COMMENTARY | FOCUS
The global growth of graphene Wencai Ren and Hui-Ming Cheng The large-scale production of graphene aimed at industrial applications has grown significantly in the past few years, especially since many companies in China have entered the market.
G
raphene is the thinnest imaginable material and is highly transparent; it is the strongest material ever examined, the most stretchable crystal, the most impermeable material, even to helium; it has a record thermal conductivity 10 times as high as copper, and the highest intrinsic electron mobility, about 100 times that of silicon1. Graphene has been discussed theoretically since the 1940s2, but it took 60 years to experimentally obtain a few sheets of micrometre-sized high-quality flakes weighing picograms3. Yet, only 10 years since Geim and Novoselov first used adhesive tape to isolate graphene from graphite, graphene sheets are being produced in hundreds of tonnes and tens of thousands of square metres. Five years ago, only a few USAbased small start-up companies, such as Angstron Materials, Vorbeck Materials and XG Sciences, were making large volumes of small graphene sheets4. Since then, tens of graphene manufacturing companies have sprung up all over the world, which produce not only small graphene sheets but also large-area, high-quality graphene films on an industrial scale. In particular, the production industry of graphene materials in China has been developing very rapidly, and its total annual production capacity of small graphene sheets and graphene films exceeds 400 tonnes and 110,000 m2, respectively.
Mass production methods of graphene
Small sheets and large-area films are two major forms of graphene used for various applications. Small graphene sheets can be used in composites, functional coatings, conductive inks, batteries and supercapacitors5,6. Large-area graphene films can be used as transparent electrodes in touch panels, displays and photovoltaic devices with potentially low cost, and more importantly, they are expected to be used in next-generation electronics and optoelectronics such as flexible and wearable devices6,7. Exfoliation of bulk graphite (the topdown approach) is the most commonly used method for the mass production of small 726
graphene sheets. This can be through direct exfoliation in a liquid, with or without the use of a surfactant 8, or in the solid state by edge functionalization9, or by first inserting a chemical species between the graphene layers in graphite to weaken their interaction followed by exfoliation10–12 (Fig. 1a). Bottomup approaches such as substrate-free chemical vapour deposition (CVD) and solvothermal and combustion processes have also been developed. Depending on the strategy used, there are considerable differences in yield, efficiency, cost, accompanying pollution, ease of production and scalability of the manufacturing process, and in the morphology, structure and properties of the products such as thickness, lateral size, surface chemistry, solubility, defect and impurity contents, and electrical and thermal conductivities (Fig. 1 and Table 1). To produce uniform monolayer and few-layer graphene sheets with high yield and high efficiency is a universal challenge for all these mass production methods. Chemical assembly of small graphene sheets and CVD are two methods to produce large-area graphene films5,7,13–19 (Fig. 1b and Table 1). Chemical assembly can be easily realized on various substrates at low temperatures, but the films obtained suffer from poor quality, for example low electrical conductivity 5,7,13. CVD produces high-quality graphene films by the catalytic decomposition of hydrocarbons on a metal (for example, Cu, Ni, Pt or alloy) surface at high temperatures, and the films are then transferred to transparent substrates such as glass and polymers by etching away the metal or by non-destructive electrochemical bubbling for transparent conductive film (TCF) applications14–19. Roll-to-roll (R2R) CVD growth and transfer techniques have been developed to fabricate large-area TCFs16,17. Films produced over a large area, however, usually show performance inferior to high-end indium tin oxide films but with higher cost. How to realize direct growth of large-area uniform defect-free few-layer graphene films on arbitrary substrates, and how to transfer the films intact and cleanly
from a metal substrate without sacrificing it, so that it can be re-used, are two big challenges for the CVD production of highperformance, low-cost graphene TCFs.
