Few-walled Carbon Nanotubes Research Articles

(Invited) Collective Radial Breathing Modes in Homogeneous Nanotube Bundles

Carbon nanotubes (CNTs) exist in many atomic structures typically grow as mixtures of of many chiralities with a vast variety of properties. Identical CNTs that are arranged into two-dimensional hexagonal lattices, their vibrational properties have been predicted to change with additional low-frequency modes appearing in the Raman spectrum. [1] Up to now, the experimental study of collective vibrations has been limited by a lack of pure homogeneous chirality bundles. We overcome this challenge by employing a self-coil mechanism of a very long CNT that loop into itself during the growth process resulting in a tightly packed hexagonal stack [2]. This lattice is perfectly homogeneous in terms of diameter, chiral twist, and even handedness of the tube. By characterizing and comparing the physical properties of the coil with respect to its tails, the bundling effects are clearly visible. We report on two breathing-like modes for quasi-infinite bundles, compared to the single radial breathing mode characteristic for isolated tubes. The exciton-phonon coupling in these modes is probed with resonant Raman spectroscopy, revealing the same resonance energy for both breathing-like peaks. Additionally, we study the dependence of vibrational coupling on the tube diameter by analysing different tube’s diameter coils and other bundling geometries. Our experimental findings align well with previously reported theoretical studies, demonstrating a 1/d scaling for all modes, as well as confirming the relative shift of the modes dependent on intertube interaction. These vibrations provide insight into the role of intertube lattice dynamics in two-dimensional THz-range phononic crystals.[1] Popov, V. N.; Henrard, L. Evidence for the existence of two breathinglike phonon modes in infinite bundles of single-walled carbon nanotubes. Phys. Rev. B 2001, 63, 233407[2] Nakar, D.; Gordeev, G.; Machado, L. D.; Popovitz-Biro, R.; Rechav, K.; Oliveira, E. F.; Kusch, P.; Jorio, A.; Galvao, D. S.; Reich, S.; others Few-wall Carbon Nanotube Coils. Nano Letters 2019, 20, 953–962.

Methodology for fast testing of carbon-based nanostructured 3D electrodes in vanadium redox flow battery

Progress in material chemistry is manifested daily by the variety of prepared functional materials, often with nanodimensional structuring. The electrodes for vanadium redox flow batteries have been shown to benefit from incorporating nanostructured materials such as carbon nanotubes. However, the methods of such incorporation are far from optimal, relying mainly on physical deposition or insertion into a binder. Here, we describe a technique for integrating carbon-based rod-like nanomaterials into a vanadium redox flow battery and a methodology for fast nanomaterial performance testing. The technique is based on creating a fixed nanomaterial bed sandwiched between two graphite felt electrodes, forming a 3D flow-through electrode in the battery. Performing various positive and negative control experiments, we show the beneficial effect of a nanostructured bed on the primary battery characteristics obtained from short-term electrochemical experiments. We characterize carbon nanotubes exhibiting promising electrochemical behavior in vanadium electrolytes, as observed in our previous study. The load curves obtained from charge-discharge steps at various current densities and electrolyte flow rates revealed considerable differences in the performance of the tested materials, with few-walled carbon nanotubes reaching unsurpassable characteristics. At room temperature, with 50 %-SOC-working solutions and the highest tested linear velocity of 14.6 cm/min, the evaluated power density for this material reached values above 500 mW/cm2. For comparison, thermally treated graphite felt, used as a benchmark material, provided a power density of around 300 mW/cm2 under identical conditions. Although developed for vanadium redox flow batteries, the method enables testing tube-like and rod-like (nano-)materials for flow electrochemical systems.

Inter-Shell Sliding in Individual Few-Walled Carbon Nanotubes for Flexible Electronics.

