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September 16, 2009

Smart Paper Battery Looks Hopeful for Green Market

By Kelly McGuire, TMCnet Editor

Sweden’s Uppsala University recently announced that researchers within the university have crafted a battery using two common and inexpensive substances: cellulose and salt. 

The lightweight and rechargeable battery uses thin pieces of paper – pressed mats of tangled cellulose fibers – for electrodes, while a salt solution acts as the electrolyte.

Maria Stromme, lead researcher at the university, said that the new battery should be inexpensive, easy to manufacture and environmentally friendly, and suggests that it could possibly be used to power cheap medical diagnostics devices or sensors on packaging materials.

And, since you don’t need advanced equipment to make these specific batteries, they could be constructed and supplied in various developing countries.

This simple, non-polluting battery that could possibly be used in compact devices is constructed with a type of rechargeable thin-film design that uses solid electrolytes instead of liquid or gel.

Sara Bradford, an energy and power consultant for Frost & Sullivan (News - Alert), said that these salt-and-paper batteries could be an ideal replacement for lithium batteries used in low-power portable devices such as wireless sensor and smart cards.

"For these applications, the thinner and smaller the battery, the better," Bradford said. 

These batteries have additional attractive features. 

Raghu Das, chief executive officer of IDTechEX, a research company, said that they have a long shelf life, retaining their charge after being stored for many years and can be charged and discharged tens of thousands of times.

With this battery makeup, wireless sensors can last for decades with an appropriate energy harvester attached, Das said.

While in theory, it’s a great idea, only a handful of startups have generated enough venture backing to bring their batteries to market. 

It seems as though the new paper battery still has some catching up to do.

While lithium batteries can deliver four volts and have energy densities of 200 to 300 milliwatt-hours per gram, a single paper battery cell delivers one volt and can store up to 25 milliwatt-hours of energy per gram. 

Despite the lower energy charge, Stromme said her team has tested the battery for 1,000 recharging cycles at a lower current. 

Researchers are working on optimizing the battery with hopes to eventually stack multiple cells together and connect them to increase the voltage.
One upside of the paper battery? It’s recharge ability.

The cellulose that Stromme and her colleagues use comes from a type of polluting algae found in seas and lakes. Although the algae's cell walls contain cellulose, it has a very different nanostructure, which gives it 100 times the surface area. 

The paper is then coated with this cellulose with a conducting polymer and then a salt-solution-soaked filter paper is sandwiched between the paper electrodes.

Despite the little kinks that still need to be ironed out, Stromme said she is confident that the environmentally friendly design will find niche applications and could be produced commercially within three years.

Kelly McGuire is a TMCnet Editor. To read more of her articles, please visit her columnist page.

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