Aug 21, 2010

Rechargeable Auto Battery Update

Rechargeable batteries are enmeshed in our every day life for personal electronics. But they are becoming an ever important part of auto transportation.

The hybrid vehicles such as Honda Civic and Toyota Prius already rely heavily on rechargeable technology but the soon to arrive fleet of Electric Vehicles(EV) will rely almost totally on rechargeables since there will be no(or very little) oil and gas required to operate.

The Nickel Metal Hydride batteries that power the early models of hybrids are not offering as long a life as promised at the date of auto purchase 

Here are excerpts from an Economist article on the state of the rechargeable auto battery market.

 The rechargeable nickel-metal hydride cell has been one of the great success stories of battery development, at least technically, if not commercially. It is a direct descendant, with all the benefits and more, yet few of the drawbacks, of the nickel-cadmium (NiCad) battery used for decades for heavy-duty tasks like starting aircraft engines and powering forklift trucks.
As in a NiCad battery, the NiMH’s anode is made of nickel oxyhydroxide immersed in an electrolyte of potassium hydroxide. The cathode, however, is composed of a harmless hydrogen-absorbing alloy instead of toxic cadmium. Weight for weight, a NiMH cell can store two to three times more energy than its cadmium-based predecessor. This alone has made it a favourite among hybrid carmakers such as Honda and Toyota.

The best guess about what is happening is that it has something to do with the way the batteries are charged and discharged during use. Unlike pure electric cars, hybrids normally have a rather shallow charge-discharge cycle. A hybrid’s battery is replenished constantly by the engine as well as by the vehicle’s regenerative braking system. As a result, it is hardly ever fully drained. That ought to make it last longer than the battery of a plug-in electric vehicle.

If a cell does get fully drained, though, it can go into a state known as polarity reversal, in which the surrounding good cells drive the bad one in reverse. The drained cell then becomes permanently crippled and unable to contribute to the battery’s overall output. If that happens to several of its cells, a battery can no longer hold anything like its full charge.

So, what could trigger such a deep discharge in a hybrid’s battery? Small differences in the manufacturing tolerance of a battery’s cells may play a part. Also, charging a NiMH battery is a tricky business because the voltage has to be carefully reduced as the amount of energy being stored increases. A fault in the voltage-control mechanism may thus cause a battery to become overcharged, which, in turn, might precipitate a deeper discharge than normal. A third possibility is that the design of the battery’s service plug—a disconnection mechanism for splitting it into two isolated halves so that its terminals are no longer live when the vehicle is being serviced—might be prone to intermittent shorting.

Whatever the cause, any deterioration in a battery’s ability to hold a charge can affect not only its willingness to propel the vehicle, but also the rate at which it spontaneously leaks electricity—especially if its temperature rises as a result of polarity reversals. Nickel-metal hydride cells discharge faster in this way than other batteries do; and the higher their capacity, the more prone they are to such self-discharging. Accelerated self-discharge might explain the problem of fully charged batteries draining themselves while their owners are shopping.

Most of NiMH batteries used in hybrids like the Prius and the Civic are made by Panasonic and Sanyo (now part of the same organisation) under licence from a joint-venture between Chevron, an oil company based in California, and Energy Conversion Devices of Michigan, one of the battery’s inventors. Chevron acquired its share of the intellectual property in 2001 when it bought Texaco, which had previously bought the rights to NiMH technology from General Motors, after GM pulled the plug on its original electric-vehicle programme.

The tight supply of nickel-metal hydride batteries has much to do with licensing restrictions and the way the key patents have been enforced. Critics of Chevron—including Stanford Ovshinsky, co-inventor of the NiMH battery and founder of Energy Conversion Devices—believe the firm sat on the technology after acquiring it, instead of actively promoting it. To be fair, the company’s claim to need orders for upwards of 100,000 batteries annually for three successive years before starting a production run is not unreasonable, given the cost of the tools required to make the batteries. Even so, the effect was to force many would-be makers of electric-vehicles to abandon their efforts, or to adopt inferior solutions instead.

In the end, protracted law suits brought by several big electric-vehicle makers, including Mercedes-Benz, culminated in the NiMH technology being sold in 2009 to SB LiMotive, a battery-making venture established by Samsung of South Korea and Robert Bosch of Germany. The intellectual property's change of ownership may help increase the availability of NiMH batteries, but mainly for Korean and German carmakers rather than American and Japanese ones.

Meanwhile, the NiMH battery is facing its first serious challenge. The new generation of plug-in hybrids and pure electric vehicles like GM’s forthcoming Volt (Ampera in Europe) and Nissan’s Leaf need more powerful batteries than those used in previous generations of hybrid cars. As a result, carmakers have embraced the lithium-ion battery. While far trickier to handle, lithium-ion cells pack twice the punch of their nickel-metal hydride equivalents.
With the one crucial patent—for the lithium cobalt oxide cathode—having expired in 2002, manufacturers have none of the “patent encumbrance” constraints they faced with nickel-metal hydrides. Besides, the know-how for producing lithium-ion batteries is now widely dispersed, thanks to the pioneering work done by laptop and mobile-phone makers.

That said, your correspondent still thinks the lithium-ion battery’s cooling, toxicity and recycling problems, not to mention the price and scarcity of its materials, will prove a bigger constraint than patent encumbrance was for its predecessor. And while lithium-ion batteries do not self-discharge in the way their NiMH cousins do, they can lose 20% a year of their capacity as a result of deposits that form in the electrolyte. At higher temperatures, these losses can amount to 35% a year. The implication is that if you live in a warm climate, you could be changing your electric car’s lithium-ion battery every three or four years. Perhaps NiMH, for all its faults, will be around for a while yet.

from the Economist.com 8-20-10 The Difference Engine:Flat Battery

The ongoing conundrum of how to get  materials to power our world that are reliable but not too damaging to the environment from a development(ie mining of the elemental material) to disposal to everyday use.
But as caustic as the mining of the minerals to support these batteries may be is it not still better than all the baggage oil and gas brings.
Interesting to see Chevron is involved. The oil and gas giants keep their pinkies in alternative energy just in case it finally overwhelmes traditional oil and gas as the transport energy of choice

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