Few-walled carbon nanotube (FWCNT) is composed of a few coaxial shells of CNTs with different diameters. The shells in one tube can slide relatively to each other under external forces, potentially leading to regulated electrical properties, which are never explored due to experimental difficulties. In this work, the electromechanical response induced by inter-shell sliding of individual CNTs is studied and revealed the linear electrical current variation for the first time. Based on centimeter-long FWCNTs grown through chemical vapor deposition, controllable and reversible inter-shell sliding is realized while simultaneously recording the electrical current. Reversible and linear current variation with inter-shell sliding is observed, which is consistent with the proposed inter-shell tunneling model. Further, a silk fibroin-assisted transfer technique is developed for long CNTs and realized the fabrication of FWCNT-based flexible devices. Tensile stress can be applied on the FWCNTs@silk film encapsulated in elastic silicone to induce inter-shell sliding and thus controls electrical current, which is demonstrated to serve as a new human-machine interface with high reliability. Besides, it is foreseen that the electromechanical behaviors induced by inter-layer sliding in 1D nanotubes may also be extended to 2D layered materials, shedding new light on the fabrication of novel electronics.

Synthesis and characterization of P3HT:ZnO-FWCNTs for possible application in organic solar cells

Zinc oxide (ZnO) and few-walled carbon nanotubes (FWCNTs) mixed in poly(3-hexylthiophene-2,5-diyl) (P3HT) were prepared for application in organic solar cells (OSCs) as photoactive materials. ZnO was synthesized by microwave-assisted sol-gel method. Improved properties were found for the nanocomposite with 3 wt% of FWCNTs concentration. XRD revealed the hexagonal wurtzite structure of ZnO and the nanocomposites (ZnO-FWCNTs) showed both hexagonal wurtzite and carbon structure. UV/Vis/NIR and PL studies revealed a relatively higher photon absorption efficiency and emission intensity from the ZnO-3% FWCNTs. PL intensity of P3HT was quenched from the sample P3HT:ZnO-3% FWCNTs with the ratio of 1:1, indicating charge transfer phenomena between the electron donor (P3HT) and an acceptor (ZnO-FWCNTs) materials. FESEM showed well-mixed ZnO nanorods with P3HT. Current-voltage measurements indicated an improved electrical conductivity for P3HT:ZnO-3% FWCNTs (ratio 1:1). The obtained results suggest that this sample can potentially improve the photoelectrical conversion efficiency of the OSCs.

Enhanced the Stability and Storage Capability of Sulfide-Based Material With the Incorporation of Carbon Nanotube for High-Performance Supercapattery Device

Abstract Supercapattery is a recently developed energy storage device that includes the properties of a supercapacitor and a rechargeable battery. A hydrothermal method is used to synthesize the sulfide-based materials. The structural morphology, elemental composition, and electrochemical properties are measured using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and potentiostat system. The specific capacitance is enhanced up to 1964.2 F/g by making the composite with carbon nanotubes (CNTs), which is higher than the reference sample (MnS). In the case of a real device, the obtained value of specific capacity in manganese sulfide/CNTs/activated carbon is 240 C/g which is much improved compared to the previously reported values. In a supercapattery device, an excellent energy density of 53.3 Wh/Kg and a high power density of 7995 W/kg are obtained. The stability of the device is measured up to 1000 cycles and achieved the specific capacity retention of 86% with columbic efficiency of 97%. Electrochemical impedance spectroscopy (EIS) and Brunauer–Emmett–Teller (Lee et al., 2012, Self-standing Positive Electrodes of Oxidized few-Walled Carbon Nanotubes for Light-Weight and High-Power Lithium Batteries,” Energy Environ. Sci., 5(1), pp. 5437–5444) measurements confirm the improvement in surface area and electrochemical properties. Our results show that a 50/50 weight ratio of manganese sulfide and CNTs are more suitable and provide opportunities to design high-performance energy storage devices.