Industrial production of small sheets
Exfoliation of graphite is the most widely used method for the industrial production of small graphene sheets (Table 1). Angstron Materials in the United States and Thomas Swan in the United Kingdom are two representative manufacturers that use direct liquid-exfoliation methods to produce high-quality pristine graphene materials. Thomas Swan’s first integrated process producing kilogram quantities per day will be up and running by September 201420. Although this process is easy to realize and scale up (graphene materials can even be produced using a kitchen blender 8), it produces a mixture of small-size monolayer or few-layer graphene sheets and even thin graphite flakes, and suffers from surfactant or organic solvent contamination. China’s graphene manufacturers mostly use oxidation–exfoliation–reduction10,11 and intercalation–exfoliation12 methods to produce small graphene sheets. The Sixth Element (Changzhou) Materials and Tianjin Plannano Technology use oxidation to form oxygen-containing functional groups covalently bonded with the graphene layer to weaken the interlayer interaction of graphite. Oxidation makes a dispersion of graphite oxide difficult to handle and to clean, resulting in low efficiency; it also leads to severe structural damage to the graphene layer and produces a lot of pollution. But the exfoliation of purified graphite oxide in water by stirring and sonication produces a water-soluble functional material, graphene oxide, which is easy to use for many applications. The graphene oxide is usually very thin and can be reduced to graphene, and defects and residual functional groups in the reduced graphene oxide are beneficial for applications such as catalysis, mechanically enhanced composites, and composite electrodes in batteries and supercapacitors. Sixth Element set up a mass production line with a capacity of
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FOCUS | COMMENTARY a
• Liquid exfoliation Pristine graphene sheets
Sonication, shearing, ball milling
Raw material: graphite
NMP, GBL, DMEU, DMF, IPA H2O + (sodium cholate, SDS, SDBS, PVA) • Solid exfoliation Nearly pristine graphene sheets
Edge-functionalized graphene Ball milling
Thermal annealing
Dry ice, oxalic acid
Ar, N2
• Oxidation–exfoliation–reduction Graphite oxide (Modified) Hummers, Brodie, Staudenmaier
Sonication, Graphene oxide, stirring functionalized graphene H2O, NMP, DMF, ethanol, THF, PC Rapid heating, microwave, arc discharge Ar, H2, air
NaNO3, KMnO4, H2SO4, KClO3, HNO3
Thermal annealing Ar and/or H2, vacuum Hydrothermal
Reduced graphene oxide
Chemical reaction Hydrazine, NaBH4, hydrazine hydrate, alcohols NaOH, KOH, VC, HI
• Intercalation–exfoliation Heating, stirring, electrochemical
Intercalated graphite
Sonication
Chemical reaction H2O, ethanol, H2O2, TBA
K, Cs, NaK2, K/THF, ClF3, ICl, IBr, FeCl3, Li/PC, H2SO4, eutectic salt, CSA, H2O2, ionic liquids
b
Small graphene sheets
Solid exfoliation Easy to realize Agglomeration, non-uniformity
H2O + SDBS, sodium cholate (aq.), ethanol, NMP, pyridine, DMF, CSA, DSPE-mPEG
Large-area graphene films Substrate CVD Large area Difficulty in growing large-area uniform quality multilayers on arbitrary substrates, and intact transfer from metals
Liquid exfoliation Intercalation–exfoliation Easy to realize High yield Low yield, small size, Usually thick, low concentration, non-uniformity non-uniformity, impurities
Quality
Pristine graphene sheets
Expanded graphite
Heating, microwave
Substrate-free CVD High purity Low yield, low efficiency, small size Assembly Low temperature, easy to realize, applicable for various substrates Low conductivity
Chemical reaction Oxidation– Small size, exfoliation–reduction low purity Easy to functionalize, processable Low efficiency, serious pollution
Cost
Figure 1 | Main mass production methods of graphene. a, Four typical methods for the mass production of small graphene sheets by exfoliation of bulk graphite. b, Comparison of the quality and cost of graphene products manufactured by different methods. NATURE NANOTECHNOLOGY | VOL 9 | OCTOBER 2014 | www.nature.com/naturenanotechnology
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COMMENTARY | FOCUS Table 1 | Basic synthesis method, product, production capacity and main application products of several big graphene manufacturers. Graphene Basic synthesis manufacturer method
Basic product
Production capacity
Main application products
Angstron Materials (USA)
Liquid exfoliation
Pristine nanographene platelets Thickness: 90%, 200–400 Ω per square at >85% transmittance (including substrate)
30,000 m2 (May 2013) 200,000 m2 (December 2014)
Touch panels
Wuxi CVD Graphene Film (China)
Graphene films on Cu, PET Film on PET: ~600 Ω per square at >97% transmittance (excluding substrate)
80,000 m2 (December 2013)
Touch panels, touch sensors (5 million pieces, December 2013)
PowerBooster (China)
Graphene films on Cu, PET Film on Cu: available maximum size 7.5 m2 (2013) Film on PET: 50–140 Ω per square at 95.5% transmittance
-
Touch panels
CVD
100 tonnes per year in 2013. The USA-based Vorbeck Materials uses similar technology to produce functionalized graphene with a unique wrinkled morphology 11. Ningbo Morsh Technology, Deyang Carbonene Technology and XG Sciences are using non-oxidation intercalation 728
to produce high-quality pristine graphene materials, which are suitable for applications requiring high electrical and thermal conductivity. This process is easier to scale up and more efficient, causes less pollution than the oxidation route and has a much higher yield than the
direct liquid-exfoliation route. However, the product is usually thick. XG Sciences reached an annual production capacity of 80 tonnes in 2012, and its product has an average thickness of ~2 to 15 nm. In 2013, Ningbo Morsh opened a production line with an annual output of 300 tonnes
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FOCUS | COMMENTARY a
b
c
d
100 nm
1 nm
Figure 2 | Mass production and application of small graphene sheets. a, A shipment of few-layer graphene product manufactured by Deyang Carbonene Technology. b, Graphene-coated aluminium current collectors for lithium ion batteries. c,d, Transmission electron micrograph (c) and aberration-corrected high-resolution transmission electron micrograph (d) of the product in a, showing its very high quality. Images: a, © Deyang Carbonene Technology; b, courtesy of Songfeng Pei; c,d, courtesy of Zhibo Liu.
