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.
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The Cladophora cellulose-PPy conductive paper composite (a) SEM micrograph taken with a magnification factor of 10 000, (b) TEM image of the cellulose composite fiber, (c) schematic image, and (d) photograph of the composite paper battery cell before and after sealing it into an polymer coated aluminum pouch. Credit: American Chemical Society
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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.
"Ultrafast
All-Polymer Paper-Based Batteries"
SOURCE: American Chemical
Society
