Tolerancia a la frustración: capacidad para digerir los fracasos y soportar las

Here, recent advances regarding CNT-based non-metal conductors have been

comprehensively reviewed with an emphasis on potential use as lightweight, flexible, and environmental resistance alternative conductors compared to metal. The main theme addressed the electrical conduction performance, fabrication methods, and potential

applications. Although single CNTs with specific chirality and shorter lengths demonstrated high electrical conductivity, a significant issue currently lies in transferring those excellent properties from the nanoscale to the macroscale of CNT assemblies (i.e. fibers and films). Nevertheless, the advantages of CNT conductors over traditional metal conductors are obvious, including low density, better environmental stability, excellent mechanical performance and ultrahigh electrical conductivity. CNT conductors delivered the best compromise in terms of specific conductivity and strength. Despite the great success of improving CNT assemblies to achieve high conductivity, several challenges still exist that impede large-scale production and engineering applications. Those challenges include: (1) achieving high conductivity of the individual CNT at macroscale, (2) developing cost- effective manufacturing methods, (3) establishing long-term stability of highly conductive performance, and (4) developing scale-up production capabilities with good quality control. These issues require further study before CNT conductors can be transferred into real-world engineering application.

Several potential strategies could be further developed to achieve the ultimate goal of using CNT as the next generation non-metal electrical conductors to potentially replace traditional metals for many applications First, understanding and optimizing the contact resistance between neighboring nanotubes is required to harness the overall high resistance of CNT assemblies. Different contact enhancers can be explored, such as nanocarbons (e.g.: graphene, and pyrolyzed polydopamine), conductive polymers (e.g.: PEDOT:PSS) and

This article is protected by copyright. All rights reserved. 83

nanometal particles or films. One principle when dealing with these contact enhancers is to incorporate just enough enhancers to achieve the minimum contact resistance. Secondly, better control over the alignment of CNTs could greatly enhance the electrical, mechanical, and thermal properties of fibers and films because of the enhanced contacts and the

concomitant better interactions between neighboring nanotubes. Thus, a dense packing structure of aligned nanotubes is desired and promises to be very effective when coupled with other contact enhancers, chemical and physical post-treatments. Finally, a continuous

manufacturing method that embraces aspects mentioned above is critical for the realization of CNT conductors for commercial applications.

Despite the several challenges, the high specific electrical conductivity of CNT fibers has already been reported to be much higher that of copper, demonstrating the excellent potential of CNTs to replace traditional metal conductors. Inspired by these successes, CNT fibers and films with scale-up size can be potentially fabricated with high electrical conductivity

through a better control of alignment, dense packing structure, and low contact resistance, which represents the major methods toward approaching the theoretical conductivity of individual CNTs. We believe that the development of further improved high conductivity of CNT conductors will promote the real-world applications as alternatives to metal conductors.

Acknowledgements

This work was partially supported by AFOSR FA9550-17-1-0005. Songlin Zhang also thanks Yinnan Zhang for the fruitful discussions on summary graphs drawing and plotting, and the support from China Scholarship Council (CSC no. 201506630022).

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