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Whether it's electric vehicles, drones, or spacecraft, a common technical challenge for future transportation is lightweighting.

Reducing the weight of a vehicle not only reduces energy consumption, but also increases battery efficiency and increases range. This is considered a key technology that is directly linked to sustainability, as it improves the performance of the system as a whole and thus contributes to reducing carbon emissions.

Electric motors in particular are an essential component of most electric mobility vehicles, and coils account for a large proportion of the total weight of the motor.

Until now, metals such as copper have been used as the main material for coils due to their high electrical conductivity, but it has been consistently pointed out that they have various limitations, such as difficulty in securing resources, price volatility, and weight problems due to high density.

Dr. Dae-Yoon Kim and his team at the Korea Institute of Science and Technology (KIST) Composite Materials Research Institute have succeeded in constructing the coil of an electric motor using only carbon nanotubes (CNTs) without any metals, and realizing it to the point where it can actually run.

The team conducted experiments by applying the coil made of CNTs to the motor and found that the revolutions per minute (RPM) of the motor could be stably controlled according to the input voltage. This demonstrates that the basic operation of a motor, which converts electrical energy into mechanical rotational force, can be accomplished without metal.

The work is in the journal Advanced Composites and Hybrid Materials.

CNTs are one-dimensional tube-shaped nanomaterials with carbon atoms arranged in a hexagonal honeycomb structure, which are known to be much lighter than ordinary metals, while at the same time possessing excellent electrical conductivity, mechanical strength, and thermal conductivity.

These properties have long attracted attention as a next-generation material, but CNTs have faced a number of barriers to real-world industrial applications.

One of the technical obstacles is the residue of catalyst metals used during the manufacturing process. These remain as metallic particles on the surface of CNTs, degrading their electrical properties, which are directly related to motor performance, making it difficult to utilize CNTs in high-performance components.

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The team has developed a new CNT purification process that utilizes the alignment principle of liquid crystals, a "fourth state of matter" known as the intermediate state between liquid and solid. The process naturally resolves strong aggregation during the alignment of CNTs, effectively removing metallic particles that remain on the surface.

Most importantly, it is able to selectively remove impurities without damaging the nanostructure of the CNTs, making it distinctly different from existing liquid- and gas-phase-based purification methods. The purified CNTs show a significant improvement in conductivity, which can be brought to a level that can be applied to actual electric motors.

"By developing a new concept of high-quality CNT technology that has never existed before, we were able to maximize the electrical performance of CNT coils to drive electric motors without metal," said Dr. Dae-Yoon Kim of KIST.

"Based on the innovation of CNT materials, we will take the lead in localizing materials such as conductive materials for batteries, pellicles for semiconductors, and cables for robots."