Portland, Ore. -- Rensselaer Polytechnic Institute researchers said they have developed a paper-thin battery by immersing a carpet of vertical nanotubes in an ionic liquid electrolyte. The result is a cellulose paper that stores electrical energy.
The RPI team produced a supercapacitor by placing a second nanotube electrode on the other side of the paper. They then added a lithium electrode atop the paper, creating what they claim is a paper-thin rechargeable battery.
"The carbon nanotubes are embedded in the paper, and the electrolyte is soaked into the paper, so it really looks, feels and weighs about the same as paper," said RPI professor Robert Linhardt.
The supercapacitor and rechargeable battery are the results of a year and half of collaborative research among three RPI labs. One lab was making carbon nanotube-based structures, which were adapted to serve as battery electrodes. Growing the nanotubes vertically on a sheet, researchers poured liquid cellulose between the "forest of nanotubes" to form the battery. Another lab added a lithium-based top electrode to create either a rechargeable battery or a supercapacitor by adding a second nanotube electrode. Ionic liquids first dissolved the cellulose, turning it into a gel. The fluids also served as the battery electrolyte, carrying ions from one one side of the paper battery to the other.
Each sheet of battery paper generated about 2.4 volts with a power density of about 0.6 milliamps/cm2. For higher voltages, paper can be stacked. For more current, the sheets can be expanded to larger areas. The battery paper can operate in temperatures from –100°F up to 300°F and deliver quick surges of current, the RPI researchers said. It can also be rolled, twisted or cut into various shapes.
The researchers said they have recharged the paper batteries 100 times, with no deterioration in performance. Long-term testing will determine the maximum number of rechargings and optimize the design for higher power densities.
Since the paper is biocompatible, the researchers will also experiment with powering medical implants with paper batteries that could use blood and sweat as liquid electrolytes. They also want to perfect methods for printing batteries and supercapacitors using traditional roll-to-roll printing presses.