Disordered Carbon Layer Research Articles

Integration of Cointercalation and Adsorption Enabling Superior Rate Performance of Carbon Anodes for Symmetric Sodium-Ion Capacitors.

Carbon materials have been the most common anodes for sodium-ion storage. However, it is well-known that most carbon materials cannot obtain a satisfactory rate performance because of the sluggish kinetics of large-sized sodium-ion intercalation in ordered carbon layers. Here, we propose an integration of co-intercalation and adsorption instead of conventional simplex-intercalation and adsorption to promote the rate capability of sodium-ion storage in carbon materials. The experiment was demonstrated by using a typical carbon material, reduced graphite oxide (RGO400) in an ether-solvent electrolyte. The ordered and disordered carbon layers efficiently store solvated sodium ions and simplex sodium ions, which endows RGO400 with enhanced reversible capacity (403 mA h g-1 at 50 mA g-1 after 100 cycles) and superior rate performance (166 mA h g-1 at 20 A g-1). Furthermore, a symmetric sodium-ion capacitor was demonstrated by employing RGO400 as both the anode and cathode. It exhibits a high energy density of 48 W h g-1 at a very high power density of 10,896 W kg-1. This work updates the sodium-ion storage mechanism and provides a rational strategy to realize high rate capability for carbon electrode materials.

Synergetic optimization of p-type Ba2+ substitution and carbon nanotubes enwrapping in Na3V2(PO4)3: A superior cathode with high electrochemical and safety performance for half and full cells

Na3V2(PO4)3 (NVP) has been deemed as a promising cathode because of high capacity and good stability. Nevertheless, poor intrinsic conductivity seriously limits its further application. Herein, partial Ba2+ substitution on V3+ site is introduced to modify NVP in terms of increasing cell volume due to larger ionic radius of Ba2+ and generating beneficial hole carriers derived from p-type doping. The expanded crystal channels efficiently facilitate the Na + migration and the hole carriers are beneficial for transfer charge to improve electronic conductivity. Ba2+ doping further enhances the structural stability due to the pillar effect, which has been proved by DSC measurement. The increase of exothermic peak temperature and decrease of heat release rate demonstrates the excellent thermal stability of NVBa0.07P@CNTs. Moreover, disordered carbon layer and enwrapped CNTs construct an effective network to provide abundant routes for electronic transportation. Notably, the optimized NVBa0.07P@CNTs delivers superior electrochemical performance in both half and full cells. It releases a capacity of 117.23 mA h g−1 at 0.1C and submits a capacity of 101.99 mA h g−1 with retention of 80% at 15 C over 2000 cycles. Even at 50 C, it still delivers a high value of 78.33 mA h g−1.

Interlayer and doping engineering in partially graphitic hollow carbon nanospheres for fast sodium and potassium storage

Constructing anodes with fast ions/electrons transfer paths is an effective strategy to achieve high-performance sodium ion batteries (SIBs)/potassium ion batteries (PIBs). Amorphous carbon is a promising candidate anode for SIBs/PIBs owing to its disordered carbon layers, abundant defects/pores, and low-cost resources. However, the larger radius of Na+/K+ leading to depressed kinetics and poor cycling performance, impeding their further applications. Herein, we propose an efficient strategy to construct of nitrogen, sulfur co-doped hollow carbon nanospheres (NS-HCS) involving an in situ growth of polydopamine on nano-Ni(OH)2 template with subsequent sulfur doping process. During the formation process, the produced Ni nanospheres play as the hard template and catalyst for the formation of hollow carbon nanosphere with partially graphite microcrystalline structure, while the sulfur doping process can enlarge the interlayer space and create more defects on the surface of carbon nanospheres, thus synchronous improve the Na+/K+ insertion and adsorption ability in NS-HCS. With the synergistic control of the enlarged interlayer spacing, high content of pyridinic N/pyrrolic N and graphitization, a hybrid storage mechanism facilitates the transport kinetics and endows the NS-HCS electrode with high capacities and good cycling stability in SIBs and PIB. Benefit from the multiple effects, NS-HCS exhibits the improved capacity of 274.8 mAh/g at 0.1 A/g and excellent cycling stability of 149.5 mAh/g after 5000 cycles at 2.5A/g in SIBs, as well as good potassium ion storage behavior with a high capacity retention of 76.5% after 700 cycles at 1.0 A/g, demonstrating the potential applications of NS-HCS for high-performance SIBs and PIBs

