Artificial Graphite Research Articles

Ascorbic acid-assisted defect healing and stack ordering of graphene films towards high power thermal dispersion

The thermal dispersion power depends on thermal conductivity and thickness of the thermal dispersion material that is a critical component of modern electronic devices due to the demands of high operating power in a miniaturized space. Films made of assembled graphene flakes have been becoming an emerging thermal dispersion material owing to their high thermal conductivity and tunable thickness up to millimeters, which outperform that of artificial graphite films made from polyimide. But the thermal conductivity typically decreases with the increase of film thickness. In our work, by pre-reducing the graphene oxide with Vitamin C and sequentially annealing the stacking films at 2950 °C, a 80 μm-thick graphene film (GF) with an in-plane thermal conductivity of above 1600 W/(m·K) is achieved. Detailed characterizations indicate that, the addition of Vitamin C is beneficial to the assembly ordering of graphene oxide platelets and the defect healing during the thermal annealing, which both contribute to the excellent thermal conductivity of the films. Our work provides an industrially scalable strategy towards high performance heat dissipation films for future electronic devices.

Platinum Nanosheets Intercalated into Natural and Artificial Graphite Powders.

Insertion of sheet-type platinum particles (platinum nanosheets) between graphite layers was achieved by a thermal treatment of a mixture of platinum chloride (IV) and graphite powder (natural graphite or artificial graphite) under 0.3 MPa of chlorine at 723 K, followed by the treatment under 40 kPa of hydrogen pressure. Similar platinum nanosheets, which were 1-3 nm in thickness and 100-500 nm in width and had a number of hexagonal holes and edges with 120° angle, were formed between the layers of both natural graphite or artificial graphite; however, their location in the graphite layers depended on the type of graphite used. A number of platinum nanosheets were observed in the edge region of natural graphite particles which have flat surface. On the other hand, a number of platinum nanosheets were found inside and away from the edge of the artificial graphite particles especially in the vicinity of the cracks. Both the platinum nanosheet-containing artificial and natural graphite samples showed high selectivity to cinnamyl alcohol in cinnamaldehyde hydrogenation under supercritical carbon dioxide conditions, while spherical platinum particles, which were located on the surface of natural and artificial graphite, showed lower selectivity.

Real-time imaging of Na+ reversible intercalation in "Janus" graphene stacks for battery applications.

Sodium, in contrast to other metals, cannot intercalate in graphite, hindering the use of this cheap, abundant element in rechargeable batteries. Here, we report a nanometric graphite-like anode for Na+ storage, formed by stacked graphene sheets functionalized only on one side, termed Janus graphene. The asymmetric functionalization allows reversible intercalation of Na+, as monitored by operando Raman spectroelectrochemistry and visualized by imaging ellipsometry. Our Janus graphene has uniform pore size, controllable functionalization density, and few edges; it can store Na+ differently from graphite and stacked graphene. Density functional theory calculations demonstrate that Na+ preferably rests close to -NH2 group forming synergic ionic bonds to graphene, making the interaction process energetically favorable. The estimated sodium storage up to C6.9Na is comparable to graphite for standard lithium ion batteries. Given such encouraging Na+ reversible intercalation behavior, our approach provides a way to design carbon-based materials for sodium ion batteries.

ЭФФЕКТИВНЫЕ АКУСТИЧЕСКИЕ КОМПОЗИЦИОННЫЕ ПАНЕЛИ НА ОСНОВЕ ГРАФИТА

A set of experimental studies is carried out to determine the acoustic characteristics of three-dimensional panels of fixed thickness made of carbon-based composite material installed in the opening between the reverberation chambers. Sound insulation indices are determined when they are excited by a diffuse sound field in wide frequency ranges. The reverberation time in model chambers with different partition configurations is calculated. The optimal configuration of the partition with pyramidal cells to reduce the reverberation time in the rooms is determined. The use of graphite in the form of thin membrane applied to various surfaces can significantly reduce the sound pressure levels in the room and increase the sound insulation indices of air noise. In addition to thin membrane, graphite can be used as an additive in composite materials for sound insulation purposes. It is shown that the characteristics of such panels are quite universal. The measured acoustic characteristics of composite panels are compared with similar characteristics of traditional materials. It is determined that the composition belongs to the I group of fire-retardant efficiency and can be recommended for use as a fire-retardant material. The developed acoustic material is an effective absorbing agent that solves problems in architectural acoustics, echo cancellation in construction and architecture. Similar to metamaterials, natural and artificial graphites allow to solve these problems with small volumes and masses using simple and inexpensive technologies.

