65 Motor materials | Product focus E-Mobility Engineering | May/June 2025 efficiency increases of 1–2 percentage points owing to the thinner insulation leading to an increased fill factor and lower thermal resistance. This impacts motor design, the battery pack and the entire system, enabling more compact, lighter, cost-effective and sustainable designs with potential for downsized batteries for equal range. Imperatives of mass production As production volumes rise, scalability and cost-effectiveness become critical, bringing their own set of material tradeoffs. Rare earth magnets, high-grade electrical steel and advanced alloys, for example, can all be expensive, making material substitution and recycling attractive options where available. Volume production focuses attention on design for manufacturability and automation, often penalising complex motor designs and the use of highly specialised materials. At the same time, diversifying material sources and developing recycling infrastructure become increasingly vital to supply chain security and sustainability. Supply chain security With increasing geopolitical uncertainty, the supply chain security of critical raw materials, particularly those used in high-performance permanent magnets, is a growing concern. Heavy reliance on imports of these materials or their precursors poses a potential threat to the future development of high-efficiency motors, especially in regions with limited domestic resources. To mitigate this risk, significant efforts are being directed toward establishing local capabilities for recycling and processing end-of-life magnetic materials. The goal is to create a circular economy for these critical components, ensuring a more stable and sustainable supply. Finding suitable alternatives to rare earth magnets that offer comparable performance is a major challenge, as is the development of cost-effective and environmentally friendly processes for their recycling. Furthermore, improving the temperature stability of magnetic materials for high-temperature applications is also exercising the ingenuity of materials scientists and engineers. Magnetic attraction Rare earth permanent magnets create strong magnetic fields that are crucial for achieving high power density and efficiency. These strong magnetic fields contribute to lower conductive (‘copper’) losses by reducing the current needed to generate a specified amount of torque. In particular, neodymium-iron-boron (NdFeB) magnets exhibit high magnetic remanence and coercivity that reduce electrical losses in the stator and enable motors to operate more efficiently, even at partial loads. While alternatives to rare earth magnets, such as ferrite magnets, are cheaper and offer better intrinsic temperature stability and corrosion resistance, they typically exhibit lower magnetic performance and lack the high remanence or energy production crucial for efficient e-motors. Today, sintered NdFeB magnets are the standard used in e-motor with that of air, also contribute to more effective heat dissipation from the motor core. (For more on cooling, see the feature starting on page 42.) Chasing efficiency The pursuit of higher motor efficiency is constrained by several limitations imposed by available materials. A primary challenge lies in maximising the packaging density of the motor’s core components, namely the laminated rotor and stator stacks, as well as the copper windings in the stator. Existing insulation coatings on electrical steel sheets, sometimes made as adhesive layers used to bond these sheets together, introduce a physical barrier that limits how tightly the laminations can be packed. Similarly, the insulation around copper wiring and the required spacing between windings impact the achievable density in the stator. Ongoing research is focused on developing adhesive systems capable of achieving ultra-thin bond-line thicknesses while maintaining high bond strength and exhibiting rapid curing times. Beyond packaging density, the temperature stability of permanent magnetic materials at elevated operating temperatures presents a substantial hurdle. As motors become more powerdense, their magnets are subjected to substantial heat. Maintaining magnetic performance at such temperatures is crucial for sustained efficiency and reliability. Furthermore, the formation of eddy currents within the electrical steel contributes to energy losses, necessitating use of materials with inherently lower eddy current susceptibility. One of the most significant material limitations hindering higher-efficiency motors designed for e-mobility is electrical insulation. Traditional slot liner materials such as aramid paper and wire coating materials like enamels have not evolved at the same pace as e-motor design. Thermoplastic solutions for both slot and wire insulation are being developed to address this mismatch, experimentally demonstrating Potting compound used here to encapsulate stator windings in a motor case, primarily ensures a good thermal connection between the windings and the case for efficient heat transfer, and also provides some physical protection (Image courtesy of Parker Lord)
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