PROBLEM: Can new batteries relieve anxiety over electric vehicles?
The public anxiety that accompanied last summer’s price spike of gasoline above $4 a gallon motivated many consumers to consider alternatives to gasoline-powered vehicles. As demand for gas-electric hybrids exceeded supply, both domestic and foreign auto manufacturers began accelerating plans for the first generation of all-electric vehicles.
While electric transportation alternatives are increasingly in fashion, the discussion will remain largely in the abstract until large numbers of vehicles are actually on the road. In the meantime, two fundamental technology challenges—the cost of electric vehicles and their relatively limited range—stand in the way of significant market penetration.
The batteries required for energy storage currently add thousands of dollars to the price of a hybrid or all-electric car. Even if cost is not a factor, many potential buyers are deterred by what the industry calls “range anxiety.” Even the best battery systems on all-electric vehicles must to be recharged after about 100 miles of use. Like drivers a century earlier who worried about running out of gas, car companies must overcome similar anxieties of today’s commuters and housewives who fear being stranded with a “dead” battery.
Developing technological solutions to these anxieties has become one of the key challenges for materials science researchers like ORNL’s Energy Materials Program manager, Craig Blue. “Traditionally, ORNL’s largest impacts have been in basic research,” Blue says. “Now we’re translating that capability into more applied areas. These areas include lightweight materials, like low-cost carbon fiber, and improvements in battery technology that will reduce cost and simultaneously improve range and reliability.”
“A successful transition to electric vehicles will require battery technology based on higher performing materials, more cost-effective manufacturing methods, and better systems integration that will reduce cost and provide more usable energy with no compromise of safety,” says Ray Boeman, ORNL’s Transportation Program Director.
“If we can reduce the weight of a passenger vehicle by 40 percent through the use of lightweight materials such as carbon fiber composites,” says Boeman, “we will translate that reduction into a 25 percent increase in fuel economy.” Due to the added weight of batteries, the need for lightweight vehicles is critical,” Boeman adds.
Carbon fiber appears to be the material with the greatest potential to reduce vehicle weight at a reasonable cost. However, carbon fiber is currently too expensive to be competitive with other materials in the mass market. “To reduce the cost, we are developing new ways of making carbon fiber, starting with new materials and new processes,” says composites researcher Cliff Eberle.
Today, most carbon fibers are made from petrochemicals using processes that have changed little in decades. Because these chemicals are derived from oil, their price is volatile and has fluctuated by a factor of three over the last year. “We are investigating other materials with costs that are lower and less volatile,” Eberle says.
One of these alternative materials is lignin, one of the most abundant polymers on earth. Lignin is also a low-cost byproduct of several industrial processes, like paper-making and the production of biofuels. Most importantly, lignin is a renewable product with no direct link to the price of oil.
Eberle and his colleagues at ORNL are working on a low-cost process to turn lignin into carbon fiber. “Traditionally carbon fiber is made using a fairly expensive, time- and labor-intensive heat treatment process,” Eberle says. “We are experimenting with microwave-assisted plasma to create the carbon fiber faster while using less energy.” Eberle believes his group will be able to process the carbon fiber in about a third of the time using half the energy of conventional methods. If successful, the new process would increase the throughput and reduce the cost.
Most of the expected weight-reduction benefits of low-cost carbon fiber would initially result from using carbon fiber for components such as body panels, fenders, doors, and hoods. In the longer term, Eberle also expects eventually to see carbon fiber components used in structural applications in the chassis and as driveshafts. Together, these new materials would lower the weight of the vehicle significantly.
In addition to increasing vehicle efficiency by reducing weight, ORNL’s pursuit of new battery technologies and improved manufacturing processes holds out the promise of lower cost and greater range for electric vehicles. "I think the Department of Energy is looking to ORNL for insight as to where we should go next with lithium ion batteries, as well as with the next generation of electric vehicle batteries," says Blue. "Industry wants to increase the distance battery power can go, so we are working to improve the range and reliability of the current generation of batteries, as well as to reduce production costs. We are exploring ways of streamlining the manufacturing process to make batteries more affordable so they are attractive to a broader spectrum of the public."
ORNL materials researcher Claus Daniel says that, in the past, battery research was primarily concerned with electro-chemistry. "Eventually, research determined that lithium-ion chemistries were the best for transportation applications because of their very favorable charge to weight ratio. Now our primary focus is taking this technology and addressing the fundamental issues of cost, reliability, and range."
Daniel believes these issues line up well with ORNL's historic strengths. "ORNL has a strong background in materials research, materials characterization, and process development." These capabilities, combined with the analytical capabilities of the Spallation Neutron Source and the laboratory's Center for Computational Sciences, provide ORNL an unprecedented ability to study the processes that cause batteries to degrade and to simulate structural and material alternatives that could result in longer battery life and greater reliability.
Daniel and his group are taking advantage of these unique capabilities at ORNL in collaborations with a number of academic and industrial research teams. The group is working with the University of Michigan to develop battery components that improve the performance and durability of lithium-ion batteries. They are also collaborating with battery manufacturers to incorporate into their products new types of electrodes and separator materials to boost reliability and reduce costs. This effort includes developing new manufacturing processes that can be used to scale laboratory prototype efforts up to commercial level.
Daniel and his colleagues are also employing cutting-edge techniques, like acoustic emission spectroscopy and X-ray diffraction, to gain a theoretical understanding of what causes materials inside a working battery to break down and eventually fail. "These tools give us the ability to measure the stress being experienced by battery components with X-rays and actually to listen to cracks forming in the components as they degrade," says Daniel. "By analyzing these noise events and correlating them with the X-ray diffraction data, we hope that we can determine what caused them to occur. My graduate student assistant, Kevin Rhodes, is doing a tremendous job with the collection and interpretation of those signals." This research is being conducted in cooperation with Edgar Lara-Curzio, Director of ORNL's High Temperature Materials Laboratory, and battery expert, Nancy Dudney.
Daniel hopes to use this information, along with traditional knowledge of fatigue properties of materials, to develop theories that explain how battery materials degrade and fail. "If we can do that, we can achieve a breakthrough in ways to create materials that last longer and work better," he says.
ORNL has worked closely with industry in the ongoing efforts to develop new battery technologies.
"We work with industry on almost every project," says Blue. "Much of our work culminates in new processes and parts.
Blue continues,"We can take advantage of the laboratory's basic research capabilities to give us the understanding of the materials. Then we can work with industry in the applied world. We like to believe that we are the best at what we do. The Laboratory has more than 140 R&D 100 Awards, 40 percent of which come out of the Lab's materials research programs."
The question for Blue and his colleagues —and for the automotive industry —is whether these capabilities will relieve the collective anxiety of the American public.
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