Carbon nanotube-based cables carry four times the current of copper

Carbon nanotube-based fibres invented at Rice University have greater capacity to carry electrical current than copper cables of the same mass, according to new research.

While individual nanotubes are capable of transmitting nearly 1,000 times more current than copper, the same tubes coalesced into a fibre using other technologies fail long before reaching that capacity.

However, a series of tests at Rice showed that wet-spun carbon nanotube fibre out performed copper, carrying up to four times as much current as a copper wire of the same mass.

That, the researchers claim, makes nanotube-based cables an ideal platform for lightweight power transmission in systems where weight is a significant factor, such as in aerospace applications.

The analysis led by Rice professors Junichiro Kono and Matteo Pasquali have appeared in Advanced Functional Materials.

Present-day transmission cables made of copper or aluminium are heavy because their low tensile strength requires steel-core reinforcement.

The ideal cable would be made of long metallic ‘armchair’ nanotubes that would transmit current over great distances with negligible loss, but such a cable is not feasible because it’s not yet possible to manufacture pure ‘armchairs’ in bulk, Pasquali said in a statement.

Pasquali’s lab has created a method to spin fibre from a mix of nanotube types that still outperforms copper. The 20 microns wide cable developed by Pasquali and Netherlands-based companyTeijin Aramid is strong and flexible also.

Pasquali asked Kono and his colleagues, including lead author Xuan Wang, a postdoctoral researcher at Rice, to quantify the fibre’s capabilities.

The researchers analysed the fibre’s current carrying capacity (CCC), or ampacity, with a custom rig that allowed them to test it alongside metal cables of the same diameter. The cables were tested while they were suspended in the open air, in a vacuum and in nitrogen or argon environments.

Electric cables heat up because of resistance. When the current load exceeds the cable’s safe capacity, they get too hot and break. The researchers found nanotube fibres exposed to nitrogen performed best, followed by argon and open air, all of which were able to cool through convection. The same nanotube fibres in a vacuum could only cool by radiation and had the lowest CCC.

‘The outcome is that these fibres have the highest CCC ever reported for any carbon-based fibres,’ Kono said. ‘Copper still has better resistivity by an order of magnitude, but we have the advantage that carbon fibre is light. So if you divide the CCC by the mass, we win.’

Kono plans to further investigate and explore the fibre’s multifunctional aspects, including flexible optoelectronic device applications.

Pasquali suggested the thread-like fibres are light enough to deliver power to aerial vehicles. ‘Suppose you want to power an unmanned aerial vehicle from the ground,’ he said. ‘You could make it like a kite, with power supplied by our fibres. I wish Ben Franklin were here to see that.’