Carbon nanotubes, a tubular structure formed by curling highly graphitized carbon atoms, has been put forward in the 1950 s and found and applied for a patent in the coking materials of ethylene cracking furnaces in the 1970 s, however, its atomic structure was not clearly revealed and defined by high-resolution electron microscope technology until 1991. Scientists have thus realized that it has ultra-high strength, toughness and excellent electrical and optical properties, thus becoming a research hotspot in academia. In the past 30 years, the international community has conducted comprehensive research and research on the intrinsic structure, physical and chemical properties, control, macro preparation and commercial application of carbon nanotubes. It not only makes its macroscopic mechanical strength more than ten times of the best carbon fiber known at present, but also manufactures and exhibits 16-bit computer chips of all-carbon nanotubes, small and fast switching speed X-ray tubes, etc. The industrialization progress of carbon nanotubes has also developed rapidly. Tiannai science and technology company has realized the capacity of multi-walled carbon nanotubes in a 1000-ton fluidized bed method. ZEON company, OCSiAL and northern Guoneng and other companies have achieved the capacity of ton-level single-walled carbon nanotubes. Recently, LG company also announced a 1700-ton/year multi-walled carbon nanotube production line. The application of carbon nanotubes has made great progress in many aspects from conductive polymer materials, battery materials, super-strong materials to the industrialization of electronic chip materials. Obviously, the development process of carbon nanotubes is the crystallization of a typical interaction between industry and academia. According to incomplete statistics, there are more than 100 carbon nanotube manufacturing enterprises worldwide, with a production capacity of over 10,000 tons/year. This makes us see the spring of industrialization development of carbon nanotubes in the unusual spring of 2020.
1. Fluidized bed-chemical vapor deposition technology has become the mainstream macro preparation technology, providing material basis for commercial application.
Through more than 30 years of in-depth research, people have realized that template self-catalysis with hydrocarbons and transition metals as the core is an efficient method to grow carbon nanotubes, and its large-scale preparation depends on the progress of Chemical Technology. Taking hydrocarbons as raw materials and adopting gas-solid fluidized bed reactor technology and engineering amplification method with excellent heat and mass transfer performance, Tsinghua University realized the batch preparation of carbon nanotubes 20 years ago. With the progress of batch preparation technology, the price of multi-walled carbon nanotubes has been lower than that of some high-end activated carbon from 60 usd/g 20 years ago, and its cost has decreased by nearly three orders of magnitude, successfully integrated with the market. High quality and low price carbon nanotubes provide material basis for various performance research and significantly promote the commercial application process. However, the demand of macro application market plays a significant role in boosting the production scale of a single production line exceeding 1000 tons per year.
2. The development of new electrochemical energy at home and abroad provides a stage for the commercial application of carbon nanotubes.
The high conductivity, small diameter and large diameter ratio of carbon nanotubes are extremely suitable for building a light and excellent conductive network without hindering ion transmission. With this excellent performance, carbon nanotubes, as the conductive agent of lithium ion battery materials, have been filled and applied at the beginning of the birth of lithium ion batteries. In recent years, it has gradually replaced traditional conductive agents such as conductive carbon black and nano carbon fiber, and has been widely used by lithium ion battery enterprises. Due to the huge aspect ratio of carbon nanotubes, they can obtain excellent performance at a very small amount of filling, thus not only reducing the internal resistance of the battery, but also improving the cycle life of the battery, moreover, more positive electrode materials can be added to indirectly improve the energy density of the battery.
It is worth pointing out that since 2007, lithium ion battery, as the representative of new electrochemical energy, can be used not only for batteries of mobile electronic devices such as mobile phones and computers, it is also used as the main power supply of pure electric vehicles and the start-stop power supply of hybrid electric vehicles. These important and huge application fields such as communication and transportation are the main markets of new electrochemical energy storage equipment at home and abroad, and have become the national strategies of many countries. At the same time, many countries have put forward the ban schedule of traditional fuel vehicles one after another, which has also promoted the application of carbon nanotubes in the field of power batteries and occupied an important market share.
Specifically, the market demand for long-distance cruising of new energy vehicles poses a great challenge to the energy density of power lithium ion batteries, at present, the technology route with the most industrial competitive advantage is "high nickel ternary positive pole + silicon-based negative pole". Carbon nanotube conductive agent will play an irreplaceable role in improving the conductivity of high nickel ternary positive electrode and silicon-based negative electrode materials, and will further accelerate the market replacement of other traditional conductive agents. According to statistics, the output of ternary power lithium ion battery in 2018 increased by 118% year-on-year to 41.6GWh. In the ternary power lithium ion battery, carbon nanotube conductive paste is mainly used, which increases the market scale of carbon nanotube conductive paste by 30.1% year-on-year. It is estimated that by 2023, the market output value of carbon nanotube conductive paste for global power lithium ion batteries will exceed 2.4 billion yuan, and the compound annual growth rate in five years will reach 40.3%. The growth mainly comes from the Chinese market, as well as the acceleration of the import of carbon nanotube conductive paste by Japanese and Korean enterprises. From the prediction of technology development roadmap, the market scale of power lithium ion batteries will still maintain a high-speed growth trend in the next few years and will continue to drive the market application of carbon nanotubes.