Achieving High-Performance Spherical Natural Graphite Anode through a Modified Carbon Coating for Lithium-Ion Batteries

The electrochemical performance of modified natural graphite (MNG) and artificial graphite (AG) was investigated as a function of electrode density ranging from 1.55 to 1.7 g∙cm−3. The best performance was obtained at 1.55 g∙cm−3 and 1.60 g∙cm−3 for the AG and MNG electrodes, respectively. Both AG, at a density of 1.55 g∙cm−3, and MNG, at a density of 1.60 g∙cm−3, showed quite similar performance with regard to cycling stability and coulombic efficiency during cycling at 30 and 45 °C, while the MNG electrodes at a density of 1.60 g∙cm−3 and 1.7 g∙cm−3 showed better rate performance than the AG electrodes at a density of 1.55 g∙cm−3. The superior rate capability of MNG electrodes can be explained by the following effects: first, their spherical morphology and higher electrode density led to enhanced electrical conductivity. Second, for the MNG sample, favorable electrode tortuosity was retained and thus Li+ transport in the electrode pore was not significantly affected, even at high electrode densities of 1.60 g∙cm−3 and 1.7 g∙cm−3. MNG electrodes also exhibited a similar electrochemical swelling behavior to the AG electrodes.

Nitrogen-doped porous graphitized carbon from antibiotic bacteria residues induced by sodium carbonate and application in Li-ion battery

Graphitic porous carbons with high electronic conductivity and abundant pores show great potential in many fields due to their unique physical and chemical properties. The traditional technique for the acquirement of artificial graphite is always conducted under high temperature above 2700 °C, leading to serious energy loss and high costs. In this study, antibiotic bacteria residues (ABRs), a kind of solid waste generated upon the production of antibiotics, are recycled into hollow-tunneled graphitic carbon derived from ABRs with N-doping (N-GC) using Na2CO3 as catalyst at 900 °C. Compared with graphitic carbon (G-AC) derived from ABRs at 2800 °C, the obtained N-GC shows a decent graphitization degree (69.8% vs. 57.0% of G-AC), high electronic conductivity (36.90 S cm−1 vs. 17.06 S cm−1 of G-AC at 20 MPa), well-developed porous structure as well as a high N containing amount (1.26% vs. 0.50% of G-AC). When used as anode material for Li-ion batteries (LIBs), the N-GC sample shows excellent electrochemical properties including good cyclability, long durability and good rate performance.

Morphological effect on high compaction density nickel-rich layered oxide cathodes during electrochemical lithiation and delithiation

The morphological effect of the blended single-crystalline Li[Ni0.8Co0.1Mn0.1]O2(NCM-C) and spherical secondary polycrystalline Li[Ni0.8Co0.1Mn0.1]O2(NCM-SP) cathodes (3:7 in weight) were systematically investigated. Calendering properties of the NCM-C, NCM-SP, and blended cathode were tested on a pilot-scale compactor. The values of maximal coating density and compaction resistance fitted by Heckel's equation indicate that the addition of moderate amounts of NCM-C into NCM-SP produced a significant improvement in the compaction degree and electrical conductivity of cathode laminate. The addition of NCM-C is also found to help reduce the generated electrode stress during electrochemical lithiation and delithiation which is confirmed by using the multi-beam optical sensor (MOS) technique. In the pouch-type full cell test utilizing artificial graphite as the negative electrode, the retained capacity is about 85.3% of its initial capacity by applying 1.0 C current at 25 °C after 700 cycles. The rate capability is also improved in the blended cathode even at a 2.0 C discharge rate, keeping 97.3% of its initial specific capacity (0.33C rate). It is suggested that the mixed electrode is considered to be a quite promising cathode electrode material to be applied for lithium-ion batteries.

