Artificial Graphite Research Articles

Preparation and properties of ceramic-based conductive coatings

Ceramic-based conductive coatings were prepared by sol–gel method with artificial graphite (CGM) as conductive fillers and methyltrimethoxysilane (MTMS) and silica sol as dispersion medias. The graphene (Gr) and carbon black (CB) were added to improve the properties of the resultant coatings. The results showed that the electrical conductivity and thermal stability of coatings were improved by the addition of Gr and the electrical conductivity of coatings was further improved by the addition of CB for decreasing the pores of coatings. When the amount of CGM was 15.0 wt% with adding 1.0 wt% Gr and 0.5 wt% CB in the coating, the resistivity of obtained coating reduced to 1.46 Ω·cm and its adhesion increased to 3911.62 mN. The prepared coating presented excellent electrical conductivity and adhesion properties, which was much better than the coating prepared without adding Gr and CB.

Simultaneous Interphase Optimizations on the Large-Area Anode and Cathode of High-Energy-Density Lithium-Ion Pouch Cells by a Multiple Additives Strategy.

Prior to the maturation of next-generation energy storage devices, the actual lithium-ion batteries for commercial purposes are still expected to fulfill some critical requirements, among which the high energy density, wide operating temperature range, and related long-term cycling stability are the most challenging issues. Herein a multiple additives strategy is employed to simultaneously optimize the solid electrolyte interphase on the large-area anode and cathode in a 2 Ah artificial graphite (AGr)/LiNi0.5Co0.2Mn0.3O2 (NCM523) pouch cell with high gravimetric (>260 Wh kg-1) and volumetric (>630 Wh L-1) energy density. By introducing a rational mixture of electrolyte additives, a highly sulfurized surface layer and a uniform and thin passivation layer are separately formed on the anode and cathode of the AGr/NCM523 pouch cell, exhibiting high storage stability at 60 °C, much improved discharge capacity at -10 and -20 °C, high anodic stability at high voltage of 4.4 V, and stable cyclic performance with a capacity retention of 85.5% after 500 cycles, significantly outperforming the value of 75.7% after only 200 cycles of the cell without additional additives. These results demonstrate the critical effect of simultaneous optimizations of anode and cathode interphase layers to construct stable high-energy-density lithium-ion pouch cells.

Expansion / shrinkage of bottom masses hearth during firing

The actualization of the problem of shrinkage phenomena in the process of firing the bottom, contributing to the opening of joints and the formation of cracks, is shown. The modern methods and means of studying expansion / shrinkage of the bottom masses during firing are analyzed. The expansion / shrinkage of bottom masses, differing in the ratio of the carbon component (anthracite) and artificial graphite in their composition, was investigated. It has been established that shrinkage phenomena decrease in a row from anthracite mass to graphitoanthracite. Studies have shown that the difference in the scale of linear changes during structural shrinkage is quite significant ― about 20 %. It was noted that the minimization of shrinkage phenomena contributing to the opening of joints and the formation of cracks is one of the factors to reduce the risk of leakage of the bottom of the cell. In this regard, it is advisable to optimize the rate of shrinkage of the bottom masses during the firing process at the stage of its structural adjustment, taking into account the conditions of their operation

The Control of Volume Expansion and Porosity in Carbon Block by Carbon Black (CB) Addition for Increasing Thermal Conductivity

The graphite block as a phase change materials (PCMs) was manufactured by graphitization of a carbon block. Carbon blocks were prepared by filler (cokes or graphite) and binder (pitch). The binder-coated filler was thermally treated for carbonization. The gases generated from the evaporation of low molecular weight components in the binder pitch during the carbonization process were not released to the outside. Consequently, porosity and volume expansion were increased in artificial graphite, and thereby the thermal conductivity decreased. In this study, to prevent the decrease of thermal conductivity in the artificial graphite due to the disadvantages of binder pitch, the carbon block was prepared by the addition of carbon black, which can absorb low molecular weight compounds and release the generated gas. The properties of the prepared carbon blocks were analyzed by SEM, TGA, and thermal conductivity. The addition of carbon black (CB) decreased the porosity and volume expansion of the carbon blocks by 38.3% and 65.9%, respectively, and increased the thermal conductivity by 57.1%. The CB absorbed the low molecular weight compounds of binder pitch and induced the release of generated gases during the carbonization process to decrease porosity, and the thermal conductivity of the carbon block increased.

