The rise of electric vehicles is threatening supplies of a host of the earth’s elements. Cobalt and lithium for batteries are getting most of the attention, but rare earths for electric motors are also a pinch point.
Now, Toyota Motor scientists have developed a new recipe for the motors’ permanent magnets that cuts reliance on particularly rare rare earths.
Permanent magnets keep electric motors turning in all kinds of devices, from electric toothbrushes to refrigerator compressors. In electric vehicles, the magnets need to last a long time without demagnetizing. They also have to stay stable at temperatures that can reach 100 ºC.
To meet those requirements, the magnets are made up of 30% rare earths, to take advantage of their many unpaired electrons, and 70% iron. The go-to rare earth for powerful, durable magnets is neodymium.
Most of this pricey element comes from China, and Toyota says demand is expected to increase rapidly. Smaller amounts of terbium or dysprosium are added to neodymium to lend heat resistance, but those elements are even more expensive.
Toyota has already cut terbium and dysprosium use in the 2016 Prius, and future magnets won’t use any, the firm promises. In addition, up to 50% of the neodymium will be replaced with the low-cost rare earths lanthanum and cerium.
To make the new recipe work, Toyota scientists reduced the size of the magnet’s grains to 0.25 micrometers, one-tenth their original size. They then concentrated neodymium on the surfaces of the smaller grains; the grains in standard magnets have the expensive element throughout. Looking inside the grains, they found that a 1:3 ratio of lanthanum to cerium is needed to prevent magnet performance from deteriorating.
Toyota says the new magnets could reach the market in the first half of the 2020s. They could also be used in robots and household appliances.
Lanthanum and cerium are low-cost rare earths.
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Ke Han, a research scientist at the U.S. National High Magnetic Field Laboratory, says Toyota is on the right path to reduce rare earths in permanent magnets. “I think it does take both approaches to do it—replacing some neodymium and reducing the grain size.”
Han would like to go even further. “Most rare earths are not very stable, even at room temperature,” he points out, and removing them completely would result in electric vehicles that last longer. Han is working on combinations of new materials, including manganese and gallium, but says developing non-rare-earth magnets will take years.
Another approach is to skip the permanent magnets entirely. Tesla Motors uses an electric induction motor, which was invented by Nikola Tesla and is aided by electromagnets instead.