Temperature dependence of the coefficient of thermal expansion of different artificial graphites and the dimensional change during heat treatment of carbonized specimens

Temperature dependence of the coefficient of thermal expansion of different artificial graphites and the dimensional change during heat treatment of carbonized specimens

Development of high temperature property measurements for artificial graphite materials and their analysis

Development of high temperature property measurements for artificial graphite materials and their analysis

Mechanical Properties of Bulk Graphite using Artificial Graphite Scrap as a Function of Particle Size

Mechanical Properties of Bulk Graphite using Artificial Graphite Scrap as a Function of Particle Size

Microstructure and thermal expansion behavior of natural microcrystalline graphite

Microcrystalline graphite (MG) is a major form of natural graphite and an important raw material with various applications in advanced technologies, such as lithium-ion battery anodes and isotropic graphite filler particles. MG is known to be an aggregate of graphite crystallites with a lateral dimension of less than 1 μm. However, the microstructure of MG remains unclear. In this study, we report the porous structure of a purified Chinese MG with an apparent density of 1.3–1.4 g/cm3. MG typically contains many microslits that are approximately 1–2 μm in length and up to 200 nm in width. The microslits provide MG with a stronger ability to accommodate c-axis thermal expansion than Mrozowski cracks, resulting in a low coefficient of thermal expansion (CTE) of approximately 2 × 10−6/K. This unique thermal expansion behavior makes MG a promising filler material for developing artificial graphite with a low CTE, and enables the modulation of the CTE of nuclear graphite.

Transformation of SnS Nanocompisites to Sn and S Nanoparticles during Lithiation

SnS nanomaterials have a high initial capacity of 1000 mAh g−1; however, this cannot be retained throughout electrochemical cycling. The present study provides insight into this capacity decay by examining the effect that Li intercalation has on SnS “nanoflowers” attached on carbon substrates’ such as artificial graphite. Scanning and transmission electron microscopy reveal that lithiation of such materials disrupts their initial morphology and produces free-standing Sn and SnS nanoparticles that dissolve in the electrolyte and disperse uniformly over the entire electrode surface. As a result, the SnS is rendered inactive after initial cycling and contributes to the formation of the solid electrolyte interface layer, resulting in continuous capacity decay during long term cycling. This is the first study that illustrates the morphological effects that the conversion mechanism has on SnS anodes. In order to fully utilize SnS materials, it is necessary to isolate them from the electrolyte by fully encapsulating them in a matrix.

Nanographenes from Distinct Carbon Sources

Abstract This article reports production protocols for nanographenes and the effect of the reaction conditions on their structures and optical properties. These fundamental studies are of value for exploring suitable reaction conditions for the production of nanographenes with desirable properties. Graphite, finely crushed graphite powders, and artificial graphite, all of which are commercially available, are employed. Nanographenes are produced by the acid-assisted oxidative cleavage of the parent carbons followed by neutralization and deionization. The use of dialysis membranes for the size separation of nanographenes offers nanographenes with a specific size distribution, thereby allowing their structures and optical properties to be compared. Experiments demonstrate that small amounts of acids (60 ml of conc. H2SO4 and 20 mL of 60% HNO3) and oxidation for 12 h promotes a more efficient and cost-effective production of nanographenes from 2 g of a carbon source. The functionalization of the nanographene edges with p-propargyloxybenzyl amine confirms that the armchair edge with two carboxy groups is the dominant edge structure, irrespective of the carbon source.

