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| Fig. 1: Carbon Nanotube Structure. (Source: Wikimedia Commons) |
Nanotechnology has been a point of focus in the energy sphere as a potential way to improve systems and increase efficiency. One such example is carbon nanotubes, which are ultra-thin tubes of rolled-up graphene. Carbon nanotubes are a relatively modern finding, discovered in 1991. [1] They have not been widely implemented as of yet, given the high energy and economic cost of production, but are being researched for their applications in various fields, including energy storage. Many researchers believe that nanotubes have potential in energy technology given their unique physical, thermal and electrical properties, though there is still uncertainty about real world feasibility.
Carbon nanotubes have a structure composed of carbon atoms in a hexagonal lattice formation, rolled into a thin tube, with diameters that can vary but measured in the scale of nanometers. They could have one or many walls, with a length at least 1000 times their width. (See Fig. 1 for single layered nanotube structure.) Nanotubes have been considered for their applications in energy due to their high specific surface area and high ionic conductivity, which could be beneficial to improving battery storage and power. [2] Shorter nanotubes with larger diameters were found to be able to store more energy, since the ions can exit more easily. In longer, thinner nanotubes the ions are more likely to get stuck and bounce around indefinitely. [3]
Current research in this area is quite preliminary.
A recent (2024) study proposed using twisted nanotube ropes to store energy. The nanotubes were found to be relatively stable under temperature conditions ranging from -76 to 212 degrees Fahrenheit, able to preserve energy effectively, while lithium-ion batteries may be less resistant to temperatures at the extremes of this range. [4]
A 2009 study found that nanotubes have potential for use in anodes of batteries, given that their tests found that batteries with nanotubes incorporated had a high discharge and charge rate, and high recharge capacity retention, though another study (discussed below), found that this would not be energy efficient. [5]
For reasons of cost, much of the research in this area suggests that nanotubes should not exist as the primary material in energy storage devices, but supplement other solutions to improve efficiency by increasing surface area and conductivity. For example, it has been suggested that carbon nanotubes should be used as electrode additive to improve conductivity and allow for faster ion accessibility and diffusion. Another possibility is to add carbon nanotubes to microstructures in the battery to enhance surface area while contributing a low additional volume. [6]
A primary concern is the complexity of synthesis and energy cost of producing nanotubes.
Carbon nanotubes are both cost and energy intensive, depending on the mechanisms used to make them and subsequently the quality of the output. They are created in extremely high heat, using plasma or laser techniques and require high levels of energy to produce. Less resource-intense methods are available, such as chemical vapor decomposition, but these often result in lower quality nanotubes, which remove some of beneficial properties. [2,3] The highest quality nanotubes can cost tens or even hundreds of thousands of dollars per ton. [7]
A study that used Monte Carlo Simulation found that the energy cost of incorporating carbon nanotubes is outweighed by the benefits for cathodes, resulting in a total net benefit of 2775 MJ over its life cycle, but it is currently inefficient to incorporate into anodes, resulting in a net loss of 14,716 megajoules. [8]
There is also some research within the area of producing green nanotubes, or nanotubes that are created using sustainable methods. Research has explored using CO2 compounds, biological materials and microwave radiation to produce nanotubes, though none have been widely implemented as of yet. [9]
Overall, nanotubes have potential in the field of energy technology for storage and battery applications, but until the cost and difficulty of producing them is mitigated, they will remain a technology with, at best, only minimal uses in the area.
© Divya Bhojraj. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] J. Chen, S. Wei, and H. Xie, "A Brief Introduction of Carbon Nanotubes: History, Synthesis, and Properties," J. Phys. Conf. Ser. 1948, 012184 (2021).
[2] A. Aqel et al., "Carbon Nanotubes, Science and Technology Part (I) Structure, Synthesis and Characterisation," Arab. J. Chem. 5, 1 (2012).
[3] R. Amin, P. R. Kumar, and I. Belharouak, "Carbon Nanotubes: Applications to Energy Storage Devices," in Carbon Nanotubes - Redefining the World of Electronics, ed. by P. K. Ghosh, K. Datta and A. D. Rushi (InechOpen, 2021.
[4] S. Utsumi et al., "Giant Nanomechanical Energy Storage Capacity in Twisted Single-Walled Carbon Nanotube Ropes," Nat. Nanotechnol. 19, 1007 (2024).
[5] Y. He et al., "Structure and Electrochemical Performance of Nanostructured Fe3O4/Carbon Nanotube Composites as Anodes For Lithium Ion Batteries," Electrochim. Acta 55, 1140 (2010).
[6] L. Sun et al., "Roles of Carbon Nanotubes in Novel Energy Storage Devices," Carbon 122, 462 (2017).
[7] P. Sehrawat, C. Julien, and S. S. Islam, "Carbon Nanotubes in Li-Ion Batteries: A Review," Mater. Sci. Eng. B 213, 12 (2016).
[8] P. Zhai et al., "Net Energy Benefits of Carbon Nanotube Applications," Appl. Energy 173, 624 (2016).
[9] D. Janas, "From Bio to Nano: A Review of Sustainable Methods of Synthesis of Carbon Nanotubes," Sustainability 12, 4115 (2020).
