Y. Dini, J. Faure-Vincent, J. Dijon
CEA (Commissariat à l'énergie atomique et au énergies alternatives),
Keywords: carbon nanotube, yarn, annealing, doping
Summary:In electrical wiring, metal substitution by high conductivity materials like carbon nanotubes (CNT) is a near future challenge for high-end textile , aeronautic and aerospace applications . Several techniques exist to make CNT yarns. The most suitable, eco-friendly process for large-scale production is to directly dry spin CNTs grown by fixed- or floating-catalyst Chemical Vapor Deposition (CVD) (see Figure 1). However, the CNT yarn conductivity does not yet reach that of copper. Our work aims to overcome the 1.0 mΩ.cm resistivity limitation faced by all CNT yarns spun from CNT arrays in the literature. In our previous work , we found that, at room temperature, the electrical conductivity of the CNT yarn spun from CNT arrays is limited by the intrinsic conductivity of the CNTs and we insisted on the crucial need to increase the CNT structural quality. We will present our last work where we significantly increase the CNT yarn conductivity by doping and annealing treatments. At CEA Grenoble, we developed a new p-type dopant for carbon nanotubes and graphene: platinum chloride IV (Patent: US20180142346). It shows very good performances in term of conductivity improvement, temperature stability and long term time stability. Our dopant improves the CNT yarn and web electrical transport. The resistivity is considerably decreased by a factor of almost 3 and the stability in room condition is excellent. The doped CNT web resistivity only increases by 15 % in 136 days (see Figure 2). The very long term time stability of the platinum chloride makes it a very efficient dopant from an industrial point of view. The CNT structural quality is increased by annealing our CNT yarn at temperature between 2000 °C and 2500 °C and for durations up to 72 h . We observe a large improvement in the CNT structural quality as shown by the Raman G/D ratio which increases from 1.5 for a pristine yarn to more than 10 for an 11 hours annealing time at 2250 °C (see Figure 3.a). We find that the CNT resistivity decreases with the increase of G/D ratio i.e. with the increase of the CNT structural quality. The CNT yarn resistivity is clearly improved by the annealing at very high temperature: it decreases by a factor of 2, going from 1.6 mΩ.cm to 0.76 mΩ.cm (see Figure 3.b). This low resistivity value is the new world record for undoped CNT yarn spun from arrays (usually limited between 1 and 3 mΩ.cm).  C. Wang, et al., Adv. Mater. (2018) 1801072.  P. Jarosz, et al., Nanoscale. 3 (2011) 4542.  Y. Dini, J. Faure-Vincent, J. Dijon, How to overcome the electrical conductivity limitation of carbon nanotube yarns drawn from carbon nanotube arrays, (submitted to Carbon), (2018).  R. Andrews, et al., Carbon. 39 (2001) 1681–1687.