Определение эффективной температуры обработки углеродных материалов в высокотемпературных печах по параметрам спектроскопии комбинационного рассеяния образцов-свидетелей

The aim of this work is to evaluate the use of Raman spectroscopy of carbon fibre-based (CF) reference samples for establishing the heat treatment temperature (HTT) in high-temperature (1000 – 3000 °C) furnaces used in production of a series of carbon materials. Based on obtained correlational relationships between Raman spectroscopy parameters and HTT, the use of the ID/IG parameter is suggested for obtaining the most exact and reproducible results. An experimental basis for the use of polyacrylonitrile-based (PAN) CF as reference specimens is provided. It is shown that for PAN-based CF samples treated in the high temperature interval (1000 – 3000 °С) the ID/IG parameter correlates well with X-Ray diffraction analysis parameters. A series of Raman spectroscopy of reference specimens potential uses the in determination of effective HTT of carbon materials in technological processes of production of carbon-carbon based composite materials, artificial graphites and PAN-based CF’s and in the determination of temperature fields of laboratory and industrial equipment for high-temperature treatment of carbon materials in the temperature interval 1000 – 3000 °C, specifically Tamman, vacuum electric resistance and Acheson furnaces, are examined.

电沉积还原氧化石墨烯对人造石墨锂离子电池负极材料电化学性能的影响

电沉积还原氧化石墨烯对人造石墨锂离子电池负极材料电化学性能的影响

Na0.76V6O15/Activated Carbon Hybrid Cathode for High-Performance Lithium-Ion Capacitors

Lithium-ion hybrid capacitors (LICs) are regarded as one of the most promising next generation energy storage devices. Commercial activated carbon materials with low cost and excellent cycling stability are widely used as cathode materials for LICs, however, their low energy density remains a significant challenge for the practical applications of LICs. Herein, Na0.76V6O15 nanobelts (NaVO) were prepared and combined with commercial activated carbon YP50D to form hybrid cathode materials. Credit to the synergism of its capacitive effect and diffusion-controlled faradaic effect, NaVO/C hybrid cathode displays both superior cyclability and enhanced capacity. LICs were assembled with the as-prepared NaVO/C hybrid cathode and artificial graphite anode which was pre-lithiated. Furthermore, 10-NaVO/C//AG LIC delivers a high energy density of 118.9 Wh kg−1 at a power density of 220.6 W kg−1 and retains 43.7 Wh kg−1 even at a high power density of 21,793.0 W kg−1. The LIC can also maintain long-term cycling stability with capacitance retention of approximately 70% after 5000 cycles at 1 A g−1. Accordingly, hybrid cathodes composed of commercial activated carbon and a small amount of high energy battery-type materials are expected to be a candidate for low-cost advanced LICs with both high energy density and power density.

Eco-conversion of coal into a nonporous graphite for high-performance anodes of lithium-ion batteries

Porous carbons are always proposed as electrode materials of lithium-ion batteries (LIBs); however, their high porosity and large surface areas lead to severe side reactions with electrolytes. Here, a new kind of non-nanopore carbon was designed for the anode material of LIBs. It was prepared from catalytic synthesis of a porous carbon from coal followed with graphitization. The graphitization removes the micro/mesopores of the porous carbon, and creates a new kind of carbon with very limited porosity and defects, which can evade side reactions with electrolytes. The resultant structure of the material can facilitate ion transport, provide a good conductivity, and alleviate the stresses experienced in repeated charge/discharge. The material exhibits excellent lithium-storage properties, including a high reversible capacity of 347 mAh g−1 and high cycling stability (no capacity fading during 1000 cycles). The material might be an alternative to artificial graphite considering its facile preparation and excellent performance.

