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Articles - Publication Date 12.19.1994
Bellcore
Red Bank, N.J.
Flexible rechargeable plastic battery
By Tim Stevens
Picture a battery. what do you see? Perhaps a small box such as a car battery, or a cylinder like the one powering a bunny across your TV screen, or a rectangular device for smoke alarms, or a button shape for a watch. Now imagine a lightweight sheet of flexible plastic about five feet wide and a tenth of an inch thick zooming out of a manufacturing line like newspapers or yard goods. Imagine you can cut this plastic sheet into any shape, fold it, twist it, poke holes in it, cram it into any space you wish, hook two wires to it -- and have it power anything from a laptop to an electric vehicle to devices we don't even know about yet.
Now consider that this plastic sheet contains no toxic, heavy, or reactive metals such as lead, cadmium, mercury, or lithium, as found in other battery technologies, nor does it leak or contain any dangerous liquids, such as sulfuric acid, as in your car battery.
Stop imagining and meet the new plastic rechargeable battery developed by Bellcore, Red Bank, N.J., the research arm of the Baby Bells.
Based on lithium-ion technology, though containing no metallic lithium, this thin-film plastic battery can deliver the same power at half the weight of nickel cadmium batteries (NiCAD, general purpose rechargeables) and at one third the weight of lead/acid batteries (car batteries).
It loses just 5% of its charge in a month's storage (3% per month thereafter) compared with 20% for NiCAD and 60% for nickel metal-hydride, a new nickel-based technology. Prototypes have been recharged 3,000 times (still recovering 70% of initial power) compared with typical cycle lives of about 1,000 recharges for NiCAD and 200 for lead/acid. Also, the Bellcore battery experiences no memory effect, or loss of the power not used if the battery is not discharged completely, a characteristic of NiCADs. To control the output of a Bellcore battery system just stack layers and connect them in series for more voltage, or increase the surface area via a bigger sheet to increase current. As impressive as these credentials are, the real breakthrough features of the battery are its thin-film, flexible form and its ability to be manufactured in existing plastic-film processing equipment.
"The form and flexibility of our battery will free designers from shape limitations -- give them degrees of freedom they never had before," says Vassillis Keramidas, executive director of Bellcore's energy storage group. "If I were to design a portable telephone, I would have to accommodate a rectangular space for the present batteries, which are bulky. Now, with the total flexibility that our battery provides, you can have a power source that fits the back of the telephone from top to bottom. Or if you want to roll it or fold it and stick it somewhere else, you can."
Today's cellular phones, for instance, are about 50% battery by weight. The Bellcore battery will allow new designs while also reducing the overall weight by one-quarter for the same performance or, at the same weight, doubling the time-in-use between recharges.
This lightweight flexible battery can be exploited in unique designs of today's portable electronic devices, such as laptops, pagers, games, personal digital assistants, and flat-panel displays. It could also drive development of completely new devices capitalizing on its form and manufacturability. "Our battery opens up a whole new world of electronic equipment," says battery-team member Frough Shokoohi. Some new applications already suggested include:
- Bar-code-type labels that broadcast information, that could be recharged and reprogrammed for their next use.
- Telephone credit cards that carry programmed units of "currency" for paying for calls. When all the units are spent, the system is recharged and reprogrammed with more exchange units.
- Card-like devices worn by employees to monitor exposure to dangerous gases or environments, including electronics and alarm systems.
- Batt
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