Determining the Size of Mosaic Blocks and Anisometry of the Flakes of Artificial Graphite by Magnetoresistance

The article presents the results of the mathematical modeling of the flow of the electric current in a lamellar graphite polycrystal in a magnetic field. In contrast to the simple model, which takes into account only the contact resistance between the flakes, this model also takes into account the ohmic resistance along and across the layers of graphite based on the chain model of the flow of the electric current in a graphite polycrystal. As a result, a formula with refined correction coefficients is obtained, which allows us to choose polycrystal parameters for calculating the temperature dependence of resistivity and magnetoresistance. A comparison is made with a simple model that takes into account only contact resistance, the difference is up to 50% from the previous estimate. The difference is explained by the peculiarities of the connection of crystallites in a polycrystal. This allows analyzing the size of the crystallites and their connections in artificial graphite based on its electrophysical properties.

Study Performance of LiFePO4/Graphite Cylindrical Pouch Cell

Cylindrical cell Lithium ion battery with a pouch casing has been made at the Integrated Battery Laboratory, BATAN. LiFePO4 double sided coated aluminum foil with a thickness of 180 μm is used as a cathode sheet. The anode sheet is made from two-sided artificial graphite coated on copper foil with a thickness of 197 μm. The composition, crystal structure, of the coated LiFePO4 was measured by XRD. Battery cells are built by rolling thin layers of cathode, separator, and anode material into cylindrical shape using a rolling machine. The cylindrical cell is inserted into an aluminum bag and then sealed at 175°C. Cylindrical cell-bag inserted into the Glove Box then filled with ∼ 2.5 ml of LiPF6 electrolyte liquid. A vacuum sealing machine is used to seal the remainder of the bag set at 175 oC. The performance of lithium ion batteries is characterized by using a battery analyzer. LiFePO4 shows a release capacity of 250.00 mAh, with a specific capacity of 124.10 mAh/g in the 1st cycle and 100.20 mAh/g after 100th cycle, at a rate of 0.3C. The cell shows good performance after 100 cycles with 80.74% retention.

Expansion/Shrinkage of Hearth Mixes During Firing

The urgency of the problem of shrinkage phenomena during hearth firing, contributing to joint opening and crack formation, is demonstrated. Contemporary methods and means of studying expansion/shrinkage of hearth mixes during firing are analyzed. Expansion/shrinkage of hearth mixes, differing in the ratio of the carbon component (anthracite) and artificial graphite within their composition, is investigated. It is established that shrinkage phenomena decrease in a series from anthracite to graphite-anthracite. Studies show that the difference in the scale of linear changes during structural shrinkage is quite significant, i.e., about 20%. It is noted that minimization of shrinkage phenomena contributing to opening of joints and crack formation is one of the factors for reducing the risk of leakage at the bottom of a cell. In this connection it is advisable to optimize the shrinkage rate of hearth mixes during firing in the stage of structural adjustment taking account of operating conditions.

Fast Production of High Performance LiNi0.815Co0.15Al0.035O2 Cathode Material via Urea-Assisted Flame Spray Pyrolysis

The high throughput and rapid flame-assisted spray pyrolysis method has been adapted to synthesize cathode materials LiNi0.apCo0.15Al0.035O2 (NCA). This method is considered low cost and simple. By varying the precursor solution concentration and sintering temperature, the optimal condition was established at temperature sintering of 800 °C and precursor solution concentration of 1 M. X-ray diffraction patterns showed the as-prepared NCA particles exhibit a pure well-ordered hexagonal layer structure with high crystallinity. Polyhedral shaped micro-sized particles are confirmed by SEM images. Galvanostic charge–discharge tests were conducted using cylindrical full-cell utilizing artificial graphite as the anode. The highest specific initial discharge capacity measured between 2.7 and 4.3 V is 155 mAh g−1 with capacity retention of 92% after cycled at 0.2 C for 50 cycles. Thus, this method is considered as a satisfying approach for NCA mass production.

