Toyota ran into similar troubles when its Prius hybrid car was introduced over a decade ago. Though the Priuss battery pack is considerably smaller than the Volts, fire-fighters and other first-responders had to learn how to disarm the vehicle following an accidentby removing fuses from under the bonnet and pulling a catch beneath the rear storage area to isolate the high-voltage system. Until they had done so, they were warned, they were on no account to take a metal cutter to an overturned Prius to extricate trapped occupants. Lurking beneath the floor was a big orange cable carrying a heavy current that would have fried anyone slicing through it.
The lithium-ion cells used in the Volts battery pack have many virtues. They are much lighter and operate at a higher voltage than other rechargeable cellsand can therefore store more energy for a given weight. In addition, they have no memory effect and can also hold their charge far longer than, say, the nickel-metal hydride cells used in the Prius. For good reason, all plug-in electric vehicles, including the Nissan Leaf and the forthcoming Ford Focus Electric plus Toyotas long-awaited plug-in Prius, have embraced lithium-ion chemistry.
But lithium is a highly reactive element. If overcharged, physically damaged or allowed to get too hot, lithium-ion cells can experience thermal runaway and even explodeas has happened on numerous occasions with the lithium-ion batteries in laptop computers and mobile phones. Also, if allowed to drain completely, they can short-circuit and make recharging dangerous. For these reasons, all lithium-ion rechargeable batteries contain circuitry that shuts them down when their voltage rises above or falls below a certain level.
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2016-02-26
2016-02-26
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2016-02-26