Carbon Nanotube Macro-films Research Articles

Ni-modified carbon nanotube macrofilms supporting NiFe with stable structure for efficient oxygen evolution reaction

The CMF-Ni substrate with high hydrophilicity and good electrical conductivity can induce spherical NiFe particles with strong structure to tightly anchor on the CMF surface, demonstrating fast charge-transfer kinetics and good cycling stability. • Ni-modified CMF presented increased hydrophilicity and electrical conductivity. • The CMF-Ni substrate could induce spherical NiFe to tightly anchor on CMF surface. • NiFe particles were encapsulated with oxyhydroxide (NiFeOOH) thin layers. • The binder-free NiFe/CMF-Ni electrode exhibited enhanced cycling stability. • Excellent activity was ascribed to the strong interaction between NiFe and CMF-Ni. A substrate with good hydrophilicity and conductivity is essential to design a binder-free efficient catalyst for oxygen evolution reaction (OER). In this work, We introduced Ni particles onto one side of the carbon macro-film (CMF) surface (CMF-Ni) via electrodeposition method. The hydrophilicity and conductivity of the CMF-Ni could be increased sharply compared to the CMF. And then spherical NiFe particles could be tightly anchored on the CMF side of the CMF-Ni substrate. Compared to the NiFe/CMF with flower-like structure prepared by using bare CMF as a substrate, the obtained NiFe/CMF-Ni with sandwich structure could be directly used as a binder-free electrode and exhibited higher stability and faster catalytic reaction kinetics. There is no obvious change of morphology and microstructure for the NiFe/CMF-Ni electrode after OER stability test at 1.54 V@50 mA cm −2 after 24 h. The main reasons for this result are that NiFe particles are mainly encapsulated with NiFeOOH thin layers and intertwined with carbon nanotubes, thereby possessing good corrosion resistance. This work not only fabricates an efficient binder-free electrode but also more importantly provides a facile substrate strategy, which can pave the way for effective integrated electrodes fabricating and their stability boosting.

Potential threshold of anode materials for foldable lithium-ion batteries featuring carbon nanotube current collectors

Flexible carbon nanotube macro-films (CMFs) are perfect current collectors for preparing foldable lithium-ion batteries (LIBs). However, selecting appropriate anodes for electrode is difficult because of the different potentials (vs. Li/Li+) of carbon nanotubes and traditional metallic current collector. This study demonstrated an additional reaction at potential below 0.9 V (vs. Li/Li+) caused by CMF, And Li+ will be constrained, which decreased capacity of anode/CMF electrode. Conversely, results changed when the anode potential exceeded 0.9 V (vs. Li/Li+) because Li+ passed the potential threshold, and the CMF retained its electrochemical inactivity. Consequently, the CMF-based foldable LIBs performed well. The potential threshold mechanism of anode is expected to provide new impetus to both academia and industry for exploring flexible or foldable LIBs.

Electromagnetic interference shielding effectiveness of composite carbon nanotube macro-film at a high frequency range of 40 GHz to 60 GHz

The electromagnetic interference (EMI) shielding effectiveness (SE) of carbon nanotube (CNT) macro-film that is adhered to common cloth to maintain the light weight, silk-like quality, and smooth surface of the material for EMI shielding is investigated. The results show that a high and stable EMI SE of 48 dB to 57 dB at 40 GHz to 60 GHz was obtained by the macro-film with a thickness of only ∼4 μm. The composite CNT macro-film is easily manipulated, and its EMI property is significantly different from that of traditional electromagnetic shielding materials that show a lower EMI SE with increasing frequency. For example, the EMI SE of Cu foils decrease from 75 dB to 35 dB as frequency increases from 25 GHz to 60 GHz. Considering their stable and outstanding EMI SE and easy manipulation, the composite CNT macro-films are expected to have potential applications in shielding against millimeter waves.