Nano-Si/C Composite Via Carbothermal Shock for Lithium Ion Battery Anode

Nowadays, Li-ion batteries are ubiquitous and dominate the portable storage market. However, their utilizations for high-energy applications are limited and they present huge social challenges for the future, especially for the applications to electric and hybrid electric vehicles (EVs and HEVs respectively). One strategy, praised by both academics and industry, the high capacity electrode materials, notably silicon, as it is considered an attractive graphite substitute in Li-ion battery anode. Silicon (Si) is recognized as a representative anode material for next-generation lithium-ion batteries due to properties, such as a high theoretical capacity, suitable working voltage, and high natural abundance. However, inherently, a large volume expansion (~ 400%) during lithiation/delithiation introduces poor electrical conductivity and unstable solid electrolyte interfaces (SEI) films, the Si-based anodes possess serious stability problems hindering practical applications. To overcome the issue, Si-nanoparticles(Si-NPs) has been proposed as a promising solution to overcome the volume expansion and the flowing fracturing problems of the micron-size particles. Thus, various nanoparticles and nano-objects (0D, 1D, 2D and 3D) have been tried for the Li battery anode in the last decade.1, 2 It has been demonstrated that Si-NPs smaller than 150 nm can be avoided the further fracturing upon the repeating lithiation.We propose a technology for preparations of novel Si-NPs/carbon(Si/C) composites on the basis of thermal shock of the carbon materials such as natural and artificial graphites. We developed a facile, one-step carbothermal shock method for transformations from micro-Si to Si-NPs less than 150 nm size and well dispersed on carbon matrix (Figure 1.). The particle size distribution of the Si-NPs was narrow and the dispersion was uniform. The Si/C composite anode exhibited a high specific capacity (>1,000 mAh/g) and predominant fast charging behavior. Reference [1] R. Chen, T. Zhao, X. Zhang, L. Li and F. Wu, Advanced cathode materials for lithium-ion batteries using nanoarchitectonics, Nanoscale Horiz., 2016, 1, 423-444[2] D. Ma, Z. Cao and A. Hu, Si-Based Anode Materials for Li-Ion Batteries: A Mini Review, Nanomicro Lett., 2014, 6(4), 347-358Figure 1. SEM images of Si-NPs/carbon (Si/C) composites Figure 1

Effect of Petroleum Pitch-Coating on the Electrochemical Performance of Graphite As Anode Materials

Lithium ions batteries (LIBs) have become the most promising energy storage device in new energy field due to their potential utility as high-energy-density batteries for electric vehicles and hybrid electric vehicles. Graphite, which is the most widely commercialized anode material of LIBs, exhibits structural stability and excellent cycle characteristics. However, graphite has some problems to overcome. Due to the uneven SEI (Solid Electrolyte Interface) layer generated after the initial cycle, considerable irreversible capacity loss occurs. This results in electrode collapse and cycle instability especially in high-rate charging. Therefore, many researchers have been reported to improve the stability of graphite with carbon coating.In this study, electrochemical characteristics of artificial graphite coated with petroleum pitch were investigated as anode materials of lithium ion batteries. To improve the capacity and stability of graphite, it was coated with petroleum pitch(SP, 150, 200 and 250 ℃). The physical properties of prepared samples were analyzed by MALDI-TOF, TGA, XRD, SEM and TEM. The electrochemical performances of graphite composites as an anode were evaluated by initial charge/discharge, cycle, rate performance, cyclic voltammetry and electrochemical impedance spectroscopy (EIS) tests. The electrolyte used in the half cell was 1.0 M LiPF6 dissolved in organic solvents (EC:DEC=1:1 vol%).It was found that the pitch(SP 250 ℃) anode materials had excellent electrochemical characteristics: good initial efficiency (92.9%), discharge capacity (343 mAh/g), cycle stability (97%), and rate performance (84.1% in 10 C/0.1 C) than that of pristine graphite.

A novel scalable synthesis of high-rate performance silicon anode materials by liquid-phase coating doping method

Recycled solar grade p-type silicon (Si) broken wafers (1–10 Ω·cm) were milled to Si powders, and then doped with phosphoric acid to make n-type Si powders with extremely high conductivity for being used as anode materials for lithium ion batteries. The electrical conductivity of as-obtained phosphorus-doped (P-doped) Si powders is as high as 5263.18 μs/cm, which is nearly 5 × 103 times higher than undoped Si (1.04 μs/cm). The charge specific capacity of P-doped Si holds 1920.3 mAhg−1 after 50 cycles at 0.84 A g−1, when the charge current density increased to 21 A g−1 (only take 12 min for charging), it still maintains at 1758.5 mAhg−1 after 50 cycles. This proves the outstanding cycle stability of P-doped Si at high rate, which can be attributed to the improved conductivity and lithium ion diffusion coefficient. For practical application in full cells, P-doped Si was composited with artificial graphite to be used as the anode, and the cathode adopted was commercial LiNi0.5Co0.2Mn0.3O2, which also discloses excellent long cycle stability with a high capacity retention of 80.7% even after 700 cycles at 0.5C (1C = 420 mA g−1).