 Could paper be the future of power in electronic gadgetry? Just as plastics unleashed a revolution in the manufacture of everyday materials, a new power source composed of cellulose, carbon nanotubes and a dash of liquid salts could revolutionize the energy behind gadgets from iPhones to pacemakers in a few years from now.
Essentially, it is a paper battery, supercapacitor and battery-supercapacitor hybrid device that could be used in a variety of energy storage applications. These devices are lightweight and flexible and are primarily composed of cellulose paper—an environmentally friendly and biocompatible material.
Based on biopolymers, nanotubes and electronics—the power paper works by using cellulose to separate aligned carbon nanotubes functioning as electrodes. The nanotubes are grown and the cellulose is dissolved in an electrolyte—in a regular battery (sulfuric) acid may be used, but in this case a room-temperature ionic liquid (otherwise known as a liquid salt)—is poured around it. After drying, a thin sheet of "nanocomposite paper" is left that "can be rolled up, twisted or bent to any curvature.
In addition to all that flexibility, the paper battery can also be cut up or stacked and it works at a wide range of temperatures, from –100 degrees Fahrenheit to 350 degrees F (without bursting into flame). And, depending on how the paper is made, it can function as a battery, a supercapacitor (an unusually efficient energy storage device that can deliver a quick burst of power) or both. Separating carbon nanotubes with cellulose to yield black-colored paper gives a commercial-grade supercapacitor, whereas separating carbon nanotubes from a layer of laminated lithium delivers a long-lasting battery and two-colored paper: black on one side, gray on the other.
The nanotubes on which the cellulose is cast, contact the paper at the molecular level with an enormous surface area, allowing the device to efficiently store and release power.
The power paper could also absorb salty bodily fluids, such as sweat or blood, to function as a supercapacitor. The use of these electrolytes based on bodily fluids suggests the possibility of the device being useful as a dry body implant, creating interest in the medical / surgical circles over the use of disposable paper defibrillators.
Paper Battery
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Uses could be as varied as :
- Small devices such as hearing aids that could be more quickly recharged & also where the batteries wouldn't wear out for extended periods.
- Monitoring/ surveillance systems that could use vibrational or any light energy to recharge thus extending charge lifetimes.
- In automobiles you could regeneratively re-use the energy of motion and therefore improve the energy efficiency and fuel economy.
- Power assistance / back-ups for solar, wind, UPS systems
So far, the researchers have achieved power densities of 1.5 kilowatts per kilogram in the supercapacitor version and tested it over 100 cycles of discharge and recharge, well short of the million or so typical for current commercial capacitors. They have only made one-inch square versions of the paper, but the unique composite structure already reduces the complexity of creating such devices as well as battery-capacitor hybrids.
If the power sheets can be rolled off a printing press, as scientists hope, the future of energy storage may be in paper.
Nanotube filaments on the battery's electrodes
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