Micro and macroscopic structure evolution of few-walled carbon nanotube bundled network by high temperature anneal

High temperature anneal is of importance to create nanocarbon-based materials with excellent functions and performances. However, a comprehensive understanding on annealed nanocarbon assembly structures has been challenging. We successfully propose the micro and macroscopic structural analysis of 0.8–3.4 nm diameter few-walled carbon nanotube (CNT) bundled network by a multifaceted characterization, which were annealed over 1200–3000 °C in the form of a film as the case study. Up to 1800 °C carbonaceous impurities were removed to secure nanospace among nanotubes, i.e. interstitial channels important to design multiple functions. Beyond 1900 °C nanoscale graphitic particles were generated on the nanotube bundles, then grown to be micro-meter scale toward 3000 °C. Parallel to the particle growth, small diameter (<1.2 nm) nanotubes became undetected at 2200–2400 °C with a decrease in available interstitial channels, finally resulting in the nontubular, graphitized network structures at 2600–3000 °C. The anneal at 1200–1800 °C can afford the high purity CNT bundled network structures, and the higher temperature anneal led to the high crystallinity graphitized network structures. To understand the structural evolution, 14 different analytical methods were employed, and two-dimensional correlation analysis from the collected data revealed the synchronous and asynchronous structural parameters with the annealing temperature. Thus, we found that the structural changes occurred in 3 stages of 1200–1800 °C, 1900–2400 °C, and 2600–3000 °C. On the other hand, the electrical conductivity gradually decreased due to the removed carbonaceous impurities and the structure changes. Our findings can be an asset for carbon material science and pave a way toward nanocarbon applications with the films, fibers, and composites.

Highly surface-conformable thermoelectric patches for efficient thermal contact with arbitrary substrates

Organic thermoelectric (TE) materials are attractive for application as the main or auxiliary power sources of portable and wearable electronic devices. Although utilizing waste heat from practical heat sources (including the human body) remains challenging, this can be solved by developing surface-conformable and body-attachable TE materials. This study introduces a method for preparing multifunctional TE patches to facilitate efficient thermal contact formation between TE patches and various heat sources with flat, curved, wavy, wrinkled, or microstructured surfaces and different textures. The TE patches are prepared using a mixed solution comprising few-walled carbon nanotubes, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate), and a commercial gel polymer blend to form freestanding hydrogel nanocomposite films. Under optimized conditions, the composite films exhibit good mechanical (bending and healing) and TE properties and excellent environmental long-term stability. Because the films can form superior thermal contact with arbitrary surfaces, energy can be harvested more efficiently using the conformable TE patches than using the nonconformable patches, suggesting that the potential application range of organic TE materials for future self-powered wearable electronics is not limited to energy harvesting but can be extended to precise temperature sensing.

(Invited) Production and Functionalization of Carbon Nanotubes for Electrochemical Energy Storage Devices

Self-supporting, sponge-like paper of carbon nanotubes (CNTs) can be a new platform for high energy/power density batteries. Presently, battery electrodes are built on metallic foils having only two faces and large mass with the aid of polymeric binders and conductive fillers. CNT paper can replace all these components. Furthermore, it captures nanomaterials at high loading, activates insulative materials, and moderates volumetric change of active materials.We have developed semi-continuous fluidized bed chemical vapor deposition method [1], which yields submillimeter-long few-wall CNTs with carbon purity >99 wt% and metal impurity <0.1 wt% [2]. By capturing capacitive particles (99 wt%) with CNTs (1 wt%), a lithium ion full cell with graphite-CNT anode and LiCoO2-CNT cathode is demonstrated (Figure 1b) [3]. This platform is also effective to create electrodes of the emerging active materials such as Si anode [4] and S cathode [5] with practically high gravimetric, areal, and volumetric loadings, and realized Li x Si-S and Li-Li2S x full cells [6,7]. In addition, by combining with the insulative sponge of boron nitride nanotubes (BNNTs), the graphite-CNT|BNNT| LiCoO2-CNT full cell with high thermal stability was developed [8].[1] D.Y. Kim, et al., Carbon 49, 1972 (2011).[2] Z. Chen, et al., Carbon 80, 339 (2014).[3] K. Hasegawa and S. Noda, J. Power Sources 321, 155 (2016).[4] T. Kowase, et al., J. Power Sources 363, 450 (2017).[5] K. Hori, et al., J. Phys. Chem. C 123, 3951 (2019).[6] K. Hori, et al., Carbon 161, 612-621 (2020).[7] Y. Yoshie, et al., Carbon 182, 32-41 (2021).[8] K. Kaneko, et al., Carbon 167, 596-600 (2020).Figure 1. (a) Semi-continuous production of submillimeter-long few-wall CNTs by fluidized bed [1]. (b) Lithium ion full cell made of graphite-CNT anode and LiCoO2-CNT cathode [3]. Figure 1

