Korean researchers used carbon nanotubes to build a motor that’s five times lighter

A new study details how researchers successfully built and operated a motor using coils woven from pure carbon nanotubes instead of the heavy copper that has been the standard for a century. But can we actually replace the copper coils in our motors?

The world is getting lighter, or at least, it’s trying to. The main reason is efficiency. If you can make things lighter, you don’t need as much power to move them around. Shaving off a few kilograms makes for lighter vehicles that consume less energy, boast a longer range, and ultimately, have a lower carbon footprint. It’s a virtuous cycle.

However, a heavy problem has been holding us back: motors that are heavy and chunky. A lot of that weight comes from tightly wound coils of metal, usually copper. For a century, copper has been the undisputed king of conductivity, the go-to material for pushing electrons where we need them to go. But it’s a heavy crown to wear. Copper is dense, its price is volatile, and mining it carries a significant environmental cost.

Dr. Dae-Yoon Kim and his team at the Korea Institute of Science and Technology (KIST) think we can do better.

It’s not the first time something like this has been attempted. For years, scientists have dreamed of an alternative, a material that is both a featherweight and an electrical powerhouse. The dream material now has a name: carbon nanotubes. And the team in South Korea has moved them from the realm of fantasy to a functioning reality.

They built an electric motor where the hefty copper coils were completely replaced with threads spun from pure carbon nanotubes. And it works. When they hooked it up to a power source, the motor whirred to life, its rotational speed climbing steadily with the voltage. It was a successful demonstration that the fundamental principle of a motor — turning electrical energy into mechanical force — could be achieved without a single atom of metal in its coils.

A purity problem

Carbon nanotubes have been hailed as a wonder material. They’re already used to add strength to everything from high-end bicycle frames to aerospace parts, and to improve the performance of batteries. They consist of carbon atoms arranged in a hexagonal honeycomb pattern; these atoms are then rolled into a cylinder that measures a few nanometers across, a bit like a chicken wire. This unique structure makes them stronger than steel and lighter than copper. They’re also excellent conductors of heat and electricity.

The problem is purity. In order to maintain their desirable properties, carbon nanotubes need to be pure. The most common way to manufacture them uses tiny metallic particles, usually iron, as catalysts to kickstart the growth of the tubes. The problem is, after the process completes, some of these metallic troublemakers cling to the nanotubes’ surfaces like microscopic barnacles.

These impurities wreak havoc on the nanotubes’ electrical performance. They act like roadblocks for the flowing electrons and degrade its conductivity. For an application such as an electric coil, this is an absolute deal breaker. This is largely why previous attempts at creating nanotube motors failed. Cleaning them up proved to be a delicate, often destructive, process. Existing purification methods, which used harsh chemicals in liquid or gas form, were a bit like using a sledgehammer to crack a nut — they often damaged the pristine nanostructure of the tubes, compromising their very properties in the quest to clean them.

This is where the KIST team’s ingenuity shines. They needed a way to surgically remove the impurities without harming the nanotubes. And they found their solution in a strange and beautiful state of matter: liquid crystals.

Liquid what?

Often called the “fourth state of matter,” liquid crystals exist in a curious limbo between a liquid and a solid. They can flow like a liquid, but their molecules are arranged with some degree of order, like in a solid crystal. This unique property is what makes the screen on your laptop or TV work. Dr. Kim’s team realized they could harness this state to solve their purity problem.

The team developed a novel process they call “lyotropic liquid crystal-assisted surface texturing,” or LAST. It begins by dissolving a batch of raw, impure carbon nanotubes in something called chlorosulfonic acid. This super-acid coats the surface of each individual nanotube, causing them to repel each other and preventing them from clumping together. This forces the nanotubes into a perfectly dispersed, aligned state — the liquid crystal phase. Every single tube is separated, its entire surface exposed.

Then, they’re dropped into water. The water reacts with the acid, instantly creating hydrochloric acid right at the surface of the nanotubes. This freshly formed acid is a potent cleaning agent for the metallic impurities. It efficiently etches away the iron oxide particles, transforming them into water-soluble iron chloride, which can then be simply washed away. It’s an incredibly elegant process that doesn’t damage the delicate hexagonal lattice of the carbon nanotubes themselves.

“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.

The results were dramatic. When they examined the purified CNTs under a powerful microscope, the once-speckled surfaces were now immaculately clean. The electrical conductivity of the material skyrocketed by 133%. They had finally unlocked the true potential of the carbon nanotubes.

They then spun these purified nanotubes into a continuous thread, nine strands of which were twisted together and wrapped in a flexible insulating polymer to create their “core-sheath composite electric cable.”

The team put the creation to the test and built a motor that ran stably for over an hour. It wasn’t as strong or fast as a copper motor, but it was five times lighter. When the researchers calculated the “specific rotational velocity” — the rotations per minute generated per gram of coil material — the two motors were nearly identical. The carbon nanotube motor was delivering virtually the same performance-for-weight as its copper counterpart. With further development, more powerful yet still light engines could be developed.

Could this be scaled up?

This breakthrough has profound implications. It suggests that we are on the cusp of being able to build electric motors that are significantly lighter without sacrificing efficiency. For an electric car, this could mean a longer range or a smaller, cheaper battery pack. For a drone, it could translate to longer flight times or the ability to carry heavier payloads. In the aerospace industry, where every gram is critical, the potential is enormous.

The problem is scalability.

In this case, there are promising signs. The underlying process used to create the carbon nanotubes is not an exotic, one-off technique. It’s a method that has already been successfully scaled up for the mass production of other industrial materials. Furthermore, the global production of raw carbon nanotubes is already in the thousands of tons per year, suggesting that the base material could be sourced in the quantities needed for commercial production, paving the way for these motors to move from the lab to the factory floor.

As for the authors of the study, they have big plans.

“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,” says Kim.

Journal Reference: Ki-Hyun Ryu et al, Core-sheath composite electric cables with highly conductive self-assembled carbon nanotube wires and flexible macroscale insulating polymers for lightweight, metal-free motors, Advanced Composites and Hybrid Materials (2025). DOI: 10.1007/s42114-025-01302-4