On the history and future of carbon nanotubes


Before there were carbon nanotubes, there was Morinobu Endo. Like the semiconductor industry itself, Endo has been battling manufacturing problems for more than 30 years. Call it Endo’s Law: his process for manufacturing carbon nanotubes has been increasing its yield by a factor of 10 every year for the past 15 years.

How has he done it? Hard work, innovation, serendipity...and inspiration from a sneeze. Endo, a professor at Shinshu University in Nagano, Japan, recently shared his perspective on carbon nanotubes, their development and their future applications in an interview with Small Times’ David Forman.

Q: When did commercial activity begin?

We have been working on carbon since 1970, and we had been working already on other kinds of the nanotube materials. We started commercialization after scientific results based on my research. We started by cooperating with a chemical company in Japan for the industrialization of multiwall carbon nanotubes in 1988.

There were a lot of breakthroughs we made. For example, in my carbon nanotube production the past 15 years, we increased 10 to 15 times the production each year. It does not correspond to a scale up of the plant. The (increase in productivity) is from (technical) breakthroughs.

Q: So it’s not only scale up but also innovation?

Innovation, yes. The 10-times increase every year corresponds to some innovation of production.

Q: In process?

In the process. But not only process, also the quality control. Because you know for industrialization - commercialization of materials - we need not only the scientific result but also we need the industrial breakthroughs because we must guarantee the product for the user.

We (need) a very high level of reliability of the product materials. That corresponds to quality control. So the quality is also a very big part of the control.

Q: One of the things I am curious about in the history is that one of the first papers on carbon nanotubes was considered to have been published in 1991. But you had been working with these materials before. What did you call carbon nanotubes prior to 1991?

I said they are ultrathin carbon fiber with hollow structure, with hollow tube structure.

Q: But it is the same?

It is just the same as the carbon nanotube. In a paper in 1976 I proposed already the growth model at the tip of that kind of hollow tube. We find already the hollow core. This is carbon nanotube already....And already under some broken part the central core extrudes.

At the tip of the tube...I found (that) there is iron (and) the iron grows. The small ultrafine iron grows the tube.

Q: As the leading edge?

The leading edge, yes. So this is the growth mechanism I explained.

After 10 years they asked me to give another paper. We did continuously that work since 1976 and my first paper. At that time, I thought this was very curious. This iron particle, where does it come from? We used sandpaper on the substrate. Sand paper consists of iron oxide. At that time I didn’t know but I unintentionally used this paper. Innovation is very, very curious. One time we used black paper and there are no tubes, no growth.

Q: So you determined that the sandpaper is where the iron is coming from?

Yes, because of the iron oxide. And I constructed this model people now use a lot by using the iron catalysts for chemical vapor deposition growth. At that point I intentionally dispersed the iron particle. In this case, the iron oxide is intentional. Controllability is important for nanotechnology.

I found that the smaller diameter of a catalytic particle gives a higher yield of the materials. So I already find small particles of iron can grow more tubular materials. This I called (the) substrate seeding method. (It is designed) intentionally so I can get a lot of tube.

(The breakthrough came) when I went to a public meeting in Tokyo. This meeting is always in November. In those days the general newspaper wrote about a very bad situation for influenza. It made me think. When people have a cold - and sneeze - it can float about 15 meters.

Oh, (I said), my particle is much smaller than the influenza virus so I can float that catalytic particle and perhaps if I am lucky I’ll get the tube there.

Q: So you were inspired by the sneeze?

Yes. So as soon as I got back from Tokyo I tried to float the catalytic particle like that and I get the same materials. So it was a very strong breakthrough. One week we have the catalytic particle on the substrate. But the cost of the material is about $2,000 per kilogram. Too expensive compared to conventional materials. The next week we have a very big breakthrough because the reproducibility is a thousand times improved because we can provide the catalytic particle continuously.

Q: So what were the first applications?

That is a very important question. I contacted at that time NASA people and aerospace company people and high tech companies in the United States. And they say, “Endo, very beautiful material. Very nice. But even in space we should evaluate the cost of the method.” And so I decided already at that time that since the price of carbon fiber degrades year-by-year that we can’t compete with carbon fiber. I wanted to develop an application field for this material where it is only possible to use our material - hollow tube, carbon nanotube...Endotube, people say.

Q: An application where you must use this material?

Yes, no substitutions. Because if we did substitution perhaps the counterpart would degrade the price.

Fortunately at that time, in 1988, there were very important breakthroughs for electronics. Do you remember? In the 1990s electronics like laptop computers...they were not so good. Basically all electronics used a power line, a power source. The battery was only the auxiliary system.

At that age personal computers changed from the black and white display to color display and Intel starts the high power CPU. So the laptop computer needs more high power. And also the people start the cell phone but they use a very big battery box. And also people use the video camera but people used a very big battery box.

So there is a lot of demand to develop a good battery, a high quality battery. The requirements of energy consumption were increasing for this laptop computer. So the companies were very aggressive in Japan to develop a new battery, the lithium-ion battery. Some companies used our multiwall carbon nanotubes.

Q: And how did they use your materials?

It’s very top secret. I can’t say that part. But anyway the lithium-ion battery starts in 1991 and year by year it increases. In 1991 the worldwide battery production is only 10 million batteries. Last year about 1,000 million sold.

Q: Do all of those batteries use the material?

You know, it’s very expensive with our multiwall tube. It is for the very high quality battery. For very thin (batteries) or very high power it is necessary.

This lithium ion battery provides the era of wireless computing - cordless, portable electronics. If not, we would have the big telephones. So energy storage is very important. And also for the future, for motor vehicle technology. The ideal case could be the electric car, not the fuel cell. Even for fuel cell cars, even for hybrid vehicles, energy storage technology is key. If we use electricity generated by the wind, atomic, coal, whatever, we can get the highest efficiency of a car. Because power plant efficiencies are 42 percent in this country. For gasoline car, it is only 10 percent of the efficiency. Hybrid car is only 20 percent. But if we use electricity generated by power plant we can get twice the efficiency. For that kind of battery this type of material is very important.

Also it is (important) for power tools. Carpenters use very high grade and long-life electronic tools. The lithium-ion battery is very nice for electronics. It’s not powerful like lead-acid battery but recently they have improved very much the performance. The performance must still increase. When the performance increases you can expand the application field. This is very important.

Q: What about the ability to quickly recharge?

That is a good question. So I should say the performance of the lithium-ion battery can improve a lot by putting this multiwall carbon nanotube in the electrode. This is a mechanism. Nanotubes are not the main material but a very important, I should say, an essential additive to get high repeatability and cycle-ability.

Batteries are now a strategic technology because the battery company connects with the cell phone company. The battery company connects with the laptop computer company. And these companies every two years they want to have some special laptop computer. They want to sell some special cell phone. We can know what kind of cell phone will be possible from the battery size and capacity that exists. So that’s very strategic. The battery now is a very strategic component.

The Endo file

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Morinobu Endo is a professor in the faculty of engineering at Shinshu University in Nagano, Japan. His current work ranges from basic science to applications of various forms of carbon, carbon nanotubes, new forms of carbon and graphite, nano-porous carbons, graphite intercalation compounds, Li-ion batteries and electric double layer capacitors.

After receiving an M.S. degree from Shinshu University, Endo obtained a Ph.D. from Nagoya University. He is the present chairman of Japan Carbon Society and is one of the international advisory members of CARBON journal. His work developing carbon nanotube processes, specifically a 1976 paper in Journal of Crystal Growth and a 1988 paper in CHEMTECH, the former journal of the American Chemical Society, is considered fundamental.