Tuning carbon nanotube-based buckypaper properties by incorporating different cellulose nanofibrils for redox supercapacitor electrodes

In recent years, supercapacitors (SCs) that employ redox electrolytes have stood out as a simple technology that allows maximizing the energy density of this class of devices. However, there is a growing demand for integrable devices, and few studies focus on obtaining moldable, thin, and flexible electrode materials with a high capacity to electrosorb the redox additives from the electrolyte. In this work, we report the preparation of buckypapers (BPs) composed of few-walled carbon nanotubes (FWCNT) and different cellulose nanofibrils (CNF) for application as flexible and foldable redox SC electrodes. Thus, we aim to demonstrate and discuss how different CNFs affect the hydrophilicity, mechanical strength, electrical conductivity, textural properties, and electrochemical performance of BPs immersed in an electrolyte containing the [Fe(CN)₆]4−/[Fe(CN)₆]3− redox couple. For this, three different sources of cellulose were used for the preparation of CNFs with dimensions less than 100 nm in diameter and lengths in the order of hundreds of micrometers: Eucalyptus sp, Pinus sp, and Bambusa vulgaris. Our results reveal that more hydrophobic CNFs (mainly from Bambusa vulgaris) favor the formation of stronger interactions in networks with FWCNTs, promoting the highest increases in maximum strain (215%), and the highest specific capacitances (167.6 F g−1 at 4.42 mA cm−2). Finally, this work demonstrates that CNFs can be used not only as ligands but as active components that allow optimizing several properties of BPs and their performance as redox SC electrodes.

Few-walled carbon nanotubes derived from shoe waste plastics: Effect of feedstock composition on synthesis, properties and application as CO2 reduction electrodes

This work investigates the chemical recycling of shoe waste plastics, i.e. polyurethane (PU) and ethylene-vinyl acetate (EVA) using a pyrolysis-chemical vapor deposition process over Fe/MgO catalyst. Results suggested PU facilitated highly selective production of few-walled CNTs with small diameters and narrow size distribution while EVA tended to yield multi-walled CNTs. The synergistic interactions between pyrolysis gases components from PU and EVA allowed facile tailoring of CNT size distribution by using either sorted PU and EVA or mixture (EVA/PU) in appropriate ratios. CNTs derived from pure PU or EVA/PU were more suitable in designing effective electrocatalysts for CO2 reduction with Faradaic efficiency of 85–95% and CO current density of >9 mA cm−2. This was because the presence of few-walled CNTs could enhance electrical conductivity and specific surface area without compromising the loading of active materials.

Converting polyolefin plastics into few-walled carbon nanotubes via a tandem catalytic process: Importance of gas composition and system configuration

Polyolefins such as polyethylene (PE) and polypropylene (PP) are abundant components of plastic waste. Chemical recycling of PE and PP via pyrolysis followed by chemical vapor deposition typically results in the growth of multi-walled carbon nanotubes (CNTs). Here, a tandem catalytic system for the growth of few-walled CNTs is reported. The successful synthesis of few-walled CNTs in the system relies on the catalytic processing of pyrolysis gas from plastics into intermediate gas mixtures containing mainly paraffins and hydrogen (700 °C, catalyst: 40 wt% Co, 10 wt% Mo and 50 wt% MgO). Under appropriate conditions (1000 °C, catalyst: Co 3 wt%, Mo 2 wt% and MgO 95 wt%, synthesis time: 20 min), the obtained intermediate gas mixture was selectively converted into few-walled CNTs with > 95% CNTs having small outer diameters of 1–7 nm, containing CNTs with as little as three walls and having distinct radial breathing mode in Raman spectra at wave lengths 100–400 cm−1. The proposed synthesis process opens new opportunities for production of high value few-walled CNTs from plastic waste.