Folding insensitive, high energy density lithium-ion battery featuring carbon nanotube current collectors

Here we report a fully foldable lithium-ion battery (LIB) with high energy density using Li4Ti5O12 (LTO) as the anode and LiCoO2 (LCO) as the cathode with free standing carbon nanotube (CNT) Macro-Films (CMF) as the current collectors. The CMFs were produced using a scalable Floating Catalyst Chemical Vapor Deposition method. The highly flexible CMFs could be folded multiple times without plastic deformation. Importantly the active material (LTO in case of the anode or LCO in case of the cathode) infiltrates into the pores of the CMF forming a strong interface that is resistant to delamination even when the battery is folded repeatedly. Not only does the CMF impart shape conformality it also significantly boosts the energy density of the device. This is because the CMF is significantly lighter than conventional metal current collectors. We show that the energy density of the fully foldable battery with CMF current collectors can be up to ∼2-fold higher than conventional LIBs at realistic mass loading (∼5mgcm−2) of the electrode materials.

In-Situ Growth of LiMn2O4 Nanocrystals Embedded in Three-Dimension Single-Walled Carbon Nanotube Macrofilms as Stretchable Composite Cathode for Lithium-Ion Batteries

Electrode materials with total flexibility including not only the bendability but also the stretchability play the key roles in the emerging stretchable energy storage devices especially for the stretchable lithium-ion batteries (LIB). Herein, a stretchable composite for LIB cathode was fabricated by in-situ growth of LiMn2O4 (LMO) nanocrystals in the 3D macrofilms of single-walled carbon nanotube (SWNT) network via a low-temperature hydrothermal synthesis. Tomographic cross sections by focus ion beam (FIB) reveals the homogenous embedment of LMO nanocrystals spreading over the entire SWNT scaffold. X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) have confirmed the strong chemical bonding between LMO and the carboxyl groups on activated CNT surface through the in-situ growth. Such intense interactions ensure the mechanical property and electrical conductivity inherited from SWNT. The as-prepared 3D composites could be laminated with elastomeric substrate such as polydimethylsiloxane (PDMS) to form stretchable cathodes with full flexibility. The electrochemical performance of the freestanding LMO-SWNT macrofilm composite has been evaluated by galvanostatic charge-discharge cycling measurements, cyclic voltammetry and electrochemical impedance spectroscopy in CR2032 coin-cell configuration with lithium metals. The capacity retention exhibits a decreasing specific discharge capacity from initial 120 mAhg-1 approaching more stable to 100 mAhg-1 at the rate of 0.1 C (~ 15 mAg-1) for over 250 cycles. Correspondingly the Coulombic efficiency starts increasing from about 70% to over 95% at the end of cycling. Then the potential intermittent titration technique (PITT) was employed to analyze the Li+ chemical diffusivity of the freestanding composite related to the electrochemical performance. This present work provides a necessarily preliminary examination on the feasibility of the stretchable cathode before developing the fully stretchable LIB in the future.

Fragmentation of Carbon Nanotube Macro-Films By Ultrasound As Conductive Binder for Lithium-Ion Batteries

Fragmentation carbon nanotube macro-films (FCNT) with the structure of irregular laterally 2-D distributed CNT segments is found not only have high conductivity but also adhesive force. A conceptual idea to exploit FCNT alone as both binder and conductive additive for lithium-ion batteries was first-time proposed and demonstrated by constructing composite electrodes with a typical positive material, LiMn2O4 (LMO), in half cells. The new composite electrodes exhibit superior high-rate capabilities compared to the electrodes employing conventional binder, poly(vinylidene fluoride) (PVDF), and carbon black (CB). LMO with 30 wt% FCNT has specific capacity as high as 100 mAgh-1 at 150 mAg-1 and 78 mAhg-1 at 1500 mAg-1, which are about 87% and 70% of the 115 mAhg-1 at an extremely low current density of 15 mAg-1. In the contrast, the capacity of LMO with 15 wt% PVDF and 15 wt% CB drops over 55% of the initial capacity 87 mAhg-1 when the current density rises 100 times from 15 mAg-1 to 1500 mAg-1. Electrochemical impedance spectra indicate 30 wt% FCNT contributes both the lowest series and charge transfer resistance out of the electrodes with 5 wt%, 15 wt% and 30 wt% FCNT, which determine its best high-rate performance. LMO with 30 wt% FCNT also maintains 100% retention for 100 cycle at 150 mAg-1. An in-situ tribology method combining the wear track imaging and force measurement (shown in Figure 1) is introduced to evaluate the adhesion strength of electrodes comprising LMO with different mass fractions of FCNT and PVDF. The results show LMO with 30 wt% has adhesion strength of 7-10 MPa on the aluminum substrate which is at least comparable with the 6.3-8 MPa of 30 wt% PVDF. In addition, we further confirm the feasibility of this concept in two demo-systems, the half cells involving the negative materials Li4Ti5O12 (LTO) and the full cells combining LMO-FCNT as cathodes with LTO-FCNT as anodes. FCNT could be a competent substitute for polymer binders and conductive additives to maintain mechanical integrity and electrical connectivity of active materials in the composite electrodes.

