Lightweighting is a common goal for electric vehicles, drones and spacecraft. Lighter machines consume less energy, helping their batteries work more efficiently and allowing them to fly longer distances. Lightweighting also goes hand-in-hand with sustainability, as better overall performance leads to lower carbon emissions. Electric motors are at the heart of this effort. Motor coils make up a large portion of a motor's weight, and most coils use copper. Copper conducts electricity well, but it also poses some challenges, such as resource supply issues, price fluctuations, and increased weight due to high density.
A team led by Dr. Dae-Yoon Kim at the Institute of Composite Materials at the Korea Institute of Science and Technology (KIST) has developed an electric motor with coils made only of carbon nanotubes (CNTs), without any metal. In tests, the team was able to control the motor's revolutions per minute (RPM) based on changes in input voltage. This shows that electric motors can perform their basic function of converting electrical energy into rotational force without the use of metallic conductors.
Carbon nanotubes (CNTs) are one-dimensional tubular nanomaterials with carbon atoms arranged in a hexagonal honeycomb structure. They are much lighter than ordinary metals and have high electrical conductivity, strong mechanical strength and good thermal conductivity. Even so, CNTs still face many challenges in practical applications. One major problem is catalyst metal leftover from the manufacturing process. These metal particles can directly affect motor components by adhering to the CNT surface and reducing electrical performance.
The KIST team developed a new carbon nanotube (CNT) purification process that exploits the orientation behavior of liquid crystals, the "fourth state of matter" between liquid and solid states. As the carbon nanotubes orient, the process naturally breaks down the clumps and helps remove metal particles from the surface. The key is that it can selectively remove impurities without damaging the nanostructure of the carbon nanotubes. This makes it different from many liquid and gas phase purification methods. The resulting carbon nanotubes are more conductive enough to work in actual electric motors.
The researchers then made coils from purified carbon nanotubes and ran motors that exhibited stable speed control at different voltages. If this approach can be scaled, lighter coils could reduce motor weight and overall system mass. It could also reduce reliance on copper and lower price and supply risks. Future research is needed to compare the performance of copper-based designs in terms of power density, efficiency, thermal handling, and cost under actual operating conditions.
Dr. Kim Dae-yun of Korea Institute of Science and Technology said: "By developing unprecedented new concept CNT high-quality technology, we can maximize the electrical performance of CNT coils to drive metal-free motors. Based on the innovation of CNT materials, we will be the first to localize materials such as battery conductive materials, semiconductor films, and robot cables."
Source: KIST