Highly flat and highly homogeneous carbon paper with ultra-thin thickness for high-performance proton exchange membrane fuel cell (PEMFC)

Gas diffusion layer is one of the most important components of fuel cell, which supports the catalytic layer, collects the current and facilitates mass transfer. However, current carbon paper is mainly composed of long carbon fibers (CF), which brings drawbacks including rough surface, poor body homogeneity, excessive thickness, and preparation difficulty, etc. In this research, we invent a combination method to produce a highly flat, highly homogeneous, ultra-thin and high-performance carbon paper for proton exchange membrane fuel cell (PEMFC). The method combines the advantages of two materials, i.e. few-walled carbon nanotube (FWCNT) with high flatness and short CF with high porosity. And the combination method only contains three steps, material dispersion, carbon paper formation and heat treatment. The highest temperature for the heat treatment process is only 350 °C, which is much lower than the traditional 2000 °C. Due to the small size and fine distribution of FWCNT and CF, the new carbon paper exhibits highly flat (<6.4 μm in average), highly homogeneous (<3.6 μm in average), ultra-thin (<60 μm) properties, and high-performance in PEMFC. Therefore, this work shows that the optimized combination of several materials with outstanding properties could be used to prepare high performance carbon paper for PEMFC. • Preparation method of ultra-thin, highly flat and highly uniform carbon paper. • Contribution of FWCNT and short CF to thin, flat and uniform carbon paper surface. • Ohmic impedance and charge mass transfer impedance are the main factors. • Critical area in MEA are the two interfaces among the CL, GDL, and Nafion membrane.

Micro and Macroscopic Structure Evolution of Few-Walled Carbon Nanotube Bundled Network by High Temperature Anneal

Micro and Macroscopic Structure Evolution of Few-Walled Carbon Nanotube Bundled Network by High Temperature Anneal

Nucleation of carbon-sulfur phases by manipulation of vertically-aligned mm-long films of iron-filled few-wall/multiwall carbon nanotubes

• We report a novel Cl- & S-assisted fabrication of vertically-aligned mm-long films of few-walls carbon nanotubes (CNTs). • The employed quantity of sulfur was found to yield either few wall CNTs (FWCNTs) or multiwall CNTs (MWCNTs) in presence of 0.4 mg or 1.2 mg. • Structural manipulation was sought through annealing at T∼ 150 °C, 300 °C and 600 °C in presence of high concentration of sulfur. • We demonstrate the appearance of dominant Raman bands indicative of carbon-sulfur bonding (shifts of 1250 cm −1 and 1450 cm −1 ) at T∼ 150 °C, 300 °C. • The effects of the doping process were investigated through T-dependent EPR. We report a novel investigation of the effects of sulfur-precursor concentration on the morphological, structural and magnetic properties of vertically aligned mm-long films of carbon nanotubes (CNTs) filled with Fe 3 C nanowires. Fabrication was carried out by sublimation and pyrolysis of ferrocene/sulfur mixtures in the presence of 0.65 ml of dichlorobenzene within a custom designed chemical vapour deposition (CVD) reactor, under an Ar flow of 10-100 ml/min. The employed quantity of sulfur was found to have an important impact on the structural properties of the as grown CNTs, yielding either few wall CNTs (FWCNTs) or multiwall CNTs (MWCNTs) in presence of 0.4 mg or 1.2 mg of sulfur (category 1,2). Appearance of RBM (radial breathing modes) bands with variable intensities, was demonstrated in category-1 samples by both point and mapping Raman spectroscopy. Further, an additional broad band indicative of a chlorine/sulfur-induced amorphization of the CNT-walls was detected. Structural manipulation of category-1 and-2 samples was sought through annealing, in an attempt to create carbon-sulfur phases. The latter system has been indeed recently identified as a possible superconductor, under certain conditions of doping. Our findings highlight two different regimes of carbon-sulfur manipulation of the CNT-layers which involve 1) the nucleation of covalent carbon-sulfur phases at T∼150 °C -300 °C, with appearance of Raman bands at 1250 cm −1 and 1450 cm −1 and 2) an enhancement of the CNT-defectiveness (D and D’ bands) at T∼600 °C.