In addition, grid-side Energy storage has become an important development strategy for the United States, China, Australia and other countries. Lithium ion batteries are still the energy storage system with the largest installed capacity. The annual installed capacity of lithium ion battery energy storage systems in the United States and China exceeds GW level. However, in this large energy storage system (single system exceeds MW level), more attention is paid to safety and long service life. Carbon nanotube conductive agent can effectively reduce the internal resistance and calorific value of the battery, and has more advantages than other conductive agents. This will also further stimulate the blowout of the carbon nanotube market.
3. The field of composite materials is the key to expand the application market of carbon nanotubes and has great potential.
(1) conductive plastic field
As anti-static and electromagnetic shielding materials, conductive plastics have become hot materials for research and development at home and abroad, and the application of Electrostatic protection and electromagnetic radiation protection materials is gradually increasing. Carbon-filled conductive plastic has formed industrial production and mature market by virtue of its advantages of high cost performance and adjustable resistance. International mainstream manufacturers of carbon-series filled conductive plastics are concentrated in the United States, Europe and other places. There is still a big gap between China's related products and foreign products in terms of variety and quality stability. The degree of localization is low in terms of semi-conductive layer shielding materials of high cables and products related to integrated circuits.
In the application of filled conductive plastics, carbon nanotubes have obvious advantages in conductivity and mechanical properties than traditional fillers such as carbon black, and their application proportion has been gradually improved in recent years. With the expansion of the preparation scale and cost reduction of carbon nanotubes, as well as the gradual maturity of carbon nanotube dispersion technology, the technical barriers have been broken through, which will have a significant benefit on the application of carbon nanotubes in the field of conductive plastics.
(2) the field of metal matrix composites
Metal materials are the most widely used structural strength materials and have a wide range of applications. However, traditional metal materials have low specific strength and cannot effectively meet the needs of ultra-light quantification, super-strong and super-tough applications. However, carbon nanotubes have huge aspect ratio and excellent mechanical, electrical, optical and thermal properties. Using carbon nanotubes as reinforcements to build metal matrix composites has the advantages of light weight, high strength and toughness, corrosion resistance and high temperature resistance, and has become a hot spot in the field of new materials such as aerospace, national defense and automobiles.
4. The new field of 5G and the new battlefield of high-end carbon nanotubes will be the commanding height of international high-end technology competition in the future.
(1) in the field of chip manufacturing, technical breakthroughs have been made in the application of high-end carbon nanotubes as substrates.
Nanometer access storage (NRAM), as a new type of non-volatile memory based on carbon nanotubes for information storage. It mainly uses the excellent and separated electrical conductivity of carbon nanotubes to replace the field emission transistor (FET) based on traditional semiconductor materials, and according to the identification of carbon nanotube arrays, two kinds of resistance states (0 or 1) under different micro acting forces (electrostatic or Van der Waals adsorption) to achieve the function of storing data.
The excellent mechanical and electrical properties of carbon nanotubes make NRAM have strong durability and thermal stability, as well as high speed and low power consumption. Specifically, NRAM has the following performance advantages: first, because carbon nanotubes have excellent chemical stability, it can ensure that NRAM can be in extreme environments such as high temperature, extreme cold, radiation and vibration, works properly. The service boundary of the memory is effectively expanded and its service life is significantly improved. Secondly, on the premise that the reading speed is as fast as DRAM (I .e. dynamic random access memory, the most common system memory at present), the power consumption of NRAM is lower, and the power consumption in standby mode is basically zero. Moreover, the excellent mechanical properties of carbon nanotubes make NRAM carbon nanotube electromechanical switches have good repeatability and are expected to have unlimited (more than 1011 times) access endurance. Finally, the manufacture of NRAM only needs a layer of carbon nanotube coating (for data storage), which is much simpler than the preparation process of traditional memory multilayer coating, so the cost is low.
(2) in the field of flexible electronic devices, carbon nanotubes have moved towards industrialization.
For more "high-end" applications such as electronic devices and sensors, higher requirements are put forward for the purity, orderliness, density, conductive properties and even chirality of carbon nanotubes. For example, IBM sets that the purity standard of semiconductor single-walled carbon nanotubes for transistors is higher than 99.9999%, and the density should reach 125/μm.
