Twisted carbon nanotubes store 3 times more energy than lithium batteries

A collaboration of researchers from Japan and the US has demonstrated how twisted carbon nanotubes can store up to three times more energy than standard lithium-ion batteries. The research could pave the way for new-age implants and sensors that are lightweight, compact, and, more importantly, safe.

Carbon nanotubes are nanometer-sized structures typically made out of a single layer of carbon atoms. Also referred to as graphene, these carbon sheets are extremely light in weight yet stronger than steel itself. The material’s superior properties have helped scientists deploy it for several futuristic applications.

As a researcher at Japan’s Shinshu University, Sanjeev Kumar Ujjain wanted to know if carbon nanotubes could also be used to store energy. In 2022, he moved from Japan to the University of Maryland Baltimore County (UMBC), where he continued his research and found that twisting carbon nanotubes improves their energy storage efficiency.

Inspired by mechanical coil springs

Long before disposable batteries started powering children’s toys, there was the iconic mechanical coil spring. A simple feat of engineering, the spring could be wound up with a key, store the mechanical energy into potential energy, and release it later to facilitate the movement of wheels in a toy.

A scaled-down version of the mechanical coil spring also powered the winding wristwatches of yesteryears, which often displayed the wrong time when the coil was running out of potential energy.

Ujjain was keen to test if the system would work at even smaller scales, and nanoscaled carbon nanotubes were the material of choice for testing his work. His team at the Center for Advanced Sensor Technology (CAST) bundled commercially available carbon nanotubes into ropes and then pulled and twisted them into a single thread, which was further coated with different substances to improve its strength and flexibility.

Measuring performance

To determine how much energy would be released if these ropes were twisted and later unwound, the team conducted several experiments and compared the energy output to multiple materials.

The researchers found that their twisted carbon nanotubes could hold 15,000 times more energy than steel springs per unit mass. While this is commendable, the researchers knew that their biggest competitor was lithium-ion batteries, the highest energy-density device built by humanity.

To their credit, the researchers successfully demonstrated an energy storage density three times higher than the standard lithium-ion battery. Unlike the variable performance that lithium-ion batteries deliver under different operating temperatures, the twisted carbon nanotubes demonstrated consistency in energy storage through a wide temperature range of  -76 Fahrenheit (-60 degrees Celsius) to 212 °F (100 °C).

Since the technology is more mechanical in its approach rather than electrochemical, it is also much safer for devices such as implants. Interesting Engineering has previously reported that scientists are looking for alternate ways to power implants other than batteries.

Ujjain and his team are still far from deploying their technology in an implant anytime soon. The team is working on a prototype sensor to test the twisted carbon nanotubes as an energy source.

“This research shows twisted carbon nanotubes have great potential for mechanical energy storage, and we are excited to share the news with the world,” Ujjain said in a statement .

The research findings were published in the journal Nature Nanotechnology .