Controllable pore structures of pure and sub-millimeter-long carbon nanotubes

We report the controllable pore structures of pure (>99.5 wt%) and sub-millimeter-long single-walled and few-walled (triple-walled on average) carbon nanotubes (SWCNTs and FWCNTs, respectively) synthesized via fluidized-bed chemical vapor deposition. The pore structures and adsorption properties of the CNTs were characterized using N2 adsorption analysis at 77 K. A significant advantage of the synthesized vertically-aligned SWCNTs (diameter range: 2–4 nm) and FWCNTs (diameter range: 4–8 nm) arrays, having small bundle structures, is that the guest molecules can easily access the external surfaces of the CNTs, leading to high specific surface areas (SSAs; 903 and 337 m2 g−1, respectively) and pore volumes (2.56 and 2.05 mL g−1, respectively). Interestingly, following sonication, the SSAs of the SWCNTs and FWCNTs increased by 36% and 41%, respectively. Additionally, after mixed acid (HNO3/H2SO4) treatment, the SSAs of the SWCNTs and FWCNTs increased by 34% and 120%, respectively, which are attributed to the corresponding increases in the micropore and mesopore SSAs. These results suggest that CNT networks with controllable pore structures can be fabricated by altering the diameter distribution and alignment degree of the CNTs, thus highlighting the potential of our approach to develop cost-effective CNT-based structures for applications such as high-performance energy storage materials.

A Meta-Analysis of Conductive and Strong Carbon Nanotube Materials.

A study of 1304 data points collated over 266 papers statistically evaluates the relationships between carbon nanotube (CNT) material characteristics, including: electrical, mechanical, and thermal properties; ampacity; density; purity; microstructure alignment; molecular dimensions and graphitic perfection; and doping. Compared to conductive polymers and graphitic intercalation compounds, which have exceeded the electrical conductivity of copper, CNT materials are currently one-sixth of copper's conductivity, mechanically on-par with synthetic or carbon fibers, and exceed all the other materials in terms of a multifunctional metric. Doped, aligned few-wall CNTs (FWCNTs) are the most superior CNT category; from this, the acid-spun fiber subset are the most conductive, and the subset of fibers directly spun from floating catalyst chemical vapor deposition are strongest on a weight basis. The thermal conductivity of multiwall CNT material rivals that of FWCNT materials. Ampacity follows a diameter-dependent power-law from nanometer to millimeter scales. Undoped, aligned FWCNT material reaches the intrinsic conductivity of CNT bundles and single-crystal graphite, illustrating an intrinsic limit requiring doping for copper-level conductivities. Comparing an assembly of CNTs (forming mesoscopic bundles, then macroscopic material) to an assembly of graphene (forming single-crystal graphite crystallites, then carbon fiber), the ≈1 µm room-temperature, phonon-limited mean-free-path shared between graphene, metallic CNTs, and activated semiconducting CNTs is highlighted, deemphasizing all metallic helicities for CNT power transmission applications.

SnO2-MoO3 nanoparticles anchored in carbon nanotubes as a large-capacity, high-rate, and long-lifetime anode for lithium-ion batteries

SnO2-MoO3 hybrid nanoparticles are anchored in a few-walled carbon nanotube (CNT) network to synthesize SnO2-MoO3-CNT nanocomposite by hydrothermal and ball grinding methods. The CNTs can alleviate the volume expansion of SnO2, improve conductivity and shorten the transmission paths of the electrons and Li+. The SnO2-MoO3-CNT composite has a high initial coulombic efficiency of 80.9% and shows a large invertible capacity of 1372.2 mAhg−1 after 280 cycles at 0.2 Ag-1 and the coulomb efficiency holds more than 98.0% after the second cycle, high-rate property of 743.6 mAhg−1 at 5.0 Ag-1 and long-term cycling capacity of 886.3 mAhg−1 at 1.0 Ag-1 after 950 cycles. Because of its outstanding properties, ternary SnO2-MoO3-CNT nanocomposite is a confident anode material for lithium-ion batteries.