Facile synthesis of Co9S8@NC anode with enhanced sodium storage and long cycling life

Transition metal sulfides (TMSs) are presently under extensive research and have been regarded as the prospective anode candidates for sodium ion batteries (SIBs). However, the poor intrinsic electrical conductivity and huge volume expansion of metal sulfides electrodes during the discharge-charge process eventually cause pulverization of active materials and quick capacity decay, which severely limit their further practical application. In this study, ultrafine Co9S8 nanoparticles embedded in N-doped carbon layer (Co9S8@NC) were facilely synthesized via a simple one-step solid phase calcination method with glucose as the carbon source and thiourea served as N, S-containing precursor. The Co9S8@NC hybrid with small nanoparticle size could aid in the quick penetration of the electrolyte and shorten the pathway of Na ions diffusion; Meanwhile, the N-doped disordered carbon layer could maintain structural integrity and favor the electron transport of the nanocomposite during the electrochemical reaction. The Co9S8@NC composite is firstly investigated as anode for SIBs. They exhibit a satisfied discharge/charge specific capacity of 285.3/276.3 mAh g-1 after 160 cycles at 170 mA g−1, and its discharge/charge specific capacity is capable to maintain 160.8/158.5 mAh g−1 even after 1000 cycles at 1000 mA g−1. Further kinetics analyses based on CV demonstrate that the partial pseudocapacitive behaviors partially accounts for the remarkable Na storage performances.

Revealing Molecular Mechanisms in Hierarchical Nanoporous Carbon via Nuclear Magnetic Resonance

Author(s): Mao, H; Tang, J; Xu, J; Peng, Y; Chen, J; Wu, B; Jiang, Y; Hou, K; Chen, S; Wang, J; Lee, HR; Halat, DM; Zhang, B; Chen, W; Plantz, AZ; Lu, Z; Cui, Y; Reimer, JA | Abstract: Hierarchical nanoporous carbons combining pore sizes of different length scales are highly important for separation processes. However, critical questions remain regarding the hierarchical structure regulation and the molecular mechanisms of gaseous adsorbate uptake and interactions within the hierarchical nanoporous carbons. These materials present characterization challenges in that there are no experimental techniques that can elucidate the molecular mechanisms of the organic compounds and CO within the materials. We deployed multidimensional solid-state nuclear magnetic resonance (NMR) to generate maps of guest-framework interactions as a function of adsorbate concentrations and adsorption times. The NMR spectra provide insight toward the design of effective hierarchical pore structures. Our materials show a high volatile organic compounds/CO physisorption capacity, which reveals promising application to carbon-capture strategies to mitigate global warming. 2 2

Ultrahigh “Relative Energy Density” and Mass Loading of Carbon Cloth Anodes for K-Ion Batteries

Mass loading and potential plateau are the two most important issues of potassium (K)-ion batteries (KIBs), but they have long been ignored in previous studies. Herein, we report a simple and scala...

Impact of Microstructure on the Electrochemical Performance of Round-Shaped Pitch-Based Graphite Fibers

In this study, three kinds of round-shaped pitch-based graphite fiber with different microstructural features (crystallinity and carbon layer orientation) were fabricated by melt-spinning, preoxidation, carbonization and graphitization. The morphology, crystalline size and carbon layer orientation of carbon fibers from different pitch precursors and spinning rates were characterized through X-ray diffraction, scanning electron microscopy and transmission electron analyses. The correlation of the electrochemical performance and microstructure of graphite fibers as anode materials for lithium-ion batteries was investigated. The results suggest that large-diameter anisotropic graphite fibers (L-AF3000) with a radial texture of the transverse section are more favorable for lithium intercalation storage. The discharge capacity of L-AF3000 is 319.1 mAh∙g−1 at 0.1 C (current density). Nevertheless, the capacity drops to 209.9 mAh∙g−1 at a high current density of 1 C, and the capacity retention is only 82.2% over 100 cycles at 0.1 C. Small-diameter anisotropic graphite fibers (S-AF3000) with a spiral-shaped wrinkle texture of the transverse section possess discharge capacities of 284.1 mAh∙g−1 at 0.1 C and 260.2 mAh∙g−1 at a high current density of 1 C. Meanwhile, the best capacity retention of the fibers is 101.6% over 100 cycles at 0.1 C. The results suggest that the disordered carbon layers in S-AF3000 can retain the structural integrity of fibers as anode material for lithium-ion batteries and thus obtain excellent cycle stability. In addition, larger crystalline sizes of fibers correspond to higher discharge capacity, and a smaller diameter is beneficial to the fast insertion and extraction of lithium-ion in fibers.

