Rechargeable paper sheets could help rewrite the book on electricity storage

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Lightweight, extremely thin, and foldable, sheets of "power paper" have been created by scientists that can store significant amounts of electric charge and may one day provide ultra-thin electricity storage for modern devices(Credit: Linkoping University)

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Using millions of tiny fibers of nanocellulose sheathed with a conductive polymer coating, scientists have created sheets of paper that can store significant amounts of electric charge. Dubbed "power paper," the material is able to be recharged many hundreds of time, and in mere seconds. It is also lightweight, requires no toxic chemicals or heavy metals to create, and may offer a renewable and prolific way to provide energy to all manner of devices.

According to one of the groups of researchers working on the new material in the Laboratory of Organic Electronics at Linköping University, power paper has the characteristics of ordinary paper with a slight plastic sheen. To demonstrate its flexibility and strength, the researchers claim they were even able to use one piece to fold an origami swan.

Just one sheet of the new electric paper, some 15 cm (6 in) wide and mere tenths of a millimeter thick, is able store as much as electric charge as a 1 Farad capacitor; an amount similar to currently available supercapacitors. According to the researchers, the new paper also holds four world records for any supercapacitor – the highest charge and capacitance in organic electronics, of 1 Coulomb and 2 Farad, the highest measured current in an organic conductor of 1 Ampere, along with the highest capacity to simultaneously conduct ions and electrons, and the highest transconductance in a transistor.

"Thin films that function as capacitors have existed for some time," said Xavier Crispin, professor of organic electronics. "What we have done is to produce the material in three dimensions. We can produce thick sheets."

The primary construction material used is nanocellulose, which is composed of cellulose that has been broken down into fibers around 20 nm in diameter. These nanocellulose

fibers are then soaked in water, and an electrically charged polymer, PEDOT:PSS (the same ingredient recently used in the production of weavable LED fibers and the creation of semi-transparent solar cells) in solution is added. The ensuing process then sees a thin patina of polymer form around the fibers.

"The covered fibers are in tangles, where the liquid in the spaces between them functions as an electrolyte," said Linköping University doctoral student Jesper Edberg.

With an exceptional capacity for energy storage, the researchers believe that continued development will eventually produce even higher capacity units. And with the new power paper being prepared like ordinary paper using regular cellulose pulp, which is dehydrated in the same way, the most significant challenge is to produce an industrial-scale process to accommodate this.

"Together with KTH, Acreo and Innventia we just received SEK 34 million (US$4 million) from the Swedish Foundation for Strategic Research to continue our efforts to develop a rational production method, a paper machine for power paper," says Professor Berggren.

Financed by the Knut and Alice Wallenberg Foundation since 2012, the power paper project also included researchers from the KTH Royal Institute of Technology, Innventia, the Technical University of Denmark and the University of Kentucky.

The results of this research were recently published in the journal Advanced Science.

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