Effects of Current Annealing on Thermal Conductivity of Carbon Nanotubes

This work documents the annealing effect on the thermal conductivity of nanotube film (CNTB) and carbon nanotube fiber (CNTF). The thermal properties of carbon nanotube samples are measured by using the transient electro-thermal (TET) technique, and the experimental phenomena are analyzed based on numerical simulation. During the current annealing treatment, CNTB1 always maintains the negative temperature coefficient of resistance (TCR), and its thermal diffusivity increases gradually. When the annealing current is 200 mA, it increases by 33.62%. However, with the increase of annealing current, the TCR of CNTB2 changes from positive to negative. The disparity between CNTB2 and CNTB1 suggests that they have different physical properties and even structures along their lengths. The high-level thermal diffusivity of CNTB2 and CNTF are 2.28–2.46 times and 1.65–3.85 times higher than the lower one. The results show that the decrease of the thermal diffusivity for CNTB2 and CNTF is mainly caused by enhanced Umklapp scattering, the high thermal resistance and torsional sliding during high temperature heating.

Hydrophilic and Conductive Carbon Nanotube Fibers for High-Performance Lithium-Ion Batteries

Carbon nanotube fiber (CNTF) is a highly conductive and porous platform to grow active materials of lithium-ion batteries (LIB). Here, we prepared SnO2@CNTF based on sulfonic acid-functionalized CNTF to be used in LIB anodes without binder, conductive agent, and current collector. The SnO2 nanoparticles were grown on the CNTF in an aqueous system without a hydrothermal method. The functionalized CNTF exhibited higher conductivity and effective water infiltration compared to the raw CNTF. Due to the enhanced water infiltration, the functionalized CNTF became SnO2@CNTF with an ideal core–shell structure coated with a thin SnO2 layer. The specific capacity and rate capability of SnO2@-functionalized CNTF were superior to those of SnO2@raw CNTF. Since the SnO2@CNTF-based anode was free of a binder, conductive agent, and current collector, the specific capacity of the anode studied in this work was higher than that of conventional anodes.

Commercial Wet-Spun Singlewall and Dry-Spun Multiwall Carbon Nanotube Fiber Surface O-Functionalization by Ozone Treatment

In this work, we demonstrate controlled introduction of O-functional groups on commercial carbon nanotube fibers (CNTFs) with different nanotube morphologies obtained by dry- and wet-spinning by treatment with gaseous ozone (O3(g)). Our test samples were (1) wet-spun fibers of smalldiameter (1–2 nm) singlewall (SW)-CNTs and (2) dry-spun fibers containing large-diameter (20 nm) multiwall (MW)-CNTs. Our results indicate that SW-CNTFs undergo oxygenation to a higher extent than MW-CNTFs due to the higher reactivity of SW-CNTs with a larger curvature strain. Oxygenation resulting from O3 exposure was evidenced as increase in surface O atomic% (at% by X-ray photoelectron spectroscopy, XPS) and as reductions in G/D (by Raman spectroscopy) as well as electrical conductivities due to changes in nanotube graphitic structure. By XPS, we identified the emergence of various types of O-functionalities on the fiber surfaces. After long duration O3 exposure (>300 s for SW-CNTFs and >600 s for MW-CNTFs), both sp2 C═O (carbonyl) and sp3 C–O moieties (ether/hydroxy) were observed on fiber surfaces. Whereas, only sp3 C–O (ether/hydroxy) components were observed after shorter exposure times. O3 treatment led to only changes in surface chemistry, while the fiber morphology, microstructure and dimensions remained unaltered. We believe the surface chemistry controllability demonstrated here on commercial fibers spun by different methods containing nanotubes of different structures is of significance in aiding the practical application development of CNTFs.