Promoted electro-responsive performances in an interface-confined oxidized niobium carbide MXene

The transition metal carbides and nitrides (called MXenes), have garnered great attention due to their versatile surface chemistry and unique layered structure. The terminated functional groups of MXene are critical in developing intriguing properties to the increasing demand of intelligent control systems. This study demonstrates the synthesis of oxidized Nb2CTx MXene via two procedures, a hydrothermal process (h-Nb2O5/C) or CO2 calcination (c-Nb2O5/C). The obtained Nb2O5/C exhibits a hierarchical architecture with Nb2O5 nanoparticles decorated on the surface of disordered carbon layers. Attractively, the electrorheological (ER) performance of h-Nb2O5/C based ER fluid is superior to that of the c-Nb2O5/C based one. Combining the XPS, EDX and BET results, we speculate that the outstanding ER behavior is related to the following synergistic effects: large oil-accessible surface of the disordered carbon as well as high dielectric constant of the Nb2O5 nanoparticles. Notably, the h-Nb2O5/C based ER fluids possess a stable plateau region of shear stress throughout a wide range of shear rate, which is valuable for a host material of practical engineering applications.

Utilizing the full capacity of carbon black as anode for Na-ion batteries via solvent co-intercalation

Carbonaceous materials have long been considered promising anode materials for Na-ion batteries. However, the electrochemical performance of conventional carbon anodes is generally poor because the sodium ion storage solely relies on the disordered region of the carbon materials in a carbonate-based electrolyte. The solvent co-intercalation mechanism for Na ions has been recently reported in natural graphite anodes for Na-ion batteries with ether-based electrolytes, but their capacities are still unsatisfactory. We show here for the first time that by combining regular Na ion storage in the disordered carbon layer and solvent co-intercalation mechanism in the graphitized layer of a commercial N330 carbon black as an anode material for Na-ion batteries in ether-based electrolyte, the reversible capacity could be fully realized and doubled in magnitude. This unique sodium intercalation process resulted in a significantly improved electrochemical performance for the N330 electrode with an initial reversible capacity of 234 mAh·g–1 at 50 mA·g–1 and a superior rate capability of 105 mAh·g–1 at 3,200 mA·g–1. When cycled at 3,200 mA·g–1 over 2,000 cycles, the electrode still exhibited a highly reversible capacity of 72 mAh·g–1 with a negligible capacity loss per cycle (0.0167%). Additionally, surface-sensitive C K-edge X-ray absorption spectroscopy, with the assistance of electrochemical and physicochemical characterizations, helped in identifying the controlled formation and evolution of a thin and robust solid electrolyte interphase film. This film not only reduced the resistance for sodium ion diffusion, but also maintained the structural stability of the electrode for extended cycle reversibility. The superior electrochemical performance of N330 carbon black strongly demonstrated the potential of applying ether-based electrolytes for a wide range of carbon anodes apart from natural graphite.

Interface evolution in the platelet-like SiC@C and SiC@SiO2 monocrystal nanocapsules

Carbon-coated SiC@C nanocapsules (NCs) with a hexagonal platelet-like morphology were fabricated by a simple direct current (DC) arc-discharge plasma method. The SiC@C NCs were monocrystalline, 120–150 nm in size, and approximately 50 nm thick. The formation of the as-prepared SiC@C NCs included nucleation of truncated octahedral SiC seeds and subsequent anisotropic growth of the seeds into hexagonal nanoplatelets in a carbon-rich atmosphere. The disordered carbon layers on the SiC@C NCs were converted into SiO2 shells of SiC@SiO2 NCs by heat treatment at 650 °C in air, during which the shape and inherent characteristics of the crystalline SiC core were obtained. The interface evolution from carbon to SiO2 shells endowed the SiC@SiO2 NCs with enhanced photocatalytic activity due to the hydrophilic and transparent nature of the SiO2 shell, as well as to the photosensitive SiC nanocrystals. The band gap of the nanostructured SiC core was determined to be 2.70 eV. The SiC@SiO2 NCs degraded approximately 95% of methylene blue in 160 min under visible light irradiation.

Laser-induced phase separation of silicon carbide.

