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February 2010
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Paper Battery

Presently, battery takes up a huge amount of space and contributes to a large part of the device’s weight. There is strong recent interest in ultrathin, flexible, safe energy storage devices to meet the various design and power needs of modern gadgets. To build such fully flexible and robust electrochemical devices, multiple components with specific electrochemical and interfacial properties need to be integrated into single units. Fuel cells and solar power have both been floated as promising solutions to the battery weight/capacity problem, but new research suggests that carbon nanotubes may eventually provide the best hope of implementing the flexible batteries and supercapacitors needed to shrink our gadgets even more. Researchers say that flexible paper batteries could meet the energy demands of the next generation of gadgets. A paper battery is a flexible, ultra-thin energy storage and production device formed by combining carbon nanotubes with a conventional sheet of cellulose-based paper. A paper battery acts as both a high-energy battery and supercapacitor, combining two components that are separate in traditional electronics. This combination allows the battery to provide both long-term, steady power production and bursts of energy. Non-toxic, flexible paper batteries have the potential to power the next generation of electronics, medical devices and hybrid vehicles, allowing for radical new designs and medical technologies.

Making of Paper battery
The devices are formed by combining cellulose with an infusion of aligned carbon nanotubes that are each approximately one millionth of a centimeter thick. The carbon is what gives the batteries their black color. These tiny filaments act like the electrodes found in a traditional battery, conducting electricity when the paper comes into contact with an ionic liquid solution. Ionic liquids contain no water, which means that there is nothing to freeze or evaporate in extreme environmental conditions. As a result, paper batteries can function between -75 and 1500C. A capacitor introduced into an organism could be implanted fully dry and then be gradually exposed to bodily fluids over time to generate voltage. Flow of electrical power or electrons in a paper battery is governed by the steps as:

* Batteries produce electrons through a chemical reaction between electrolyte and metal in the traditional battery.
* Chemical reaction in the paper battery is between electrolyte and carbon nanotubes.
* Electrons collect on the negative terminal of the battery and flow along a connected wire to the positive terminal
* Electrons must flow from the negative to the positive terminal for the chemical reaction to continue.

Developments
Widespread commercial deployment of paper batteries will rely on the development of more inexpensive manufacturing techniques for carbon nanotubes. Early prototypes of the device are able to produce 2.5 volts of electricity from a sample the size of a postage stamp. One method of manufacture, developed by scientists at Rensselaer Polytechnic Institute and MIT, begins with growing the nanotubes on a silicon substrate and then impregnating the gaps in the matrix with cellulose. Once the matrix has dried, the material can be peeled off of the substrate, exposing one end of the carbon nanotubes to act as an electrode. When two sheets are combined, with the cellulose sides facing inwards, a supercapacitor is formed that can be activated by the addition of the ionic liquid. This liquid acts as an electrolyte and may include salt-laden solutions like human blood, sweat or urine. The high cellulose content (over 90%) and lack of toxic chemicals in paper batteries makes the device both biocompatible and environmentally friendly, especially when compared to the traditional lithium ion battery used in many present-day electronic devices and laptops.

Applications
As a result of the potentially transformative applications in electronics, aerospace, hybrid vehicles and medical science, however, numerous companies and organizations are pursuing the development of paper batteries. The paper-like quality of the battery combined with the structure of the nanotubes embedded within gives them their light weight and low cost, making them attractive for portable electronics, aircraft, automobiles, and toys (such as model aircraft), while their ability to use electrolytes in blood make them potentially useful for medical devices such as pacemakers. The medical uses are particularly attractive because they do not contain any toxic materials and can be biodegradable; a major drawback of chemical cells. In order to be commercially viable, they would like to be able to make them newspaper size; a size which, taken all together would be powerful enough to power a car. 

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