Wrapping paper that lights up to say 'happy birthday' is just one potential application of a battery that's basically made out of paper.
Scientists have been working for some time to develop light, ecofriendly, inexpensive batteries consisting entirely of nonmetal parts, with the most promising materials including conductive polymers or 'plastic electronics'.
One of these, polypyrrole (PPy), showed promise, but was often regarded as too inefficient for commercial batteries. But by coating PPy on a large surface area substrate and carefully tailoring the thickness of the PPy coating, both the charging capacity and the charging rates have been drastically improved.
The trick is to use an uninterrupted, nano-thin coating of PPy on individual cellulose fibers, which in turn can be molded into paper sheets of exceptionally high internal porosity.
The team used cellulose extracted from a certain species of green algae which has 100 times the surface area of cellulose found in paper. The surface area was key to allowing the new device to hold and discharge electricity very efficiently.
Both electrodes consist of identical pieces of the composite paper separated by an ordinary filter paper soaked with sodium chloride serving as the electrolyte.
The battery recharged faster than conventional rechargeable batteries, and could be suited to applications such as clothing and packaging, say the scientists. Another possibility is low-cost energy storage devices with electrodes measuring several square yards.
Details appear in ACS' Nano Letters.