Axial Flux Motors

An edited extract from a longer analysis by Dr. Jon Hykawy.

​Rare earth magnets were first developed in the late 1960s, with samarium and cobalt in the first versions developed by elements of the US military. Those magnets were good but expensive. Neodymium, iron and boron magnets were developed in the 1980s. Rare earth-based magnets are much stronger permanent magnets than anything else we have developed, to date. This means that electric motors using permanent, rare earth magnets are smaller and lighter than any alternatives producing the same amount of power.
 
The results have been stunning. Those small and efficient electric motors have allowed development of electric drone aircraft and battery-powered electric vehicles, products that all of us have become familiar with over the last 10 years. These magnets have become so ubiquitous that we don’t even think about developments such as tiny, but powerful, speakers, earphones and the like, all enabled by these powerful magnets.
 
There are two main drawbacks to the use of rare earth magnets. First, the magnets we usually refer to as ‘rare earth magnets’ are a particular crystal structure of Nd2Fe14B. We refer to them as ‘neodymium’ magnets, even though most of their mass is iron. Those magnets are prone to losing field strength as the temperature goes up (eventually losing their magnetic field, permanently and altogether). To delay this effect to higher temperatures, the magnets alloy in even less common rare earths, like dysprosium (Dy) and terbium (Tb). But those rare earths are expensive and difficult to obtain. Second, almost all investors are aware that rare earth processing and production are dominated by Chinese firms, mostly state-owned enterprises. This has become such a concern that even the President of the United States tried to forge a critical minerals deal with Ukraine, for access to such materials as rare earth, during the first year of this current administration. Western nations are actively seeking new, non-Chinese sources of rare earths, especially rare earths like Dy and Tb that are hard to get.
 
But all the above presupposes that the technology we have, today, is the technology that will carry us forward into the future. And the one absolute truth about technology is that the state-of-the-art is always evolving. There is a (relatively) new technological development that is important for any investor interested in rare earth to understand, because it bears on both the quantity and types of rare earths needed by users such as the automotive sector. That change is the (re?)advent of the axial flux electric motor.
 
New axial flux electric motors, exemplified by the offerings from Mercedes subsidiary YASA, are much smaller and lighter than conventional radial flux electric motors using neodymium permanent magnets. While still expensive, owing to some fairly stringent design specifications for components within them directly coupled to a lack of scale in manufacturing those components, the axial flux design has a couple of advantages that the radial flux motor can’t match.
 
Most importantly, from a critical materials perspective, axial flux motors are much easier to keep cool than their radial flux cousins. While they use roughly the same amount of magnet material as radial flux motors, the amount of magnet being directly related to power production, axial flux motors can maintain peak power for longer before overheating. It is also possible to substitute neodymium magnets that contain much less of the expensive, and truly rare, rare earths, like Dy and Tb, that allow neodymium magnets to maintain their strength at elevated temperatures. Indeed, there’s even work being done that suggests axial flux motors could be built using ferrite magnets or electromagnets. This would remove the need for rare earth, altogether, without sacrificing performance or size. That could produce a cost saving that might even justify the axial flux motor over radial flux motors on purely economic grounds. And this might be bad news for the nascent western rare earth industry.
 
Our lesson from this piece is simple, albeit speculative. Today, axial flux electric motors are being used in specialty applications, like sports cars, where weight but, especially, physical size matters more than cost. However, axial flux motor cost depends on the cost of specialty components like carbon fibre rotors, items that will decline, with time and scale, in cost. From a raw material perspective, axial flux motors use a lot less steel, aluminum and copper than radial flux motors, for a given power and torque output.
 
Many western governments are scrambling to secure supplies of rare earths, to ensure sufficient supply for needed electric motors. Investors seem happy to provide the financing to these companies, given what looks like inevitable demand growth. However, it seems just as important to consider the potential for new technologies that could reduce or eliminate the need for these critical materials.

If you would like access to the full version please contact us via [email protected].