Scientists at the Korea Institute of Science and Technology (KIST) have developed a new class of lightweight, highly conductive carbon nanotube (CNT) wiring that does away with copper and aluminum entirely. Using a process called Lyotropic Liquid Crystal-Assisted Surface Texturing (LAST), they've created core-sheath composite electric cables (CSCEC) that don't just conduct electricity, but are flexible and, most importantly, are super lightweight.
Each CSCEC wire was only about 0.3 mm thick, including the insulation. A ~256-μm conductor core with a 10-μm sheath to be specific. That's about a thick as a business card, but still capable of powering a spinning motor.
So far, these CSCECs have been good enough to replace all the copper in a small electric CNT-based motor powering a model car.
"By developing a new concept of CNT high-quality 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 trick was the LAST process. Using lyotropic liquid crystals – a phase of matter that flows like a liquid but still has some directional order like a crystal – helps align and separate otherwise clumped together individual carbon nanotubes. Combined with a chemical rinse, the process also removes metal catalyst impurities created during manufacturing while maintaining the critical one-dimensional nanostructure that makes CNTs so special.
The LAST procedure boosts conductivity by over 130%, drops a ton of weight, and keeps the performance of the CSCECs stable over time.
When it comes to efficiency, battery life, range, and every other metric to go further, faster, higher, etc, weight matters.
Traditional electric motors, while generally significantly lighter than their ICE counterparts, are still relatively heavy. A fair amount of that weight can be attributed to the copper windings in the stators – not to mention all the associated copper wiring in a vehicle's harnesses.
KIST's recent developments speak to electric motors specifically, but one would hope this technology might be applied to general electrical wiring as well.
Take BEV (battery electric vehicle) cars for example: A dual-motor Tesla Model S front motor weighs about 70 lb (31.8 kg), while the rear is about 80 lb (36.3 kg). About 25% of that motor weight is copper windings. If replaced with CSCEC wiring, it could bring the overall weight of the front and rear motor down from 150 lb (68 kg) to ~115 lb (52.2 kg).
It might not seem like a huge amount on a car that already weighs 4,561 lb (2,069 kg), but you also have to take into account the lower inertia. Less rotating mass means potentially a faster spin-up, better throttle response, more efficient torque delivery and lower mechanical losses. Thermal load would also be lower, so now the cooling system can be made smaller and lighter. It's a cascading effect that only leads to better battery life and longer range.
That's all just hypothetical based on actual Tesla figures, however, KIST tested its electric motor between 2 and 3 volts at 3.5 watts – significantly lower power figures than any real-world electric vehicle bigger than a children's toy.
But since I'm on a hypothetical tangent, let's go even further for a second: While there's no public data on Joby's actual copper content, I'd take an educated guess and say that it has 200-300 lb (91-136 kg) of wiring harness for all its redundant systems. It has six motors, each with likely around 30-40 lb (13.6-18.1 kg) of copper windings, totaling 180-240 lb (81.6-108.9 kg) in all.
Again, KIST has only talked about electric motor windings at low voltage, but if researchers were able to solve high-voltage and general wiring with CSCEC, we're talking about shaving 300-500 lb (136-227 kg) from the number one air taxi in the world. I bet if you asked any Joby engineer if they'd like to shed a quarter ton from their eVTOL, they'd probably just stare at you in shock before readily agreeing.
Back to the real world, there are a few other catches and caveats in the research so far.
Even after the LAST process, CNT wiring can't match copper's raw electrical conductivity (~7.7 megasiemens per meter vs copper's 59 MS/m). For the same physical dimensions and voltage, less current flows through CNT wire, resulting in lower output. In the KIST study, for example, the CNT-based motor topped out at 3,420 RPM, while the copper equivalent hit 18,120 RPM.
But, the CNT motor's conductor core weighed one-fifth that of the copper one. That means its specific rotational velocity – a useful aerospace metric, where weight generally matters more than force – was about 6% lower than copper's. So, performance per unit weight isn't terribly far behind copper in that respect.
Then there's cost. Specialized carbon nanotube core-sheath composite electric cables can cost upwards of US$$375-500 per kg to manufacture vs copper's comparatively tiny $10-11 per kg.
And it's not as though you'd be able to simply swap out copper for CNT tech on existing products. Engineers would have to redesign everything from the ground up to accommodate new types of insulation and winding geometry.
Researchers have said that more fine-tuning – like optimizing polymer sheaths or aligning CNTs better – could boost conductivity, closing the gap with copper even more.
While CNTs can reduce material mass significantly, the manufacturing of them doesn't come without a hefty environmental price tag – most are still made from fossil fuels in energy-hungry processes that generate toxic byproducts we still have to contend with. For example, the LAST process uses chlorosulfonic acid and creates hydrochloric acid in the rinse stage.
But is strip mining for copper any better?
Source: Springer Nature Link