impermeability, small graphene sheets have also been explored as antistatic and anticorrosion coatings. Developing thermal interfacial or heat-spreading materials that make use of graphene’s high thermal conductivity in electronics such as in mobile phones and light-emitting diodes is another application focus in China. a
The United States and Korea pioneered research on the CVD growth of graphene films14–16. Together with China and Japan, they are devoted to the industrial production of graphene films in this way. Bluestone Global Tech is a USA-based CVD graphene manufacturer established in 2011 that produces graphene films on copper, SiO2/Si wafers and flexible polyethylene terephthalate (PET), and its largest film produced on copper that is available is 24 × 300 inch2. Bae et al. from Sungkyunkwan University in Korea first reported16 an R2R production method to produce large-area graphene TCFs 30 inches across in collaboration with Samsung in 2010. Today, several manufacturers of CVDgrown graphene film and equipment, such as Graphene Square, have been formed in Korea. In 2012, Sony developed a new R2R method17, which directly applied a current to heat a copper foil instead of using the traditional heating method14–16,18,19, and realized the production of graphene films more than 100 m in length. Although its research on graphene produced by CVD is a little behind the United States and Korea, China has made some important contributions such as the growth of large single crystals18, pure monolayers19, three-dimensional graphene networks21, and the non-destructive electrochemical bubbling transfer method18 that has already been used by some manufacturers. As potentially the biggest market for smart phones and one of the largest touch-panel manufacturing countries, the industrial production of largearea graphene films in China has developed very rapidly in the past 3 years. In January 2012, 2D Carbon Tech announced the first capacitive touch panel in the world based on graphene. In May 2013, it launched its b
© 2D CARBON TECH
of graphene sheets with an average thickness of 3 nm. Deyang Carbonene uses a proprietary intercalation–expansion– exfoliation technique12 and produces highquality pristine graphene sheets of fewer than 10 layers with a yield over 90 wt% and high electrical conductivity more than 1,000 S cm–1 (Fig. 2). A pilot production line with a capacity of 1.5 tonnes per year has been operating since October 2012, and a production line of 100 tonnes per year is under construction. Compared with mass production, the applications of small graphene sheets are still at an early stage. Almost every graphene manufacturing company has been attempting to use these materials for many purposes, ranging from energy storage, composites and functional coatings to electronics (Table 1). As China is one of the biggest lithium-ion battery manufacturing countries, in China lithium-ion batteries are the most explored application of small graphene sheets where graphene has been mainly used as a conductive additive in electrodes or as current-collector coatings. Because of their two-dimensional structure, high electrical conductivity and
Industrial production of large films
Figure 3 | Mass production and application of large-area graphene films. a, A large transparent conductive graphene film (about 20 × 20 cm2) manufactured by 2D Carbon Tech. b, Prototype of a mobile phone (2D Carbon Tech) using a graphene touch panel.
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COMMENTARY | FOCUS first commercial line, with a capacity of 30,000 m2 graphene films per year (Fig. 3), and the company is planning to reach 200,000 m2 by the end of 2014. In December 2013, Wuxi Graphene Film completed a production line with an annual output of 5 million graphene touch-screen products. PowerBooster realized the production of 60-inch graphene TCFs in 2012, and 7.5 m2 graphene films on copper and 3- to 20-inch single/multi-point touch panels in 2013.
