Plain white office paper could be the basis for efficient batteries. Scientists have converted sheets of them into efficient electrical storage devices using ink loaded with carbon nanotubes. This new spin on an ancient invention is the latest in a line of research striving to incorporate paper into batteries to reduce their weight, one of battery technology's major shortcomings.

To trim weight, researchers have tried several approaches, including the use of thin films of materials laid down as inks. The appeal of paper for centuries—its porous microscopic structure, which makes it ideal for holding onto inks—now intrigues researchers for modern applications, not to mention that paper is also a flexible, lightweight, affordable, well-established technology that is used everywhere and could be made from renewable sources.

To devise the novel paper batteries, materials scientist Yi Cui of Stanford University and his colleagues coated plain copy paper with black ink made with single-walled carbon nanotubes, which are electrically conductive pipes only billionths of a meter wide. Positive and negative electrodes—cathodes and anodes—were then applied as slurries dried on the nanotube-impregnated paper. (The cathodes were made from lithium manganese oxide nanorods, and the anodes made either from nanopowders of lithium titanium oxide or nanowires with cores of carbon covered with shells of silicon.)

The batteries were then dipped in an electrolyte of lithium hexafluorophosphate solution to connect the electrodes and sealed in a pouch. In this setup the nanotubes collected current from each electrode. "It provides a nice example of the combination of high tech with low tech," says materials scientist John Rogers at the University of Illinois at Urbana–Champaign, who did not take part in this research.

This reduction could help make electric and hybrid vehicles more feasible and could lead to longer-lasting mobile phones, laptops and other portable electronics. "The fabrication of inexpensive, flexible and lightweight batteries could revolutionize portable electronics," remarks materials scientist Francesco Stellacci of the Massachusetts Institute of Technology, who did not participate in this study. At large scales, they could also inexpensively help solar and wind farms store what energy they generate, Cui adds.

The carbon nanotubes bonded very strongly to the paper, obviating the need for adhesives that decrease performance and significantly increase production costs, Cui and his colleagues note. The battery could also bend and curl without losing its ability to conduct a charge and "can be easily laminated into flexible computers to power the devices," he suggests. The team noted in their paper that its technique is easily scalable for mass production, and that the ink could even be painted on with brushes, if desired.

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