Tesla’s announcement of designing a rare-earth-free permanent-magnet motor has stunned the industry. What technology could possibly compete with the strongest magnet on the market?
Colin Campbell, director of drive-train engineering at Tesla, dropped quite the bombshell at Tesla’s investor day on 1 March. “We’ve designed our next drive unit, which uses a permanent-magnet motor, to not use any rare-earth elements at all,” he announced. Tesla had previously reported a 25 percent reduction of rare-earth content in Model 3 and Model Y drive trains. Further trimmings were expected, but few would have thought it possible that a rare-earth-free permanent-magnet motor was close to commercial application.
Tesla’s earliest models used an induction motor, in which the magnetic force that causes the rotor to turn is generated by an alternating current. The Model 3, introduced in 2017, adopted motors in which strong permanent magnets are used to generate the magnetic field. Permanent-magnet (PM) motors offer greater efficiency and power density. In 2022, over 80 percent of the electric vehicle motor market was accounted for by PM motors, according to research by IDTechex.
Nonetheless, carmakers are keen to reduce their dependence on rare earths for making strong magnets. Many still use the powerful alloy of iron, boron and the rare earth neodymium (NdFeB). More rare earths can be added to fine-tune or enhance properties. China’s tight grip on the supply of these materials is a liability to the car industry, especially now that a rift is growing between Beijing and Washington. China mines about two-thirds of the world’s annual demand for rare earths, and refines an even higher percentage.
Additionally, rare-earth prices are a major concern. In the past, they’ve been subject to wild swings and in the future, they may climb uncomfortably high as the world pivots toward electrification and sustainable energy sources such as windmills, which will drive up demand for strong magnets. “As the world transitions to clean energy, demand for rare earths is really increasing dramatically and not only is it going to be a little hard to meet that demand, mining rare earths has environmental and health risks,” Campbell explained.
Massive
The problem is physics. Neodymium and a few other rare earths have unique properties that enhance the magnetic properties of iron. There’s no substitute for them – rare-earth permanent magnets are the best on the market. Hence the confusion about Campbell’s announcement. Anything that Tesla has come up with would either have to take a hit on performance or be bulkier and heavier than the PM motor the company currently employs.
Adamas Intelligence, a research and advisory firm specializing in metals and minerals, expects the most likely candidate replacing NdFeB in Tesla’s next-generation motor is the ferrite magnet, which consists of iron oxide blended with various ceramic materials. “It’s a proven concept,” the consultancy writes, pointing to a motor design presented a few months ago by Japan’s Proterial (formerly Hitachi Metals).
But it’s not “a perfect alternative.” In simulations, Proterial’s ferrite-magnet motor matched the output and maximum rotation speed of a comparable motor using NdFeB magnets, but at a “massive” weight penalty of 30 percent. A second design matching output and weight but operating at a 50 percent higher rotation speed resulted in “a material reduction” in torque.
A less likely option would be the iron nitride magnet, in which added nitrogen atoms induce changes in the crystal structure of iron, boosting the magnetic properties. This technology is less mature than ferrite, but Niron Magnetics, a spinout of the University of Minnesota, says it’s close to launching a product that matches the performance of rare-earth magnets at a lower cost. The company is partnering with GM, however, not Tesla.
Main picture credit: Tesla