Method of Large Scale Fabrication of Continuous CNT Cable/ Sheet with High Conductivity and Stability

Introduction

This invention offers a novel technique to fabricate large-scale, lightweight electrically conductive cable using carbon nanotubes (CNTs). CNTs have good intrinsic electrical conductivity. However, entangled structures of CNTs in the form of yam or sheet has lower conductivity due to intertube contact resistance and gaps in between. Lightweight and high electrically conductive CNT materials can be used for cables for such applications as signal or power transmission, electromagnetic interference (EMI) shielding in electronic devices and lightning protection in aircraft etc.

An integrated approach of three major steps was used to improve the CNT sheet conductivity:

1) Mechanical stretching of entangled CNT sheets provides CNT alignment. Random and pristine CNT sheets in rolls were continuously stretched producing narrow and densely packed CNT networks, which reduced intertube contact resistance. With increased alignment, conductivity improved two or three times higher compared to the pristine, randomly aligned CNT sheets. This process can be performed continuously and scale-up production is possible.

2) A doping approach increases the carrier concentration of CNTs. For this purpose, vapor phase iodine doping was adopted, which can be expanded to other oxidizing liquids (acids such as HNO3, HCI or SOCh). Upon this chemical doping process, conductivity improved 3-4 times and a final room temperature conductivity of 10,000 Siem (up to 13,000 Siem). The doping process is a typical diffusion process and conductivity saturated after several hours, and its speed is depended on the packing of CNTs and mobility of the dopant and followed by time.

3) An approach to coating dramatically increased the cable stability. After doping process, the dopants are diffused out and kept inside the CNT yams/sheets to maintain the conductivity. For this purpose, doped CNT sheets were dipped in air stable conducting polymer, poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate)(PEDOT:PSS). The thin polymer coating on the surface provides synergetic effects for the conductivity and a protection layer. Different polymer layers, such as polyvinyl ch loride, polyethylene and rubber can also be used as protection layers as for conventional cables.

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Abstract
Claims

Provided herein are composite materials and methods of making composite materials including carbon nanoscale fiber networks . The composite materials may include a stretched and doped carbon nanoscale fiber network and a capping layer . The methods of making the composite mate rials may include stretching a carbon nanoscale fiber net work , contacting the nanoscale fiber network with a dopant , and disposing a capping layer on a surface of the carbon nanoscale fiber network.

We claim:

1. A method of making a composite material, the method comprising:

providing a carbon nanoscale fiber network which comprises a plurality of randomly oriented carbon nanoscale fibers;

stretching the carbon nano scale fiber network to align at least a portion of the plurality of randomly oriented carbon nanoscale fibers, thereby forming an aligned carbon nano scale fiber network, wherein the stretching of the carbon nano scale fiber network imparts the carbon nano scale fiber network with a stretch ratio of about 10% to about 70%;

rolling the aligned carbon nanoscale fiber network, pressing the aligned carbon nano scale fiber network, or rolling and pressing the aligned carbon nano scale fiber network prior to the contacting of the aligned carbon nano scale fiber network with a dopant;

contacting the aligned carbon nano scale fiber network with the dopant under conditions that cause at least a portion of the dopant to (i) adsorb to one or more surfaces of the aligned carbon nano scale fiber network, and (ii) penetrate the aligned carbon nano scale fiber network, thereby forming a doped carbon nano scale fiber network; and

disposing a capping layer on at least a surface of the doped carbon nano scale fiber network.

2. The method of claim 1, wherein the stretching of the carbon nano scale fiber network and the contacting of the aligned carbon nano scale fiber network with the dopant is effective to increase the electrical conductivity of the carbon nano scale fiber network comprising the plurality of randomly oriented carbon nano scale fibers by at least 10×.

3. The method of claim 1, wherein after the contacting of the aligned carbon nanoscale fiber network with the dopant, the dopant of the doped carbon nanoscale fiber network is present in an amount of about 10% to about 25% by weight, based on the total weight of the plurality of carbon nanoscale fibers and the dopant.

4. The method of claim 1, wherein the dopant comprises an oxidant.

5. The method of claim 4, wherein the oxidant is selected from I₂, ICl, SOCl₂, HNO₃, HCl, or a combination thereof.

6. The method of claim 1, wherein the contacting of the aligned carbon nanoscale fiber network with the dopant occurs at a temperature sufficient to sublimate the dopant.

7. The method of claim 1, wherein the stretch ratio is about 25% to about 45%.

8. The method of claim 1, wherein the doped carbon nanoscale fiber network is a sheet or a ribbon, and the capping layer is disposed substantially evenly on both sides of the sheet or the ribbon, respectively.

9. The method of claim 1, wherein the capping layer comprises a conductive polymer.

10. The method of claim 9, wherein the conductive polymer comprises PEDOT:PSS.

11. The method of claim 1, wherein the disposing of the capping layer on the doped carbon nanoscale fiber network comprises submerging at least a portion of the doped carbon nanoscale fiber network in a liquid comprising a conductive polymer.

12. The method of claim 1, wherein the plurality of randomly oriented carbon nanoscale fibers comprises single-wall carbon nanotubes, multi-wall carbon nanotubes, or a combination thereof.

13. The method of claim 1, wherein the plurality of randomly oriented carbon nanoscale fibers comprises functionalized carbon nanoscale fibers.

14. A method of making a composite material, the method comprising:

providing a carbon nanoscale fiber network which comprises a plurality of randomly oriented carbon nanotubes;

stretching the carbon nano scale fiber network to align at least a portion of the plurality of randomly oriented carbon nanotubes to form a stretched carbon nano scale fiber network, wherein the stretching of the carbon nano scale fiber network imparts the carbon nanoscale fiber network with a stretch ratio of about 10% to about 70%;

rolling the stretched carbon nanoscale fiber network, pressing the stretched carbon nano scale fiber network, or rolling and pressing the stretched carbon nano scale fiber network prior to the contacting of the stretched carbon nano scale fiber network with a dopant;

contacting the stretched carbon nano scale fiber network with the dopant to form a doped carbon nano scale fiber network, the contacting occurring under conditions that sublimate the dopant, and cause the dopant to (i) adsorb to one or more surfaces of the stretched carbon nano scale fiber network, (ii) penetrate the stretched carbon nano scale fiber network, or (iii) a combination thereof; and

submerging at least a portion of the doped carbon nano scale fiber network in a mixture comprising a liquid and a capping layer to dispose the capping layer on at least a surface of the doped carbon nano scale fiber network, wherein the capping layer comprises a conductive polymer;

wherein the stretching of the carbon nano scale fiber network and the contacting of the stretched carbon nano scale fiber network with the dopant is effective to increase the electrical conductivity of the carbon nano scale fiber network comprising the plurality of randomly oriented carbon nanotubes by at least 10×.

Title

CARBON NANOSCALE FIBER - BASED MATERIALS AND METHODS

Inventor(s)

Zhiyong Liang, Jin Gyu Park, Songlin Zhang, Ayou Hao

Assignee(s)

Florida State University Research Foundation , Inc.

Patent #

10586629

Patent Date

March 10, 2020