APS News

New Technologies, Materials Pave Way for Electric Vehicles

An efficient, commercially viable model for an electric battery-powered vehicle may soon be a reality, and physics is playing an important role in developing new materials and technologies to help achieve that end, according to speakers in a Monday morning session of the March Meeting.

"Every few years, for the last 40 years, we've heard that practical electric vehicles will be available 'in about five years,' and five years later, it's still years away," said Robert Stempel (GM Ovonic L.L.C.). "But we have a real chance to make it happen this time, thanks to technological advances in several disciplines. We are definitely headed towards commercially available electric vehicles."

Specifically, recent advances in electronics have made possible low-cost, durable computer controls to efficiently manage the use of electric power, and to handle high voltage and current without the losses associated with electro-mechanical devices. Most importantly, scientists have developed new materials that are making high-power, environmentally friendly, long-life batteries possible.

The move toward alternative power sources for vehicles is largely being fueled by environmental concerns and related legislation, particularly the Energy Act of 1992, which requires commercial fleets with 20 or more more vehicles to have a certain percentage of those operating on such alternate fuels as natural gas, electric, and ethanol/methanol. There are also state and other local measures in place. For instance, the state of California has mandated that by the year 1998, two percent of all new cars sold must be powered by "zero emission" engines.

The concept of an electric car is nothing new. In fact, according to Stempel, the first one was built in 1837, well ahead of the internal combustion engine. Nearly a century ago, when automobiles first appeared on the transportation scene, electrically powered vehicles had considerable advantages over gasoline: they were clean, quiet, easy to operate and dependable. By 1910, 30 percent of all vehicles were electric. However, as gasoline engines improved--for instance, the electric starter eliminated the need for hand cranking--they quickly became the preferred choice because of their greater flexibility and range.

Most earlier models for electric vehicles depended upon electric/mechanical devices for power distribution and control, resulting in inefficient use of energy and poor reliability. Batteries were heavy and their energy density was low. The highest possible energy density for lead-acid batteries is about 35 watt hours per kilogram, and 40 wh/kg for nickel cadmium batteries, according to Stanford Ovshinsky, president and CEO of Energy Conversion Devices (ECD). "The electric car has always been there, but there's been no battery to make it realistically practical," he said.

Such is no longer the case, thanks to the new Ovonic nickel-metal-hydride batteries, developed by ECD. Ovonic batteries are completely recyclable, have energy densities as high as 80 wh/kg, and can achieve driving ranges of between 140-200 miles on a single charge--all without using potentially dangerous materials like lead and cadmium. The design is the brainchild of Ovshinsky, who found that developments in the physics of disordered, multi-component, multi-phase materials could be applied to batteries, thus opening up new areas of use, such as portable telephones, laptop computers, and electric vehicles.

The Ovonic nickel-metal-hydride battery achieves energy storage through an electrochemical process that reversibly incorporates hydrogen into a solid hydride material, which exhibits high energy density, high power, and long cycle life. A broad range of multi-element metal-hydride materials that use structural and compositional disorder on several scales of length were engineered for use as the negative hydride electrode.

"When you have several elements, you get not only compositional disorder, but this in turn generates high density states," said Ovshinsky. "We get a tremendous amount of these so-called 'active sites' with a spectrum of bonding energies for the hydrogen by virtue of the various elements that are used. This enables us to thermodynamically control energy storage and release-- within the voltage offered by both electrodes."

General Motors experimented with a solar-powered car in 1987, called the Sunraycer, which was successful enough to convince Stempel that an electric vehicle was not only possible, but also commercially viable. Subsequent development efforts yielded GM's first Impact vehicle, powered with lead-acid batteries, which provided about a 50-mile range in city driving and up to 90 miles on the highway. Improvements continue to be made as new technologies are incorporated into the design. An Impact using nickel-metal-hydride batteries achieved over 200 miles on a single charge at highway speeds, while maintaining an acceleration rate of zero to 60 in eight seconds.

GM has signed an agreement to jointly manufacture Ovonic nickel-metal-hydride batteries for use by the electric vehicle industry, and initial production is in progress. Still, "electric vehicles are expensive, even using the lead-acid batteries, and the proposed long-range batteries are even more costly," said Stempel. "This is one reason GM decided to go ahead with the joint manufacturing venture: without volume capability and a continuous processing approach, the nickel-metal-hydride battery would always be costly."

Over the next five years, Stempel projects that there will be an increasing mix of electric and hydrogen fuel cell powered vechiles, as well as continuing advances in materials technology, such as lighter weight, higher strength materials for structures, and cheaper, improved alloys for higher power densities in batteries. "We are now on the steep part of the technology learning curve," he said. "We need to encourage continued development using flexible production techniques that permit rapid change, in order to incorporate improvements as they are developed and confirmed."

However, while the emerging electric vehicle industry is dependent on the development of new technology, Stempel is careful to emphasize that technological applications must be done in a "user-friendly" manner, so that potential customers will prefer an electric vehicle to meet their transportation needs. "This time we are not introducing a vehicle to replace the horse," he said. "We will be competing with very good gasoline-powered cars, and potential customers will expect the new vehicle to provide improvements without losing today's attractive features."

According to Hank Courtright of the Electric Power Research Institute, the successful deployment of electric vehicles will require new infrastructures for convenient and safe charging. The technical feasibility of a number of charging configurations has been proven and commercial availability of charging systems for residential installation--as well as public services at retail locations and parking lots--is fast becoming a reality. But Courtright warned that the need for rapid charging and management of power quality may call for new utility load requirements and significant re-engineering of the present distribution system.

Apart from the practical benefits of producing electric vehicles, Ovshinsky feels that building new industries that employ workers with science and technology backgrounds is an equally important objective. "Science shouldn't be considered a 'value-free' discipline," he said. "We should be serving society and applying science and technology to help solve societal problems. The development of the Ovonic nickel-metal-hydride battery is a very good model of how that can be done."


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