Experimental motors use exotic materials and clever configurations

THE DILEMMA IS EASY to describe. Global efforts to combat climate change hinge on pivoting sharply away from fossil fuels. To do that will require electrifying transportation, primarily by shifting from vehicles with combustion engines to ones with electric drive trains. Such a massive shift will inevitably mean far greater use of electric traction motors, nearly all of which rely on magnets that contain rare earth elements, which cause substantial environmental degradation when their ores are extracted and then processed into industrially useful forms. And for automakers outside of China, there is an additional deterrent: Roughly 90 percent of processed rare earth elements now come from China, so for these companies, increasing dependence on rare earths means growing vulnerability in critical supply chains.

Against this backdrop, massive efforts are underway to design and test advanced electric-vehicle (EV) motors that do not use rare earth elements (or use relatively little of them). Government agencies, companies, and universities are working on this challenge, oftentimes in collaborative efforts, in virtually all industrialized countries. In the United States, these initiatives include long-standing efforts at the country’s national laboratories to develop permanent magnets and motor designs that do not use rare earth elements. Also, in a collaboration announced last November, General Motors and Stellantis are working with a startup company, Niron Magnetics, to develop EV motors based on Niron’s rare earth–free permanent magnet. Another automaker, Tesla, shocked observers in March of last year when a senior official declared that the company’s “next drive unit,” which would be based on a permanent magnet, would nevertheless use no “rare earth elements at all.” In Europe, a consortium called Passenger includes 20 partners from industry and academia working on rare earth–free permanent magnets for EVs.

We have been working for nearly a decade on magnetic and other aspects of traction-motor design at Oak Ridge National Laboratory (ORNL), in Tennessee, a hub of U.S. research on advanced motors for EVs. Along with colleagues from the National Renewable Energy Laboratory, Ames Laboratory, and the University of Wisconsin, Madison, we have been studying advanced motor concepts as part of the U.S. Department of Energy’s U.S. Drive Technologies Consortium. The group also includes Sandia National Laboratories, Purdue University, and the Illinois Institute of Technology.

With all of this activity, you would think that engineers would have by now developed a sophisticated understanding of what is possible with rare earth–free electric motors. And indeed they have. We and other researchers are evaluating promising permanent-magnet materials that don’t use rare earth elements, and we are evaluating possible motor-design changes required to best use these materials. We are also evaluating advanced motor designs that do not use permanent magnets at all. The bottom line is that replacing rare earth–based magnets with non–rare earth ones comes at a cost: degraded motor performance. But innovations in design, manufacturing, and materials will be able to offset—maybe even entirely—this gap in performance. Already, there are a few reports of tantalizing results with innovative new motors whose performance is said to be on a par with the best permanent-magnet synchronous motors.

Why rare earths make the most powerful electric motors

Rare earth elements (which people in our line of work often refer to as REEs) have unique properties that make them indispensable to many forms of modern technology. Some of these elements, such as neodymium, samarium, dysprosium, and terbium, can be combined with ferromagnetic elements such as iron and cobalt to produce crystals that are not only highly magnetic but also strongly resist demagnetization. The metric typically used to gauge these important qualities of a magnet is called the maximum energy product, measured in megagauss-oersteds (MGOe). The strongest and most commercially successful permanent magnets yet invented, neodymium iron boron, have energy products in the range of 30 to 55 MGOe.

For an electric motor based on permanent magnets, the stronger its magnets, the more efficient, compact, and lightweight the motor can be. So the highest-performing EV motors today all use neodymium iron boron magnets. Nevertheless, clever motor design can reduce the performance gap between motors based on rare earth permanent magnets and ones based on other types of magnets. To understand how, you need to know a little more about electric motors.

This article first appeared at IEEE Spectrum on July 2, 2024.