Understanding the phase separation mechanism of solid-state binary compounds induced by laser–material interaction is a challenge because of the complexity of the compound materials and short processing times. Here we present xenon chloride excimer laser-induced melt-mediated phase separation and surface reconstruction of single-crystal silicon carbide and study this process by high-resolution transmission electron microscopy and a time-resolved reflectance method. A single-pulse laser irradiation triggers melting of the silicon carbide surface, resulting in a phase separation into a disordered carbon layer with partially graphitic domains (∼2.5 nm) and polycrystalline silicon (∼5 nm). Additional pulse irradiations cause sublimation of only the separated silicon element and subsequent transformation of the disordered carbon layer into multilayer graphene. The results demonstrate viability of synthesizing ultra-thin nanomaterials by the decomposition of a binary system.

Role of lattice structure and low temperature resistivity in fast-electron-beam filamentation in carbon

The influence of low temperature (eV to tens-of-eV) electrical resistivity on the onset of the filamentation instability in fast-electron transport is investigated in targets comprising of layers of ordered (diamond) and disordered (vitreous) carbon. It is shown experimentally and numerically that the thickness of the disordered carbon layer influences the degree of filamentation of the fast-electron beam. Strong filamentation is produced if the thickness is of the order of 60 μm or greater, for an electron distribution driven by a sub-picosecond, mid-1020 Wcm−2 laser pulse. It is shown that the position of the vitreous carbon layer relative to the fast-electron source (where the beam current density and background temperature are highest) does not have a strong effect because the resistive filamentation growth rate is high in disordered carbon over a wide range of temperatures up to the Spitzer regime.

Interconnected Frameworks with a Sandwiched Porous Carbon Layer/Graphene Hybrids for Supercapacitors with High Gravimetric and Volumetric Performances

A facile approach to synthesize porous disordered carbon layers as energy storage units coating on graphene sheets to form interconnected frameworks by one‐step pyrolysis of the mixture of graphene oxide/polyaniline and KOH is presented. As effective energy storage units, these porous carbon layers play an important role in enhancing the electrochemical performances. The obtained porous carbon material exhibits a high specific surface area (2927 m2 g−1), hierarchical interconnected pores, moderate pore volume (1.78 cm3 g−1), short ion diffusion paths, and a high nitrogen level (6 at%). It displays both unparalleled gravimetric (481 F g−1) and outstanding volumetric capacitance (212 F cm−3) in an aqueous electrolyte. More importantly, the assembled symmetrical supercapacitor delivers not only high gravimetric (25.7 Wh kg−1 based on total mass of electroactive materials) but also high volumetric energy densities (11.3 Wh L−1) in an aqueous electrolyte. Furthermore, the assembled asymmetric supercapacitor yields a maximum energy density up to 88 Wh kg−1, which is, to the best of our knowledge, the highest value so far reported for carbon//MnO2 asymmetric supercapacitors in aqueous electrolytes. Therefore, this novel carbon material holds great promise for potential applications in energy‐related technological fields.

Fabrication of tin-filled carbon nanofibres by microwave plasma vapour deposition and their in situ heating observation by environmental transmission electron microscopy

Sn-filled carbon nanofibres (CNFs) are fabricated by microwave plasma chemical deposition. Scanning electron microscopy observations revealed the existence of a Sn island under the CNFs. The structure of the CNFs is investigated, and the behaviour of Sn in the internal space of CNFs is revealed by performing in situ heating observations by environmental transmission electron microscopy (ETEM). ETEM observations reveal that they have low-crystallized carbon wall and Sn occupies not only the CNF’s internal space but also its carbon wall. The Sn inside the CNF is completely covered by the carbon wall. Further, the in situ heating observations reveal that Sn within the internal space and the carbon wall of the CNFs diffused to the outside during heating. Moreover, it is found that higher membered carbon rings and defects in the graphite layer act as diffusion routes between disordered carbon layers.

High-Temperature Scanning Tunneling Microscopy Study of the Ordering Transition of an Amorphous Carbon Layer into Graphene on Ruthenium(0001)

The ordering transition of an amorphous carbon layer into graphene was investigated by high-temperature scanning tunneling microscopy. A disordered C layer was prepared on a Ru(0001) surface by chemical vapor deposition of ethylene molecules at ~660 K. The carbon layer grows in the form of dendritic islands that have almost the same density as graphene. Upon annealing of the fully covered surface, residual hydrogen desorbs and a coherent but still disordered carbon layer forms, with almost the same carbon coverage as in graphene. The ordering of this layer into graphene at 920 to 950 K was monitored as a function of time. A unique mechanism was observed that involves small topographic holes in the carbon layer. The holes are mobile, and on the trajectories of the holes the disordered carbon layer is transformed into graphene. The transport of C atoms across the holes or along the hole edges provides a low-energy pathway for the ordering transition. This mechanism is prohibited in a dense graphene layer, which offers an explanation for the difficulty of removing defects from graphene synthesized by chemical methods.

