make a large sheet out of this material."
There could also be problems with cycling, or the number of times the same device can be charged and discharged without losing power, Kofinas added. "I am not sure its performance would match other things currently available in the market, due to significant capacity fade upon cycling, he said.
Nevertheless, "the paper battery is a neat idea," he said. "This is an easy-to-fabricate device, and the proposed flexible capacitor/battery has potential."