Toyota unveils plans to slash heavy rare earth use in EV motors

Published: Thursday, 29 March 2018

Neodymium is reduced, dysprosium and terbium eliminated, and sources outside China can be opened up, the Japanese carmaker says.

Car manufacturer Toyota has unveiled a method to halve the amount of neodymium used in heat-resistant permanent magnets, and to entirely avoid the use of the heavy rare-earth elements terbium and dysprosium.

The technology would give magnet-makers the option of sourcing their materials from somewhere other than China, and could ease the soaring demand in the electric vehicle (EV) sector for traditional magnet rare-earth materials, while increasing demand for cerium and lanthanum.

The technology would "contribute to reducing the risks of a disruption in supply and demand of rare earths, and price increases," Toyota said.

The company expects that the new magnet technology will be brought into commercial use in the "first half of the 2020s," with use in EV motors "within the next 10 years."

Materials used in the magnet, including the rare earths.

Rising neodymium demand

Electric-vehicle makers have become increasingly concerned about the need to use rare-earth permanent magnets in their motors, because they offer better power-to-weight performance than electromagnets.

These magnets are considered essential if EVs are to deliver the longer driving ranges that vehicle buyers demand, but they expose manufacturers to rising material costs and the threat of disruptions to the supply chain.

The most common type of magnet in commercial use is made of iron and boron, alloyed with the light rare-earth neodymium.

Neodymium magnets have long been the most affordable, as well as the strongest, type of rare-earth magnet. But the prices for neodymium have been increasing rapidly while demand for such magnets has increased, driven by the EV industry, as well as for use in generators in wind turbines.

"Production volumes of neodymium are relatively high among rare earths, but there are concerns that shortages will develop when electrified vehicles, including hybrid and battery electric vehicles, become increasingly popular in the future," Toyota said.

A fourth generation Prius motor.

Maintaining effectiveness

In addition, neodymium magnets lose their effectiveness when exposed to high temperatures, which has the effect of reducing engine performance in EV applications.

One solution to this loss in performance is the addition of heavy rare-earth elements such as terbium and dysprosium. But this solution brings up fresh difficulties of supply.

Heavy rare-earth elements are currently only produced in China, although Australia’s Northern Minerals plans to commence pilot production of terbium and dysprosium in 2018.

"Terbium and dysprosium are rare and expensive metals, found in locations with high geopolitical risks," Toyota said.

Toyota has already achieved a significant reduction in the amounts of terbium and dysprosium used in its electric engine for the fourth-generation Prius, its hybrid vehicle. But this reduction was achieved at the cost of even higher neodymium use.

This new technology, in contrast, not only eliminates the remaining heavy rare earths, but trades a portion of the neodymium for lanthanum or cerium.

Crystallized grains

Neodymium magnets consist of tiny crystallized magnet grains. The new magnet technology reduces the size of the magnet grains, in order to preserve coercivity, which is the ability of the material to hold magnetization.

The new production process also results in grains which have high concentrations of neodymium on the surface, while the core of each grain is composed of a cheaper mixture of lanthanum and neodymium.

"If neodymium is simply alloyed with lanthanum and cerium, its performance properties [such as heat resistance and coercivity] decline substantially, complicating the use of light rare earths," Toyota said.

"As a result of the evaluation of various alloys," it added, "Toyota has 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."

Range of applications

The new technology will perform as well as more traditional rare-earth magnets, with equivalent heat resistance, Toyota said, but with as much as half of the neodymium replaced with lower-priced lanthanum and cerium.

"This new magnet is expected to have a wide range of applications in motors that require relatively high output," Toyota said, "such as those required for EV drive motors and generators, electric power steering, robots, and various household appliances."