Catalytic oxidation of graphite by mass-selected ruthenium nanoparticles

The scanning tunneling microscopy and temperature programmed oxidation methods were used to study the catalytic oxidation of graphite by mass-selected Ru nanoparticles. Channeling by the nanoparticles was observed on the unsputtered HOPG basal surface at temperatures above 750 °C in 10 −6 mbar O 2 . Ar + ion bombardment was used to create layers of disordered carbon of various depths on the HOPG surface. The channel propagation rate in the disordered carbon layer was found to increase for larger nanoparticles. The depth of the interface between the disordered carbon layer and the graphite determined whether the nanoparticles etched paths parallel or perpendicular to the surface. The gasification onset temperature depended on the degree of graphitisation of the surface, with more heavily sputtered surfaces undergoing gasification at much lower temperatures than the unsputtered surface.

Novel electronic structure and transport properties of confined disordered carbon layers

AbstractWe propose a generalized spectral conductivity model for combined delocalized and localized π‐states of low‐dimensional carbon to explain their temperature dependent conductivity and its crossover. This model also interprets the origin of weakly localized coherent transport in carbon super‐structures such as nano‐crystalline diamond and 2D carbon films. From the enhanced phase coherence length the unique microstructure of these films is revealed. The corresponding electron's dephasing time also shows their potential for fast electronic device applications. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Photoluminescence and Raman spectroscopy of single diamond nanoparticle

The article reports techniques that we have devised for immobilizing and allocating a single nanodiamond on the electron beam (E-beam) lithography patterned semiconductor substrate. By combining the E-beam patterned smart substrate with the high throughput of a confocal microscope, we are able to overcome the limitation of the spatial resolution of optical techniques (~1 μm) to obtain the data on individual nano-object with a size range between 100 and 35 nm. We have observed a broad photoluminescence centered at about 700 nm from a single nanodiamond which is due to the defects, vacancies in the nanodiamonds, and the disordered carbon layer covered on the nanodiamond surface. We also observe red-shift in energy and broadening in linewidth of the sp3 bonding Raman peak when the size of the single nanodiamond is reduced due to the phonon-confinement effects.

Si–Cu/carbon composites with a core–shell structure for Li-ion secondary battery

Si–Cu/carbon composites with a carbon core and a Si–Cu composite shell have been synthesized by two-step mechanical fusion process. Large amount of pores around composite particles as well as the bridging disordered carbon layer between Si–Cu composite and carbon was the structural advantage of Si–Cu/carbon composite, which could prevent the electrochemical degradation induced by enormous volume changes during Li + insertion or extraction. With these structural characteristics, the cyclic property of Si–Cu/carbon composite was greatly improved compared to Si. A phase-controlled shell (Si–Cu composite) acted as another advantage for this Si–Cu/carbon composite, as it rendered not only good ductility for accommodating the volume expansion, but also enhanced kinetics.

Si–Ni–Carbon composite synthesized using high energy mechanical milling for use as an anode in lithium ion batteries

Si–Ni–Carbon composite was prepared by two-step high energy mechanical milling process. The microstructure was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometry (EDS). The electrochemical properties have been investigated until the 50th cycle. As a result, Carbon was coated on the surface of the Si–Ni composite, where Ni was distributed in Si matrix and the Si–Ni–Carbon composite demonstrated a large reversible capacity of ca. 960 with an excellent cycling stability. The reasons for good electrochemical characteristics were analyzed by high resolution transmission electron microscope (HR-TEM), powder resistance analysis and Barret–Joiner–Halendar (BJH) analysis. Uniformly dispersed Ni improved electronic conductivity and induced fast charge transport significantly in the Si–Ni–Carbon composite. In addition, pores and disordered Carbon layer played a role of media to accommodate a large volume change of Si during cycling. Our experiments suggest that the Si–Ni–Carbon composite should be a promising new anode material for lithium ion secondary batteries with a high capacity.