Fragmented Carbon Nanotube Macrofilms as Adhesive Conductors for Lithium-Ion Batteries

Polymer binders such as poly(vinylidene fluoride) (PVDF) and conductive additives such as carbon black (CB) are indispensable components for manufacturing battery electrodes in addition to active materials. The concept of adhesive conductors employing fragmented carbon nanotube macrofilms (FCNTs) is demonstrated by constructing composite electrodes with a typical active material, LiMn2O4. The adhesive FCNT conductors provide not only a high electrical conductivity but also a strong adhesive force, functioning simultaneously as both the conductive additives and the binder materials for lithium-ion batteries. Such composite electrodes exhibit superior high-rate and retention capabilities compared to the electrodes using a conventional binder (PVDF) and a conductive additive (CB). An in situ tribology method combining wear track imaging and force measurement is employed to evaluate the adhesion strength of the adhesive FCNT conductors. The adhesive FCNT conductors exhibit higher adhesion strength than PVDF. It has further been confirmed that the adhesive FCNT conductor can be used in both cathodes and anodes and is proved to be a competent substitute for polymer binders to maintain mechanical integrity and at the same time to provide electrical connectivity of active materials in the composite electrodes. The organic-solvent-free electrode manufacturing offers a promising strategy for the battery industry.

A perspective: carbon nanotube macro-films for energy storage

The ever-increasing demand of electricity storage is a growing challenge among a broad range of renewable energy sources. The development of high-energy storage devices has been one of the most important research areas in modern days. In particular, rechargeable batteries and electrochemical capacitors are recognized as the primary power sources for applications from portable electronic devices to electric vehicles. In order to power the emerging flexible/stretchable electronics, power sources themselves must be able to accommodate high levels of deformation and stretchability in addition to high energy and power density, light weight, miniaturization in size, safety qualification, and other significant characteristics. Utilizing carbon nanotubes (CNTs) for various energy storage applications such as electrodes in lithium ion batteries and supercapacitors, are under close scrutiny because of the promising electrochemical performance in addition to their extraordinary tensile strength and flexibility, ultrahigh surface area, and excellent thermal and electrical conductivity. Recently, there has been growing interest in investigating CNT macro-films with large-scale organized nanostructures of desired shape and form and unique and enhanced properties: integrity and stability to realize the scaled-up energy storage devices. In this perspective, research efforts in assembling 2-D CNT macro-films using a chemical vapor deposition method and their applications for different energy storage devices including stretchable supercapacitors, supercapacitors working under extreme conditions such as high temperature and high pressure, and lithium–ion batteries are discussed. In details, this paper provides an original overview involving the effect of compressive stress on the electrochemical behavior of flexible supercapacitors assembled with CNT macro-film electrodes and electrolytes with different anions and cations; the demonstration of the dynamic and galvanic stability of stretchable supercapacitor using buckled CNT macro-films by an in situ dynamic electrochemical testing method; the understandings on the self-discharge mechanisms of CNT macrofilm-based supercapacitors from both electrode and electrolyte aspects; and the investigation of the electrochemical properties of the tandem structure of active materials (e.g. thin porous silicon film and CuO) with CNT macro-films acting as a flexible and adhesive layer between the active layers and current collectors for lithium–ion batteries. Future research on CNT macro-films-based lithium–sulfur batteries and lithium–air batteries is also discussed.