Challenges and outlook
Although the large-scale production of graphene materials has been realized, many issues need to be addressed to advance their industrial applications. As any other product, the cost/performance ratio is the greatest concern for companies when determining whether graphene can be used in their products. To compete with existing materials, the cost of graphene is a big problem. Improving the controllability of mass production techniques to produce uniform graphene sheets, realizing direct growth of large-area, uniform, defect-free, few-layer graphene films on arbitrary
substrates at low temperatures, and the efficient, intact and clean transfer from metal substrates without sacrificing the metals so that they can be re-used are still challenges that need to be overcome. Methods for the sorting, modification, functionalization, stable doping and dispersion of graphene in various matrices are also required for its more universal use. Where and how far will graphene materials go, and when will graphene manufacturers start to make a profit from the material? The biggest challenge is to find ‘killer’ applications that demand a large quantity of graphene. Maintaining close collaboration with downstream application companies is necessary for the development of future applications. But no material can do everything, and graphene has to find its proper use. Graphene manufacturers must be very careful, when expanding their production scale, to ensure that there are appropriate uses for the material. ❐ Wencai Ren and Hui-Ming Cheng are at the Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese
Academy of Sciences, Shenyang 110016, China. e-mail: [email protected]; [email protected] References
1. Geim, A. K. Science 324, 1530–1534 (2009). 2. Wallace, P. R. Phys. Rev. 71, 622–634 (1947). 3. Novoselov, K. S. et al. Science 306, 666–669 (2004). 4. Segal, M. Nature Nanotech. 4, 612–614 (2009). 5. Zhu, Y. W. et al. Adv. Mater. 22, 3906–3924 (2010). 6. Novoselov, K. S. et al. Nature 490, 192–200 (2012). 7. Bonaccorso, F., Sun, Z., Hasan, T. & Ferrari, A. C. Nature Photon. 4, 611–622 (2010). 8. Paton, K. R. et al. Nature Mater. 13, 624–630 (2014). 9. Jeon, I. Y. et al. Proc. Natl Acad. Sci. USA 109, 5588–5593 (2012). 10. Stankovich, S. et al. Carbon 45, 1558–1565 (2007). 11. Schniepp, H. et al. J. Phys. Chem. 110, 8535–8539 (2006). 12. Pei, S. F. et al. Method for preparing high-quality graphene. Chinese patent ZL.201110282370.5 (2011). 13. Eda, G. & Chhowalla, M. Adv. Mater. 22, 2392–2415 (2010). 14. Kim, K. S. et al. Nature 457, 706–710 (2009). 15. Li, X. S. et al. Science 324, 1312–1314 (2009). 16. Bae, S. et al. Nature Nanotech. 5, 574–578 (2010). 17. Kobayashi, T. et al. Appl. Phys. Lett. 102, 023112 (2013). 18. Gao, L. B. et al. Nature Commun. 3, 699 (2012). 19. Dai, B. Y. et al. Nature Commun. 2, 522 (2011). 20. http://www.thomas-swan.co.uk/news/advanced-materials-news 21. Chen, Z. P. et al. Nature Mater. 10, 424–428 (2011).
Acknowledgements
We thank S. F. Pei, L. P. Ma and H. Bi for discussions, L. C. Yin for help with drawing the structural models in Fig. 1a, and NSFC (Nos. 51325205, 51290273, 51221264 and 51172240), MOST of China (No. 2012AA030303) and CAS (No. KGZD-EW-303-1) for support.
Challenges and opportunities in graphene commercialization Amaia Zurutuza and Claudio Marinelli As technical knowledge, manufacturing methods and the development of applications mature, key factors will affect the pace of commercialization of graphene.