High-energy-density Li–S battery with positive electrode of lithium polysulfides held by carbon nanotube sponge

Lithium-sulfur battery suffers from the low utilization of sulfur and the high electrolyte/sulfur (E/S) ratio that decrease the cell-based performance. Lithium polysulfides (Li2Sx)-dissolved electrolyte, so called catholyte, enables high utilization of sulfur, but the cell inherently has high E/S ratio due to the limited solubility of Li2Sx. Herein, a composite electrode of Li2Sx (x = 4, 6, 8) and sub-millimeter-long few-wall carbon nanotube (CNT) is proposed. The CNT forms self-supporting sponge-like paper and works as a three-dimensional current collector, in which the Li2Sx is deposited by solution casting and drying. The Li2S6-CNT electrode realizes high specific capacity (1249 mAh gsulfur−1) under a lean electrolyte condition of E/S = 4 μL mgsulfur−1, which is much better than the S8-CNT electrode (233 mAh gsulfur−1). After full charge and conversion of Li2Sx to S, the Li2Sx-CNT electrode maintains its high capacity of 1100 mAh gsulfur−1. The full cell with the Li2S6-CNT and the Li thin foil electrodes realizes 400–500 Wh kgcell−1 for E/S = 4.0 at the 2nd and 3rd discharge and 300 Wh kgcell−1 for E/S = 5.8 at the 97th discharge, based on the total mass of the interior of a cell (electrodes, separator, and electrolyte). Holding solvated Li2Sx by the CNT sponge is the key for the high energy density.

SnO2–ZrO2 nanoparticles embedded in carbon nanotubes as a large capacity, high rate and long lifetime anode for lithium-ion batteries

SnO2–ZrO2 composite nanoparticles were embedded in the few-walled carbon nanotubes (FWCNTs) network to synthesise a ternary SnO2–ZrO2-CNT nanocomposite by the hydrothermal and ball milling methods. The SnO2–ZrO2 composite was uniformly dispersed in the CNT matrix. The CNTs in the composite alleviated the volume expansion during cycling, improved conductivity, and shortened the transmission path of electrons and Li+. Therefore, the SnO2–ZrO2-CNT composite showed high reversible capacity of 1072.2 mAhg−1 after 200 cycles at 0.2 Ag-1 with high initial coulomb efficiency of 77.9% and >98.8% in the following cycles, high-rate capacity of 653.6 mAhg−1 at 5.0 Ag-1, and long-term capacity of 610.7 mAhg−1 at 5.0 Ag-1 after 1000 cycles. Because of its outstanding properties, the SnO2–ZrO2-CNT nanocomposite is a promising anode material for next-generation lithium-ion batteries.

Intense Raman D Band without Disorder in Flattened Carbon Nanotubes.

Above a critical diameter, single- or few-walled carbon nanotubes spontaneously collapse as flattened carbon nanotubes. Raman spectra of isolated flattened and cylindrical carbon nanotubes have been recorded. The collapse provokes an intense and narrow D band, despite the absence of any lattice disorder. The curvature change near the edge cavities activates a D band, despite framework continuity. Theoretical calculations based on Placzek approximation fully corroborate this experimental finding. Usually used as a tool to quantify defect density in graphenic structures, the D band cannot be used as such in the presence of a graphene fold. This conclusion should serve as a basis to revisit materials comprising structural distortion where poor carbon organization was concluded on a Raman basis. Our finding also emphasizes the different visions of a defect between chemists and physicists, a possible source of confusion for researchers working in nanotechnologies.