Facile synthesis of FeVO@C materials as high-performance composite cathode for lithium-ion hybrid capacitor

Abstract Due to its excellent power performance and high cycling stability, activated carbon is widely used as the cathode in Li-ion hybrid capacitors. However, it remains challenging to improve its energy density. In this article, we report a composite cathode material composed of iron vanadate (Fe5V15O39(OH)9·9H2O) (FeVO) particles and commercial activated carbon (YP50D), synthesized by a facile wet-chemical approach. The successful combination of the two materials results in the simultaneous action of electric-double-layer capacitive effects and a diffusion-controlled faradaic process during the charging-discharging cycles, enabling improved energy. LIC devices are fabricated using 10-FeVO@C as the cathode and pre-lithiated artificial graphite as the anode. Compared to pure YP50D, the 10-FeVO@C//AG LIC device delivers a much higher energy density of 117.9 W h kg−1 at a power density of 237.6 W kg−1 and retains 27.3 W h kg−1 at 20008.7 W kg−1. A reasonable cycling stability is achieved as well, with a capacitance retention of 70.7% after 1000 cycles. This work proves the great potential of composite cathodes, with the combination of a battery material and activated carbon, for high-performance lithium-ion hybrid capacitors.

Physical vapor deposition of TiO2 nanoparticles on artificial graphite: an excellent anode for high rate and long cycle life lithium-ion batteries

Artificial graphite powder (AGP) is one of the utmost common anode materials for lithium-ion batteries (LIB). Nevertheless, the dissolution of the anode material into the electrolyte is one of the main challenges that causes the vanishing capacity and poor cyclability. In this study, a nanoscale TiO2 film is uniformly sputtered on the surface of bare artificial graphite (BAG) electrode through the physical vapor deposition (PVD). The results obviously prove that TiO2 film is completely and homogeneously covered on the BAG electrodes. BAG and AG/TiO2 electrodes represent discharge capacities of 339.3 and 369 mAh g−1 at first cycle, respectively. Therefore, the nano-layer coating of TiO2 increases the initial discharge capacity of artificial graphite around 9%. After 100 cycles, the values of capacity retention at a current density of 0.5 C are 88.7 and 94.2% for BAG and AG/TiO2, respectively. The discharge specific capacity of pouch full cells using BAG and AG/TiO2 anodes versus NCA cathode reveals that AG/TiO2 anodes could still provide a high reversible capacity of around 123.05 mAh g−1 after 10 cycles at a high current density of 4 C. This corresponds to 346.5% improvement compared with BAG anodes versus NCA cathode at 4 C.

Effect of Pitch-Coating on the Electrochemical Chracteristics of Graphite As Anode Materials for Lithium Ion Battery

Lithium ions batteries (LIBs) have become the most promising energy storage device in 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 ℃) coated graphite as anode materials had excellent electrochemical characteristics: initial efficiency (92.9%), discharge capacity (343 mAh/g), cycle stability (97%), and rate performance (84.1% in 10 C/0.1 C) than those of pristine graphite.