I
t is now 10 years since the Nobel Prize winners Andre Geim and Konstantin Novoselov published the first 1 of a series of seminal papers that triggered a sharp rise in the level of graphene research efforts worldwide. Fuelled by public (for example, European Commission, UK and Korean governments) as well as private investments (for example, Samsung, IBM, Nokia), research on graphene has produced a substantial body of scientific knowledge, accompanied by a surge of publications and patent applications. The past 6–7 years have seen a steady, worldwide emergence of private ventures focused on the manufacturing and commercialization of graphene and graphene-based materials, with 44 companies currently active (Mark Rahn from MTI Venture, talk 730
given at Graphene: Commercialisation and Applications, Univ. of Manchester, 12–13 June 2014) and a range of these materials commercially available. Nevertheless, there are only a few graphene-based products that have reached the market, such as the tennis racket by Head, the battery strap by Vorbeck, the oildrilling mud by Nanochem or the phone touch screen by Samsung. These products represent an initial market entry rather than the first, full commercial wave of graphene products. The size of the graphene market was estimated2 to be around US$12 million in 2013, indicating that so far we are still in a phase of research and development, in which the market is dominated by sales of raw graphene materials. The market projections for the next 5–10 years, however, indicate
significant expansion and revenue increase. An increase in graphene demand should drive up production scale and drive down costs, resulting in a shift from material sales to a market dominated by sales of graphenebased components, systems and products. The steep rise in graphene application patents further supports the realization of an industrial graphene market in the upcoming years3. Figure 1 shows the comparison of the patent landscape of different materials. The number of graphene patents has increased significantly more steeply than for the other benchmark materials, including silicon (Fig. 1, inset). Progress in the commercialization of graphene can be assessed by looking at the growth of demand-driven graphene production (rather than production capacity)
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The global growth of graphene Wencai Ren and Hui-Ming Cheng The large-scale production of graphene aimed at industrial applications has grown significantly in the past few years, especially since many companies in China have entered the market.
G
raphene is the thinnest imaginable material and is highly transparent; it is the strongest material ever examined, the most stretchable crystal, the most impermeable material, even to helium; it has a record thermal conductivity 10 times as high as copper, and the highest intrinsic electron mobility, about 100 times that of silicon1. Graphene has been discussed theoretically since the 1940s2, but it took 60 years to experimentally obtain a few sheets of micrometre-sized high-quality flakes weighing picograms3. Yet, only 10 years since Geim and Novoselov first used adhesive tape to isolate graphene from graphite, graphene sheets are being produced in hundreds of tonnes and tens of thousands of square metres. Five years ago, only a few USAbased small start-up companies, such as Angstron Materials, Vorbeck Materials and XG Sciences, were making large volumes of small graphene sheets4. Since then, tens of graphene manufacturing companies have sprung up all over the world, which produce not only small graphene sheets but also large-area, high-quality graphene films on an industrial scale. In particular, the production industry of graphene materials in China has been developing very rapidly, and its total annual production capacity of small graphene sheets and graphene films exceeds 400 tonnes and 110,000 m2, respectively.
Mass production methods of graphene
Small sheets and large-area films are two major forms of graphene used for various applications. Small graphene sheets can be used in composites, functional coatings, conductive inks, batteries and supercapacitors5,6. Large-area graphene films can be used as transparent electrodes in touch panels, displays and photovoltaic devices with potentially low cost, and more importantly, they are expected to be used in next-generation electronics and optoelectronics such as flexible and wearable devices6,7. Exfoliation of bulk graphite (the topdown approach) is the most commonly used method for the mass production of small 726
graphene sheets. This can be through direct exfoliation in a liquid, with or without the use of a surfactant 8, or in the solid state by edge functionalization9, or by first inserting a chemical species between the graphene layers in graphite to weaken their interaction followed by exfoliation10–12 (Fig. 1a). Bottomup approaches such as substrate-free chemical vapour deposition (CVD) and solvothermal and combustion processes have also been developed. Depending on the strategy used, there are considerable differences in yield, efficiency, cost, accompanying pollution, ease of production and scalability of the manufacturing process, and in the morphology, structure and properties of the products such as thickness, lateral size, surface chemistry, solubility, defect and impurity contents, and electrical and thermal conductivities (Fig. 1 and Table 1). To produce uniform monolayer and few-layer graphene sheets with high yield and high efficiency is a universal challenge for all these mass production methods. Chemical assembly of small graphene sheets and CVD are two methods to produce large-area graphene films5,7,13–19 (Fig. 1b and Table 1). Chemical assembly can be easily realized on various substrates at low temperatures, but the films obtained suffer from poor quality, for example low electrical conductivity 5,7,13. CVD produces high-quality graphene films by the catalytic decomposition of hydrocarbons on a metal (for example, Cu, Ni, Pt or alloy) surface at high temperatures, and the films are then transferred to transparent substrates such as glass and polymers by etching away the metal or by non-destructive electrochemical bubbling for transparent conductive film (TCF) applications14–19. Roll-to-roll (R2R) CVD growth and transfer techniques have been developed to fabricate large-area TCFs16,17. Films produced over a large area, however, usually show performance inferior to high-end indium tin oxide films but with higher cost. How to realize direct growth of large-area uniform defect-free few-layer graphene films on arbitrary substrates, and how to transfer the films intact and cleanly
from a metal substrate without sacrificing it, so that it can be re-used, are two big challenges for the CVD production of highperformance, low-cost graphene TCFs.
