The electric vehicle revolution has created market forces to drive all sorts of innovations. Battery technology has progressed at a rapid pace, and engineers have developed ways to charge vehicles at ever more breakneck rates. Similarly, electric motors have become more powerful and more compact, delivering greater performance than ever before.

In the latter case, while modern EV motors are very capable things, they’re also reliant on materials that are increasingly hard to come by. Most specifically, it’s the rare earth materials that make their magnets so good. The vast majority of these minerals come from China, with trade woes and geopolitics making it difficult to get them at any sort of reasonable price. Thus has sprung up a new market force, pushing engineers to search for new ways to make their motors compact, efficient, and powerful.

Rare

Rare earth materials have become a hot button issue in recent decades, and they’ve also become a familiar part of our lives. If you remember playing with some curiously powerful magnets at some point, you’ve come across neodymium—a rare earth material of wide application. The element is alloyed with iron and boron to produce some of the strongest magnets readily available on the commercial market. You’ll find them in everything from hard drives to EV motors, and stuck to a great many fridges, where they’re quite hard to peel off. At times, neodymium is also alloyed with other rare earths, like terbium and dysprosium, which can help create powerful magnets that are able to resist higher temperatures without failure.

We come across these magnets all the time, so they might not feel particularly rare. Indeed, the rare earth elements—of which there are 17 in total—are actually fairly abundant in the Earth’s crust. The problem is that they are thinly spread, often only found as trace elements rather than in rich ore deposits that are economical to mine. Producing any useful amount of rare earth materials tends to require processing a great deal of raw material at significant cost. As it stands, China has gained somewhat of a monopoly on rare earths, controlling up to 92% of global processing capability and 60 to 70% of mining capacity. In happier times, this wouldn’t be such a problem. Sadly, with the extended battles being fought over global trade at the moment, it’s making access to rare earths both difficult and expensive.

This has become a particular problem for automotive manufacturers. It’s no good to design a wonderful motor that needs lots of fancy rare earth magnets, only to find out a year later that they’re no longer available and that production must shut down. Thus, there is a serious desire on the part of major automakers to produce high-performance motors that don’t require such fancy, hard-to-come-by materials. Even if they come with a small cost penalty in materials or manufacturing, they could save huge sums of money if they avoid a production shutdown at some point in the future. Large manufacturing operations are slow, lumbering things that need to run on long timescales to operate economically, and they can easily be derailed by supply disruptions. Securing a solid motor supply is thus key to companies looking to build EVs en masse in the immediate future.

BMW has, to a degree, solved the problem by making different kinds of motors. Rather than trying to find other ways to make powerful magnets, the German automaker put engineering efforts into developing highly-efficient motors that generate their own magnetic fields via electricity. Instead of using permanent magnets on the rotor, they use coils, which are electrically excited to generate a comparable magnetic field. Thus, rare earth magnets are replaced with coil windings, which are much easier to source. These motors are referred to as Electrically Excited Synchronous Motors (EESM), and are distinct from traditional induction motors as they are creating a magnetic field in the rotor via supplied electric current rather than via induction.

This method of construction does come with some trade offs, of course, such as heat generated by the rotor coils, and the need for slip rings or brushes to transfer power to the coils on the rotor. However, they manage to neatly sidestep the need for rare earth materials entirely. They are also more controllable. Since it’s possible to vary the magnetic field in the rotor as needed, this can be used to make efficiency gains in low-load situations. They’re also less susceptible to damage from overtemperature that could completely destroy the magnets in a permanent magnet motor.

BMW was inspired to take this route because of a spike in neodymium prices well over a decade ago. Today, that decision is bearing fruit—with the company less fearful of supply chain issues and production line stoppages due to some pesky magnets. You’ll find EESM motors in a range of BMW products, from the iX1 to the i7, and even the compact CE 02 scooter. The company’s next generation of electric models will largely use EESM motors for rear-wheel-drive models, while using asynchronous motors up front to add all-wheel-drive to select models. The German automaker is not the only player in this space, either. A range of third-party motor manufacturers have gotten on board the EESM train, as well as other automakers like Nissan and Renault.

Nissan has similarly gotten onboard with EESM technology. Note the contact surfaces for the brushes used to deliver electricity to the coils in the motor.

Don’t expect every automaker to rush into this technology overnight. Retooling production lines to make different types of motors takes time, to say nothing of the supporting engineering required to control the motors and integrate them into vehicle designs. Many automakers will persevere with permanent magnet motors, doing what they can to secure rare earth supplies and shore up their supply chains. However, if the rare earth crisis drags on much longer, expect to see ever more reliance on new motor designs that don’t need rare earth magnets at all.