Japanese carmaker develops world's first neodymium-reduced, heat-resistant magnet, which is a key element of the foundation required to popularise electrified vehicles.
20 Feb 2018 | 3604 Views | By Autocar Pro News Desk
Toyota Motor Corporation has developed the world's first neodymium-reduced, heat-resistant magnet. Neodymium magnets are used in various types of motors such as the high-output motors found in electrified vehicles, use of which is expected to increase rapidly in the future. The new magnet uses significantly less neodymium, a rare-earth element, ...
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Toyota Motor Corporation has developed the world's first neodymium-reduced, heat-resistant magnet. Neodymium magnets are used in various types of motors such as the high-output motors found in electrified vehicles, use of which is expected to increase rapidly in the future. The new magnet uses significantly less neodymium, a rare-earth element, and can be used in high-temperature conditions.
The newly developed magnet uses no terbium (Tb) or dysprosium (Dy), which are rare earths that are also categorized as critical materials(3) necessary for highly heat-resistant neodymium magnets. A portion of the neodymium has been replaced with lanthanum (La) and cerium (Ce), which are low-cost rare earths, reducing the amount of neodymium used in the magnet.
Neodymium plays an important role in maintaining high coercivity (the ability to maintain magnetisation) and heat resistance. Merely reducing the amount of neodymium and replacing it with lanthanum and cerium results in a decline in motor performance. Accordingly, Toyota says it adopted new technologies that suppress the deterioration of coercivity and heat resistance, even when neodymium is replaced with lanthanum and cerium, and developed a magnet that has equivalent levels of heat resistance as earlier neodymium magnets, while reducing the amount of neodymium used by up to 50 percent.
This new type of magnet is expected to be useful in expanding use of motors in various areas such as automobiles and robotics, as well as maintaining a balance between the supply and demand of valuable rare earth resources. Toyota will work to further enhance performance and evaluate application in products while accelerating the development of mass production technologies, with the aim of achieving early adoption in motors used for various applications, including in automobiles and robotics.
Development of elemental technologies for motors, inverters, batteries, and other components will require steady research and development in anticipation of the future. Toyota positions these technologies as essential for electrified vehicles and will continue making steady progress in each and every area, while working to build the foundation that will support the increased use of electrified vehicles in the future.
Development of the Nd-reduced, heat-resistant magnet
It is important that magnets used in automotive motors and other applications have high coercivity (the ability to maintain magnetisation) even at high temperatures. For this reason, approximately 30 percent of the elements used in magnets are rare earths.
When powerful neodymium magnets are used at high temperatures, such as for automotive applications, terbium and dysprosium are generally added to increase high-temperature coercivity. However, terbium and dysprosium are rare and expensive metals found in locations with high geopolitical risks. Because of this, considerable efforts have been made to develop magnets that do not use these metals, and positive results have been achieved.
Production volumes of neodymium are relatively high among rare earths, but there are concerns that shortages will develop as electrified vehicles, including hybrid and battery electric vehicles, become increasingly popular in the future. Despite this, little effort has been made to address neodymium use.
To overcome these issues, Toyota says it successfully undertook development of technologies that can both eliminate the use of terbium and dysprosium and reduce the amount of neodymium used. Through substitution of neodymium with lanthanum and cerium, which are abundant and low-cost rare earths, high heat resistance can be maintained and loss of coercivity minimised.
Use of rare earths in neodymium magnets
The newly developed Nd-reduced, heat-resistant magnet is able to maintain coercivity even at high temperatures because of the combination of the following three new technologies:
Grain refinement of magnet: It is now possible to retain high coercivity at high temperatures through the reduction of the size of the magnet grains to one-tenth or less of those found in conventional neodymium magnets and the enlargement of the grain boundary area.
Two-layered high-performance grain surface: In a conventional neodymium magnet, neodymium is spread evenly within the grains of the magnet, and in many cases, the neodymium used is more than the necessary amount to maintain coercivity. Thus, it is possible to efficiently use neodymium by increasing the neodymium concentration on the surface of the magnet grains, which is necessary to increase coercivity, and decreasing the concentration in the grain core. This results in the reduction of the overall amount of neodymium used in the new magnet.
Specific ratio of lanthanum and cerium: If neodymium is simply alloyed with lanthanum and cerium, its performance properties (heat resistance and coercivity) decline substantially, complicating the use of light rare earths. As a result of the evaluation of various alloys, Toyota discovered a specific ratio at which lanthanum and cerium, both abundant and low-cost rare earths, can be alloyed so that the deterioration of properties is suppressed.
World's first Nd-reduced, heat-resistant magnet developed by simultaneously incorporating all three technologies
Heat resistance performance.
Electron microscope image and composition analysis mapping image.
Future efforts
The new Nd-reduced, heat-resistant magnet developed at this time not only eliminates the use of terbium and dysprosium, rare earths necessary for neodymium magnets that require high heat resistance, but it also reduces the amount of neodymium used. This new magnet is expected to have a wide range of applications in motors that require relatively high output such as those required for electrified vehicle drive motors and generators, electric power steering, robots, and various household appliances. It will also contribute to reducing the risks of a disruption in supply and demand of rare earths and price increases.
Going forward, Toyota will proceed with further practical use in mind, perform application assessments in motor vehicles, and continue researching and developing technologies with the aim of low-cost, stable production.
Toyota expects that the magnets will be put to use in the motors of electric power steering for automobiles and other applications in the first half of the 2020s. Furthermore, the company will undertake development with the aim of practical application in high-performance electrified vehicle drive motors within the next 10 years.