The demands placed on new, high-tech materials are continually increasing, and existing material systems are reaching their limits. Due to their exceptional electrical and mechanical properties, carbon nanotubes (CNTs), graphene and their composite materials offer high potential for use in diverse applications such as photovoltaics, sensors, semiconductor devices, displays, conductors, smart textiles and energy conversion devices (e.g., fuel cells, harvesters and batteries).
Depending on their chemical structure, carbon nanotubes (CNTs) can be used as an alternative to organic or inorganic semiconductors as well as conductors, but the cost is currently the greatest restraint. However, that has the ability to rapidly fall as new, cheaper mass production processes are established.
In electronics, other than electromagnetic shielding, one of the first large applications for CNTs will be conductors. In addition to their high conductance, they can be transparent, flexible and even stretchable. Here, applications are for displays, replacing ITO; touch screens, photovoltaics and display bus bars and beyond.
In addition, interest is high, as CNTs have demonstrated mobilities, which are magnitudes higher than silicon, meaning that fast switching transistors can be fabricated. In addition, CNTs can be solution processed, i.e. printed. In other words, CNTs will be able to provide high performing devices which can ultimately be made in low cost manufacturing processes such as printing, over large areas.
They have application to supercapacitors, which bridge the gap between batteries and capacitors, leveraging the energy density of batteries with the power density of capacitors and transistors.
Challenges are material purity, device fabrication, and the need for other device materials such as suitable dielectrics. However, the opportunity is large, given the high performance, flexibility, transparency and printability.
Companies that IDTechEx surveyed report growth rates as high as 300% over the next five years. New developments regarding the production of pure CNTs and the separation of conducting and semiconducting CNTs as well as applications are given in the newly updated report Carbon Nanotubes and Graphene for Electronics Applications: Technologies, Players & Opportunities.
The situation in Germany
Germany, as well as the rest of the world, is increasingly paying attention to the potential this group of materials offers. More and more start-up companies, networks and projects are dedicating their work to research & development as well as applications of CNTs and Graphene.
Most attention is paid to the field of composite materials of multi-walled CNTs (MWCNT) and their applications, while CNT based electronics are still in its infancy. Conducting composite materials can be used for organic electronics and photovoltaics, especially transparent CNT based electrodes as alternative for ITO.
Over the last few years Germany almost missed the boat on carbon nanotubes and graphene research for electrical and electronic applications. Trying to keep up the Innovation Alliance Carbon Nanotubes (Inno.CNT) was founded in 2008, a research alliance involving around 80 partners from science and industry. Inno.CNT is part of the German government's high-tech strategy and is supported by the German Federal Ministry for Education and Research under its "Materials Innovations for Industry and Society" program.
The initiative comprises 18 coordinated projects. Three of them are involved with crossover technologies and aim to develop solutions for the production, functionalization and dispersion of carbon nanotubes.
Additionally, CONTACT was brought into being, a new research and training project funded by the European Commission's "Marie Curie" programme that involves 10 partner organisations from 7 different countries. The international project is being coordinated by the German Fraunhofer ICT (Institute for Chemical Technology).
The main objective is to carry out research and development on nanomaterials and processes, characterisation methods, simulation tools and of course the implementation of the materials in real world applications including rotor blades for wind power plants and energy storage materials for e-mobility applications.
The research aim of CONTACT is the tailored industrial supply-chain development of CNT-filled polymer composites with improved mechanical and electrical properties. This will involve the optimisation of CNT synthesis and dispersion, and the processing of CNT compounds, as well as the modelling and characterisation of CNT and CNT composites.
The new technologies will be upscaled for applications in four industrial case studies: construction, wind blades, electrically conducting parts and electrodes for redox-flow batteries.
While manufacturers in North America focus more on single-walled CNTs (SWCNTs); Germany, the rest of Europe and Asia, with Japan on top and China second, are leading the production of multi-walled CNTS.
In Germany the main suppliers of carbon nanotubes in large quantities are Bayer Material Science and Future Carbon GmbH. Only recently Bayer MaterialScience (BMS), one of the world's largest polymer companies, invested EUR 22 million into the newly opened pilot facility for the manufacture of CNTs at Chempark Leverkusen. With an annual production capacity of 200 metric tons it is the largest facility of its kind in the world.
BMS is producing and marketing multi-walled carbon nanotubes under the trade name Baytubes®. Bayer MaterialScience (BMS), part of the Bayer Group, is one of the world's leading producers of CNTs - sales of EUR 9.7 billion in 2008.
Leverkusen and the North Rine-Westphalia region gained a leading role in the nanotechnology field worldwide. "We are expecting nanotechnology to create a total of 100,000 new jobs in the German industry in the medium term," said Dr. Joachim Wolff, member of the Bayer MaterialScience Executive segment.
Furthermore, BASF, a world leading chemical company, is joining this field with its expertise. Together with Vorbeck Materials Corp., USA, the company is developing graphene-based dispersions and composite materials, i.e. for the use in printed electronics.
Additionally, several German research institutes and university are increasingly active in the field of CNTs, graphene and their composites.
One of them is the University Stuttgart that is doing research on CNT based thin film transistors (TFTs) suitable for the use in the flexible electronics industry.
Only recently the German Max Planck Institute for Solid State Research in Stuttgart presented their work on coated carbon nanotubes for high-capacity batteries that was done in collaboration with the Beijing National Laboratory for Molecular Sciences in China.
Lithium-ion batteries are in great demand for applications from laptops to hybrid cars - but the list of requirements is long. They need to be lightweight, cheap and environmentally friendly, but also store enormous charge. Coating CNTs with a nanoporous layer of TiO2 results in a crystalline solid made up from 'coaxial cables' that are perfect for trapping lithium ions. When combined, the storage capacity of TiO2 is four times higher than usual and the nanotubes hold three times as many ions. Since the material is simple to produce and far cheaper than electrodes that are based on rare metals, the team is hoping that it can be more widely applied - perhaps for other energy storage devices such as supercapacitors.
Market opportunity for CNTs and Graphene
Worldwide Graphene and MWCNTs are already in fairly high production - tens of tonnes per year. Estimates of the amount of MWCNTs produced in 2008 are about 100 tons in total from companies such as Bayer and Showa Denko. However, most of these uses are for non electronic/electrical products, or simple applications such as electromagnetic shielding.
The commercialization of SWCNTs, relevant to electronics is still in its infancy. The challenge is mainly producing a high yield of SWCNT with a small variation in size in a cost effective, scalable manner. This is the bigger issue rather than processing the materials to make devices, which is nevertheless not insignificant.
While there is capacity in place this year to make tens of tons of SWCNTs, these have a wide range of purity, but for some applications have now reached a tipping point.
For more information on the topic please contact the authors Cathleen Thiele at c.thiele@IDTechEx.com or Raghu Das at r.das@IDTechEx.com.
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