Carbon nanotube flexible electronic devices have better performance than traditional transparent thin film semiconductors. For example, based on the transparent conductive film of super-row carbon nanotube array developed by tsinghua-foxconn nanotechnology research center, the industrialization of mobile phone touch screen has been realized through tianjin funa yuanchuang technology co., ltd, and successfully matched huawei, coolpad, ZTE and other mobile phones. Canatu company of Finland, taking advantage of the technology of Kauppinen research group of Aalto University, is promoting the application of 3D Touch screen with single-walled carbon nanotubes that can be stretched and deformed.
5. Safety of carbon nanotubes, relevant international and national standards and intellectual property protection
(1) safety of carbon nanotubes
As a new artificial material with very small diameter, carbon nanotubes are used in powder or composite states, and their related safety (such as skin absorption or respiratory inhalation) is an important issue. However, due to many kinds of carbon nanotubes, large differences in diameter, length and chemical stability, and different dispersion states, scientists have different conclusions on toxicity analysis of carbon nanotubes at present, A comprehensive conclusion has not been given yet. In general, the materials in the powder state need to pay more attention to protection. It is necessary to standardize management and establish relevant systems to reduce the contact between practitioners and carbon nanotube powder in the production process. For example, Bayer company of Germany proposed that the upper limit of occupational exposure of carbon nanotubes was 50mg/m3. According to the results of animal experiments, the National Institute of Occupational Safety and Health recommends that the occupational contact limit of carbon nanotubes is 7 μg/m3. In addition, the chemical stability of carbon nanotubes has also become the focus of environmental degradation research. Scientists are carrying out research on the whole life cycle analysis of carbon nanotubes, which is expected to demonstrate the impact of carbon nanotubes on human society from a larger time and space scale and prevent the negative effects of new materials on human life. In general, the chemical degradability of carbon nanotubes should be better than graphite and carbon fiber materials, and relevant management regulations can be used for reference.
(2) International and national standards related to carbon nanotubes
With the continuous advancement of carbon nanotubes in commercial application, international and national standards related to carbon nanotubes have been formulated and issued one after another.
Among them, the national standard of "multi-walled carbon nanotubes" issued by China in 2009 and implemented in 2010 (GB/T 24491-2009) and the national standard (GB/T 24490-2009) of "detection method for purity of multi-walled carbon nanotubes", which stipulates the terms and definitions, classification, technical requirements, test methods, inspection rules, packaging, marks and quality certificates, storage and transportation, safety precautions, etc., and purity methods, instruments, analysis steps and result representation methods.
The national standard (GB/T 33818-2017) of carbon nanotube conductive paste published and implemented in 2017 stipulates the terms, requirements and detection methods, detection rules and marks of carbon nanotube conductive paste, packaging, transportation, storage and order content. It is suitable for quality inspection and acceptance of liquid phase series products using multi-walled carbon nanotubes as conductive medium in the fields of lithium ion batteries, conductive coatings and conductive adhesives.
Implemented in 2020, the international standard of carbon nanotube conductive paste (ISO/TS 19808) led by tenet technology as the representative of China, the characteristics of multi-walled carbon nanotube slurry and the corresponding measurement methods are described.
These standardization efforts will contribute to the development of independent commercialization, compatibility, interoperability, safety and regeneration of carbon nanotubes.
(3) intellectual property protection of carbon nanotube industry
The accelerated process of industrial application of carbon nanotubes makes the protection of intellectual property rights in this field more and more important. In fact, because Hyperion company's patent layout in the field of conductive plastics in advance hinders the research and development of large international companies in many fields, carbon nanotubes in a long time, it is only applied in a few occasions such as camera sleeves. In recent years, companies that have applied for more patents in the field of carbon nanotubes are concentrated in Japan, South Korea and China. The further expansion of the market in this field will drive the continuous evolution of the patent pattern of the company as the patent holder, and become the driving force for the change of this emerging material and nanotechnology. Paying attention to the protection of intellectual property rights in this field will help the benign and healthy development of new industries.
In short, carbon nanotubes are gradually commercialized in these fields and will occupy the market advantage of online iteration in competition with other materials. Carbon Black, as the earliest and widely used carbon material, has a usage history of more than 2,000 years and has reached the usage of 10 million tons/year. It is estimated that in the next 30 years, the market share of carbon nanotubes in lithium ion batteries will continue to increase, reaching 100,000 tons/year usage. However, the application of high strength, high conductivity and antistatic shielding materials may stimulate the production capacity of millions of tons and the actual composite material application market of tens of millions of tons. It will have a wide range of influence in the fields of super-strong materials, functional composite materials, chips and optoelectronic materials, etc,
