Ed Schweppe (edschweppe) wrote,
Ed Schweppe

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Cellulose-based batteries?

I found this little item in the August 16 edition of The Economist magazine: It looks good on paper
ELECTRICITY-storage devices are getting more flexible, in a literal sense as well as in their design. This week saw the unveiling of the most robust but flexible battery ever reported. Pulickel Ajayan and his colleagues at Rensselaer Polytechnic Institute in New York made it by mixing carbon nanotubes (cylindrical, electrically conductive molecules made of carbon atoms) with cellulose, the stuff of paper. The result, which they reported in the Proceedings of the National Academy of Sciences, is an energy store that is cheap, flexible and paper-thin.

[ ... ]

The result is a material that works at temperatures from –80°C to 180°C, and can be rolled up, folded or cut like paper with no effect on its performance. It could be attached to folding solar panels of the sort used in space missions, and back on Earth it could provide portable power in deserts or at the poles.

The three-layer version, in particular, provides a unique hybrid power supply. It has the characteristics needed for applications that require both high-power pulses and steady, battery-like flow. Moreover, it provides them both while it is discharging and while it is being re-charged. Hybrid cars are one application for these characteristics. Many use dynamos to recover their energy of motion when they brake. The recovered energy is normally stored in a battery. But such a car needs a burst of energy to get going again. Dr Ajayan's device could provide this more effectively than a conventional battery.
A little more searching turned up this interesting fact about the new technology, as reported in ScienceNow:
Each gram of paper produces about 10 milliamps of current at 2 volts, and the researchers were able to use the batteries to power a fan and LED light. Stacking multiple sheets increases the power, the team reports online this week in the Proceedings of the National Academy of Sciences. Unlike other flexible batteries, the paper battery is completely integrated, says Linhardt.
For those counting at home, that's 20 milliwatts of power from one gram of paper battery. Arbitrarily assuming that the reported performance was at the 20-hour rate (generally the standard for lead-acid batteries), that would imply an energy density of 400 watt-hours per kilogram. So what? Well, according to this page from BatteryUniversity.com, that figure is ten times the energy density of standard lead-acid batteries, and better than twice the energy density of the best lithium-ion chemistries (see figure 4, about half-way down).

This is way cool stuff. (Assuming, of course, it can handle real-world conditions.)

The news articles I've seen talk mostly about the uses in applications such as off-grid power, implantable medical devices (cellulose being remarkably non-toxic), hybrid vehicles and the like. But there's another, potentially huge, market out there. Right now, one of the biggest hurdles that renewable electricity sources have to overcome is the fact that the best renewables (wind and solar) aren't really schedulable - if a cloud passes overhead or the wind dies down, your renewable generator doesn't generate. Cheap, non-toxic batteries made with this new cellulose technology take care of that little problem quite nicely. In fact, I can easily see roofing panels, made from cellulose batteries and thin-film solar cells, replacing asphalt shingles on the roofs of the world. (And there are a lot of roofs out there, the vast majority of which spend an awful lot of time in the sunshine.)

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