Industrial production of small sheets
Exfoliation of graphite is the most widely used method for the industrial production of small graphene sheets (Table 1). Angstron Materials in the United States and Thomas Swan in the United Kingdom are two representative manufacturers that use direct liquid-exfoliation methods to produce high-quality pristine graphene materials. Thomas Swan’s first integrated process producing kilogram quantities per day will be up and running by September 201420. Although this process is easy to realize and scale up (graphene materials can even be produced using a kitchen blender 8), it produces a mixture of small-size monolayer or few-layer graphene sheets and even thin graphite flakes, and suffers from surfactant or organic solvent contamination. China’s graphene manufacturers mostly use oxidation–exfoliation–reduction10,11 and intercalation–exfoliation12 methods to produce small graphene sheets. The Sixth Element (Changzhou) Materials and Tianjin Plannano Technology use oxidation to form oxygen-containing functional groups covalently bonded with the graphene layer to weaken the interlayer interaction of graphite. Oxidation makes a dispersion of graphite oxide difficult to handle and to clean, resulting in low efficiency; it also leads to severe structural damage to the graphene layer and produces a lot of pollution. But the exfoliation of purified graphite oxide in water by stirring and sonication produces a water-soluble functional material, graphene oxide, which is easy to use for many applications. The graphene oxide is usually very thin and can be reduced to graphene, and defects and residual functional groups in the reduced graphene oxide are beneficial for applications such as catalysis, mechanically enhanced composites, and composite electrodes in batteries and supercapacitors. Sixth Element set up a mass production line with a capacity of
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FOCUS | COMMENTARY a
• Liquid exfoliation Pristine graphene sheets
Sonication, shearing, ball milling
Raw material: graphite
NMP, GBL, DMEU, DMF, IPA H2O + (sodium cholate, SDS, SDBS, PVA) • Solid exfoliation Nearly pristine graphene sheets
Edge-functionalized graphene Ball milling
Thermal annealing
Dry ice, oxalic acid
Ar, N2
• Oxidation–exfoliation–reduction Graphite oxide (Modified) Hummers, Brodie, Staudenmaier
Sonication, Graphene oxide, stirring functionalized graphene H2O, NMP, DMF, ethanol, THF, PC Rapid heating, microwave, arc discharge Ar, H2, air
NaNO3, KMnO4, H2SO4, KClO3, HNO3
Thermal annealing Ar and/or H2, vacuum Hydrothermal
Reduced graphene oxide
Chemical reaction Hydrazine, NaBH4, hydrazine hydrate, alcohols NaOH, KOH, VC, HI
• Intercalation–exfoliation Heating, stirring, electrochemical
Intercalated graphite
Sonication
Chemical reaction H2O, ethanol, H2O2, TBA
K, Cs, NaK2, K/THF, ClF3, ICl, IBr, FeCl3, Li/PC, H2SO4, eutectic salt, CSA, H2O2, ionic liquids
b
Small graphene sheets
Solid exfoliation Easy to realize Agglomeration, non-uniformity
H2O + SDBS, sodium cholate (aq.), ethanol, NMP, pyridine, DMF, CSA, DSPE-mPEG
Large-area graphene films Substrate CVD Large area Difficulty in growing large-area uniform quality multilayers on arbitrary substrates, and intact transfer from metals
Liquid exfoliation Intercalation–exfoliation Easy to realize High yield Low yield, small size, Usually thick, low concentration, non-uniformity non-uniformity, impurities
Quality
Pristine graphene sheets
Expanded graphite
Heating, microwave
Substrate-free CVD High purity Low yield, low efficiency, small size Assembly Low temperature, easy to realize, applicable for various substrates Low conductivity
Chemical reaction Oxidation– Small size, exfoliation–reduction low purity Easy to functionalize, processable Low efficiency, serious pollution
Cost
Figure 1 | Main mass production methods of graphene. a, Four typical methods for the mass production of small graphene sheets by exfoliation of bulk graphite. b, Comparison of the quality and cost of graphene products manufactured by different methods. NATURE NANOTECHNOLOGY | VOL 9 | OCTOBER 2014 | www.nature.com/naturenanotechnology
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COMMENTARY | FOCUS Table 1 | Basic synthesis method, product, production capacity and main application products of several big graphene manufacturers. Graphene Basic synthesis manufacturer method
Basic product
Production capacity
Main application products
Angstron Materials (USA)
Liquid exfoliation
Pristine nanographene platelets Thickness: 90%, 200–400 Ω per square at >85% transmittance (including substrate)
30,000 m2 (May 2013) 200,000 m2 (December 2014)
Touch panels
Wuxi CVD Graphene Film (China)
Graphene films on Cu, PET Film on PET: ~600 Ω per square at >97% transmittance (excluding substrate)
80,000 m2 (December 2013)
Touch panels, touch sensors (5 million pieces, December 2013)
PowerBooster (China)
