Tesla announced today at its investor day that the company will build a rare-earth-free permanent magnet electric vehicle motor.
Rare earths are a bone of contention in the electric vehicle supply chain because supplies are difficult to secure and much of the world’s production is made or processed in China.
This is important for several reasons, not the least of which is the Biden administration’s current drive to produce materials for domestic electric vehicle components.
However, there are many misconceptions about what REE are and how much REE is used in electric vehicles. In fact, lithium-ion batteries generally do not contain rare earths (although they do contain other “critical minerals” as defined by the Inflation Reduction Act).
In the periodic table, “rare earths” are the elements highlighted in red in the diagram below – the lanthanides, as well as scandium and yttrium. In fact, they are not particularly rare either, with neodymium for about two-thirds of the copper content.
Rare earth elements in electric vehicles are used in electric vehicle motors, not batteries. The most commonly used is neodymium, a powerful magnet used in speakers, hard drives and electric motors. Dysprosium and terbium are commonly used additives for neodymium magnets.
Also, not all types of electric vehicle motors use REEs—Tesla uses them in its permanent magnet DC motors, but not in its AC induction motors.
Initially, Tesla used AC induction motors in its vehicles, which did not require rare earths. Actually, this is where the name of the company came from – Nikola Tesla was the inventor of the AC induction motor. But then when the Model 3 came out, the company introduced a new permanent magnet motor and eventually started using them in other vehicles.
Tesla said today that it has been able to reduce the amount of rare earths used in these new Model 3 powertrains by 25% between 2017 and 2022 thanks to improved powertrain efficiency.
But now it seems that Tesla is trying to get the best of both worlds: a permanent magnet motor but no rare earths.
The main alternative to NdFeB for permanent magnets is simple ferrite (iron oxide, usually with additions of barium or strontium). You can always make permanent magnets stronger just by using more magnets, but the space inside the motor rotor is limited and NdFeBB can provide more magnetization with less material. Other permanent magnet materials on the market include AlNiCo (AlNiCo), which performs well at high temperatures but loses magnetization easily, and Samarium Cobalt, another rare earth magnet similar to NdFeB but better at high temperatures. A number of alternative materials are currently being researched, mainly aimed at bridging the gap between ferrites and rare earths, but this is still in the lab and not yet in production.
I suspect that Tesla found a way to use a rotor with a ferrite magnet. If they reduced the REE content, that meant they were reducing the number of permanent magnets in the rotor. I bet they decided to get less than usual flux from a large piece of ferrite instead of a small piece of NdFeB. I may be wrong, they may have used an alternative material on an experimental scale. But that seems unlikely to me – Tesla is aiming for mass production, which basically means rare earths or ferrites.
During the investor day presentation, Tesla showed a slide comparing the current use of rare earths in the Model Y permanent magnet motor with a potential next-generation motor:
Tesla didn’t specify which elements it used, possibly believing the information to be a trade secret it didn’t want to divulge. But the first number can be neodymium, the rest can be dysprosium and terbium.
As for future engines – well, we’re not really sure. Tesla’s graphics suggest that the next generation motor will contain a permanent magnet, but that magnet will not use rare earths.
Neodymium-based permanent magnets have been the standard for such applications for some time, but other potential materials have been explored over the past decade to replace it. While Tesla hasn’t specified which one it plans to use, it looks like it’s close to making a decision – or at least sees an opportunity to find a better solution in the near future.
Jameson has been driving electric vehicles since 2009 and has been writing about electric vehicles and clean energy for electrok.co since 2016.
Post time: Mar-08-2023