Imagine a gift wrapped in paper you really do treasure and want to carefully
fold and save. That's because the wrapping paper lights up with words like "Happy
Birthday" or "Happy Holidays," thanks to a built in battery - an amazing battery
made out of paper. That's one potential application of a new battery made of
cellulose, the stuff of paper, being described in the October 14 issue of ACS'
Nano Letters, a monthly journal.
 | | Batteries made of paper may power electronics in the future, researchers say. Shown are images from an experimental paper-based battery. Credit: The American Chemical Society |
Albert Mihranyan and colleagues note in the report that scientists are trying
to develop light, ecofriendly, inexpensive batteries consisting entirely of
nonmetal parts. The most promising materials include so-called conductive polymers
or "plastic electronics." One conductive polymer, polypyrrole (PPy),
shows promise, but was often regarded as too inefficient for commercial batteries.
The scientists realized, however, that 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 (discharging) rates can be drastically improved.
The secret behind the performance of this battery is the presence of the homogeneous,
uninterrupted, nano-thin coating - about 1/50,000th the thickness of a
human hair - of PPy on individual cellulose fibers which in turn can be
molded into paper sheets of exceptionally high internal porosity. It was special
cellulose, extracted from a certain species of green algae, with 100 times the
surface area of cellulose found in paper. That surface area was key to allowing
the new device to hold and discharge electricity very efficiently.
The innovative design of the battery cell was surprisingly simple yet very
elegant since both of the electrodes consist of identical pieces of the composite
paper separated by an ordinary filter paper soaked with sodium chloride serving
as the electrolyte. The potential difference is solely due to differences between
the oxidized and reduced forms of the functional PPy layer. The battery recharged
faster than conventional rechargeable batteries and appears well-suited for
applications involving flexible electronics, such as clothing and packaging,
the scientists say. Alternatively, low-cost very large energy storage devices
having electrodes of several square yards in size could potentially be made
in the future.
Posted September 23rd, 2009
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