Dynamic and Galvanic Stability of Stretchable Supercapacitors

Stretchable electronics are emerging as a new technological advancement, since they can be reversibly stretched while maintaining functionality. To power stretchable electronics, rechargeable and stretchable energy storage devices become a necessity. Here, we demonstrate a facile and scalable fabrication of full stretchable supercapacitor, using buckled single-walled carbon nanotube macrofilms as the electrodes, an electrospun membrane of elastomeric polyurethane as the separator, and an organic electrolyte. We examine the electrochemical performance of the fully stretchable supercapacitors under dynamic stretching/releasing modes in different stretching strain rates, which reveal the true performance of the stretchable cells, compared to the conventional method of testing the cells under a statically stretched state. In addition, the self-discharge of the supercapacitor and the electrochemical behavior under bending mode are also examined. The stretchable supercapacitors show excellent cyclic stability under electrochemical charge/discharge during in situ dynamic stretching/releasing.

Strong carbon nanotube macro-films with retained deformability at fairly low temperatures

The tensile strength and elongation of carbon nanotube (CNT) macro-films with different thicknesses were measured from 150°C to −50°C. The microstructural deformation of the CNT macro-films during stretching was detected by scanning electron microscopy. The CNT bundles deposited nanoparticles in the macro-films entangled with one another and formed a highly porous network. Thus, the CNTs rearranged along the direction of the applied force. This unique rearrangement ability during stretching enabled the CNT macro-films to maintain their high plasticity even at the low temperature of −50°C. The tensile strength of the CNT macro-films also monotonically increased with decreased temperature. The fabricated CNT macro-films with special low-temperature mechanical properties have potential applications in low-temperature engineering and other related fields.

Purification of double-walled carbon nanotube macro-films

An effective NH4Cl-assisted method for purification of carbon nanotube (CNT) macro-films is reported. Compared to previous oxidation in acid, this method induces little destruction to the graphitic structure of CNTs, and more importantly, the morphology and integrity of the macroscopic film are maintained.

A statistical mechanics model of carbon nanotube macro-films

Carbon nanotube macro-films are two-dimensional films with micrometer thickness and centimeter by centimeter in-plane dimension. These carbon nanotube macroscopic assemblies have attracted significant attention from the material and mechanics communities recently because they can be easily handled and tailored to meet specific engineering needs. This paper reports the experimental methods on the preparation and characterization of single-walled carbon nanotube macro-films, and a statistical mechanics model on the deformation behavior of this material. This model provides a capability to optimize the synthesis process by comparing with the experiments.

Tandem Structure of Porous Silicon Film on Single-Walled Carbon Nanotube Macrofilms for Lithium-Ion Battery Applications

Development of materials and structures leading to high energy and power density lithium-ion batteries is a major challenge to the power needs of the electronic and automobile industries. Silicon is an attractive anode material being closely scrutinized for use in lithium-ion batteries but suffers from a poor cyclability and early capacity fading. In this work, we present a tandem structure of porous silicon film on single-walled carbon nanotube (SWNT) film to significantly improve the cycling stability of silicon as lithium-ion battery anode material. With this new structure configuration of the silicon films, a reversible specific capacity of 2221 mAh/g was retained after 40 charge-discharge cycles at 0.1 C rate, which is 3.6 times that of silicon film on a regular copper substrate and more than 11 times that of the SWNT film. The facile method is efficient and effective in improving specific capacity and stability of silicon anode lithium-ion batteries and will provide a powerful means for the development of lithium-ion batteries.

Preparation of Large Area Double-walled Carbon Nanotube Macro-films with Self-cleaning Properties

Double-walled carbon nanotube (DWCNT) macro-films with large areas, excellent flexibility and superhydrophobicity are reported. The area of the macro-film is larger than 30 cm × 15 cm, and this large film can be bended, or folded without any damage, and even can be tailored freely. After a simple modification of perfluoroalkysilane, the surface of the macro-film shows excellent superhydrophobicity with a water contact angle of 165.7±2 deg. and sliding angle lower than 3 deg., the prepared superhydrophobic films showing excellent antifouling, self-cleaning and water-repellent functions. The topographic roughness and perfluoroalkysilane modification are found to contribute to the observed superhydrophobicity. Considering the outstanding electronic, chemical and mechanical properties of DWCNTs, it is expected that this multifunctional DWCNT macro-film has potential applications in many fields.

Direct fabrication of single-walled carbon nanotube macro-films on flexible substrates

We employed a floating chemical vapor deposition technique and applied a liquid (solution)-free precursor system for the fabrication of single-walled carbon nanotube macro-films on various flexible substrates from metallic foils to polymer films.