Graphene films on Cu, PET Film on Cu: available maximum size 7.5 m2 (2013) Film on PET: 50–140 Ω per square at 95.5% transmittance
-
Touch panels
CVD
100 tonnes per year in 2013. The USA-based Vorbeck Materials uses similar technology to produce functionalized graphene with a unique wrinkled morphology 11. Ningbo Morsh Technology, Deyang Carbonene Technology and XG Sciences are using non-oxidation intercalation 728
to produce high-quality pristine graphene materials, which are suitable for applications requiring high electrical and thermal conductivity. This process is easier to scale up and more efficient, causes less pollution than the oxidation route and has a much higher yield than the
direct liquid-exfoliation route. However, the product is usually thick. XG Sciences reached an annual production capacity of 80 tonnes in 2012, and its product has an average thickness of ~2 to 15 nm. In 2013, Ningbo Morsh opened a production line with an annual output of 300 tonnes
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FOCUS | COMMENTARY a
b
c
d
100 nm
1 nm
Figure 2 | Mass production and application of small graphene sheets. a, A shipment of few-layer graphene product manufactured by Deyang Carbonene Technology. b, Graphene-coated aluminium current collectors for lithium ion batteries. c,d, Transmission electron micrograph (c) and aberration-corrected high-resolution transmission electron micrograph (d) of the product in a, showing its very high quality. Images: a, © Deyang Carbonene Technology; b, courtesy of Songfeng Pei; c,d, courtesy of Zhibo Liu.
impermeability, small graphene sheets have also been explored as antistatic and anticorrosion coatings. Developing thermal interfacial or heat-spreading materials that make use of graphene’s high thermal conductivity in electronics such as in mobile phones and light-emitting diodes is another application focus in China. a
The United States and Korea pioneered research on the CVD growth of graphene films14–16. Together with China and Japan, they are devoted to the industrial production of graphene films in this way. Bluestone Global Tech is a USA-based CVD graphene manufacturer established in 2011 that produces graphene films on copper, SiO2/Si wafers and flexible polyethylene terephthalate (PET), and its largest film produced on copper that is available is 24 × 300 inch2. Bae et al. from Sungkyunkwan University in Korea first reported16 an R2R production method to produce large-area graphene TCFs 30 inches across in collaboration with Samsung in 2010. Today, several manufacturers of CVDgrown graphene film and equipment, such as Graphene Square, have been formed in Korea. In 2012, Sony developed a new R2R method17, which directly applied a current to heat a copper foil instead of using the traditional heating method14–16,18,19, and realized the production of graphene films more than 100 m in length. Although its research on graphene produced by CVD is a little behind the United States and Korea, China has made some important contributions such as the growth of large single crystals18, pure monolayers19, three-dimensional graphene networks21, and the non-destructive electrochemical bubbling transfer method18 that has already been used by some manufacturers. As potentially the biggest market for smart phones and one of the largest touch-panel manufacturing countries, the industrial production of largearea graphene films in China has developed very rapidly in the past 3 years. In January 2012, 2D Carbon Tech announced the first capacitive touch panel in the world based on graphene. In May 2013, it launched its b
© 2D CARBON TECH
of graphene sheets with an average thickness of 3 nm. Deyang Carbonene uses a proprietary intercalation–expansion– exfoliation technique12 and produces highquality pristine graphene sheets of fewer than 10 layers with a yield over 90 wt% and high electrical conductivity more than 1,000 S cm–1 (Fig. 2). A pilot production line with a capacity of 1.5 tonnes per year has been operating since October 2012, and a production line of 100 tonnes per year is under construction. Compared with mass production, the applications of small graphene sheets are still at an early stage. Almost every graphene manufacturing company has been attempting to use these materials for many purposes, ranging from energy storage, composites and functional coatings to electronics (Table 1). As China is one of the biggest lithium-ion battery manufacturing countries, in China lithium-ion batteries are the most explored application of small graphene sheets where graphene has been mainly used as a conductive additive in electrodes or as current-collector coatings. Because of their two-dimensional structure, high electrical conductivity and
Industrial production of large films
Figure 3 | Mass production and application of large-area graphene films. a, A large transparent conductive graphene film (about 20 × 20 cm2) manufactured by 2D Carbon Tech. b, Prototype of a mobile phone (2D Carbon Tech) using a graphene touch panel.
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COMMENTARY | FOCUS first commercial line, with a capacity of 30,000 m2 graphene films per year (Fig. 3), and the company is planning to reach 200,000 m2 by the end of 2014. In December 2013, Wuxi Graphene Film completed a production line with an annual output of 5 million graphene touch-screen products. PowerBooster realized the production of 60-inch graphene TCFs in 2012, and 7.5 m2 graphene films on copper and 3- to 20-inch single/multi-point touch panels in 2013.
Challenges and outlook
Although the large-scale production of graphene materials has been realized, many issues need to be addressed to advance their industrial applications. As any other product, the cost/performance ratio is the greatest concern for companies when determining whether graphene can be used in their products. To compete with existing materials, the cost of graphene is a big problem. Improving the controllability of mass production techniques to produce uniform graphene sheets, realizing direct growth of large-area, uniform, defect-free, few-layer graphene films on arbitrary
substrates at low temperatures, and the efficient, intact and clean transfer from metal substrates without sacrificing the metals so that they can be re-used are still challenges that need to be overcome. Methods for the sorting, modification, functionalization, stable doping and dispersion of graphene in various matrices are also required for its more universal use. Where and how far will graphene materials go, and when will graphene manufacturers start to make a profit from the material? The biggest challenge is to find ‘killer’ applications that demand a large quantity of graphene. Maintaining close collaboration with downstream application companies is necessary for the development of future applications. But no material can do everything, and graphene has to find its proper use. Graphene manufacturers must be very careful, when expanding their production scale, to ensure that there are appropriate uses for the material. ❐ Wencai Ren and Hui-Ming Cheng are at the Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese
Academy of Sciences, Shenyang 110016, China. e-mail: [email protected]; [email protected] References
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Acknowledgements
We thank S. F. Pei, L. P. Ma and H. Bi for discussions, L. C. Yin for help with drawing the structural models in Fig. 1a, and NSFC (Nos. 51325205, 51290273, 51221264 and 51172240), MOST of China (No. 2012AA030303) and CAS (No. KGZD-EW-303-1) for support.
Challenges and opportunities in graphene commercialization Amaia Zurutuza and Claudio Marinelli As technical knowledge, manufacturing methods and the development of applications mature, key factors will affect the pace of commercialization of graphene.
I
t is now 10 years since the Nobel Prize winners Andre Geim and Konstantin Novoselov published the first 1 of a series of seminal papers that triggered a sharp rise in the level of graphene research efforts worldwide. Fuelled by public (for example, European Commission, UK and Korean governments) as well as private investments (for example, Samsung, IBM, Nokia), research on graphene has produced a substantial body of scientific knowledge, accompanied by a surge of publications and patent applications. The past 6–7 years have seen a steady, worldwide emergence of private ventures focused on the manufacturing and commercialization of graphene and graphene-based materials, with 44 companies currently active (Mark Rahn from MTI Venture, talk 730
given at Graphene: Commercialisation and Applications, Univ. of Manchester, 12–13 June 2014) and a range of these materials commercially available. Nevertheless, there are only a few graphene-based products that have reached the market, such as the tennis racket by Head, the battery strap by Vorbeck, the oildrilling mud by Nanochem or the phone touch screen by Samsung. These products represent an initial market entry rather than the first, full commercial wave of graphene products. The size of the graphene market was estimated2 to be around US$12 million in 2013, indicating that so far we are still in a phase of research and development, in which the market is dominated by sales of raw graphene materials. The market projections for the next 5–10 years, however, indicate
significant expansion and revenue increase. An increase in graphene demand should drive up production scale and drive down costs, resulting in a shift from material sales to a market dominated by sales of graphenebased components, systems and products. The steep rise in graphene application patents further supports the realization of an industrial graphene market in the upcoming years3. Figure 1 shows the comparison of the patent landscape of different materials. The number of graphene patents has increased significantly more steeply than for the other benchmark materials, including silicon (Fig. 1, inset). Progress in the commercialization of graphene can be assessed by looking at the growth of demand-driven graphene production (rather than production capacity)
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