Fluorine-doped SnO2/reduced graphene oxide-artificial graphite hybrids as lithium-ion battery anodes with stable capacity

A series of hybrid anode materials for Li-ion battery were successfully prepared by mechanically mixing artificial graphite (AG) with fluorine-doped tin oxide/reduced graphene oxide (F-SnO2/rGO) obtained via hydrothermal treatment in a mass ratio of 1:3, 1:4, and 1:6 respectively (denoted as F-SnO2/rGO-xAG, x = 3, 4, 6). Compared with the widely used artificial graphite, all the F-SnO2/rGO-xAG hybrids delivered higher reversible capacity and exhibited superior electrochemical stability upon cycling. In the case of these hybrid materials, the F-SnO2/rGO-4AG hybrid maintained stable reversible specific capacities of 440 mAh g−1 at 500 mA g−1 with a high capacity retention of 96.28% after 500 cycles. Therefore, the outstanding electrochemical performance reveals that the hybrid materials possess great potential as anodes for high-performance Li-ion batteries.

Определение адсорбционной активности удельной поверхности искусственного графита по индикатору метиленовому голубому

This article investigated and determined the specific surface area of artificial graphite for adsorption through a methylene blue solution. The study showed that the specific surface area of graphite adsorption obtained from coal from the Uzgen deposit in Kyrgyzstan for methylene blue is 599.4 m2/g and this is very close to the performance of activated carbons. The specific surface area of artificial graphite obtained from coal from the Uzgen deposit for adsorption activity was determined by titration of a suspension with a methylene blue indicator solution.

Effect of Carbonaceous Components on Tribological Properties of Copper-Free NAO Friction Material.

Copper helps to accelerate heat transfer during the braking process, allowing the brake materials to produce a stable coefficient of friction (COF), which in turn reduces wear loss and braking noise. However, its properties are also quite harmful to aquatic organisms. Finding a suitable replacement that fits all functions of copper for brake materials is not an easy feat. In this paper, six different carbonaceous components (coke, carbon black, carbon fiber, artificial graphite, natural graphite and expanded graphite) were substituted for copper in non-asbestos organic (NAO) friction materials. The hardness, thermal conductivity and tribological behaviors of these copper-free NAO friction materials were examined. Experimental results indicate that carbonaceous components improve lubrication and assist the friction composites with generating friction layers on the worn surface. Specimens containing coke, carbon black or carbon fiber exhibit broken friction layers, whereas specimens containing artificial graphite, natural graphite or expanded graphite exhibit quite adherent and smooth friction layers. Among all the copper-free carbon containing specimens, the specimen containing expanded graphite appears to be the best choice. It has the highest thermal conductivity, a relatively low wear loss and a relatively high and stable COF.

Preparation of petaloid graphite nanoflakes in molten salt for high-performance lithium-ion batteries

The high value-added utilization of inferior resources has grown up an urgent need. Artificial graphite with petaloid nanoflakes was prepared from inferior coal by molten salt electrolysis method. The as-prepared graphite was used in lithium-ion batteries, which exhibited a high reversible specific capacity of 848.26 mA h g−1 after 120 cycles with a current density of 1 A g−1. Even at an ultra-high current density of 10 A g−1, it still delivered a high specific capacity of 277.2 mA h g−1 as well as an excellent rate performance. These superiorities make synthetic graphite based on inferior coal a very promising anode materials for high-performance lithium-ion batteries.

Effects of purification on the properties and microstructures of natural flake and artificial graphite powders

As the main components of the matrix graphite of pebble fuel elements for HTR-PM, the natural flake graphite powder (NFGP) and artificial graphite powder (AGP) must present suitable microstructural features such as specific surface area (SSA), particle size distribution (PSD), and ash contents. As a regular method, the graphite powders are purified at high temperature of ~2500 °C with the purge of halogens to obtain their high purity prior to the powder treatments such as pulverizing, shaping, and particle classification, which may introduce impurities into the graphite powders during the powder treatment process. Therefore, the purification of NFGP and AGP should be carried out after the powder treatment to prevent the graphite powders from being contaminated and reduce the cost. In this manuscript, the microstructural features of NFGP and AGP before and after purification were comparatively analyzed to figure out the effects of purification process on the microstructures of NFGP and AGP. Results showed that purification had great influences on the ash contents and the contents of impurity elements, SSA, and degree of graphitization of graphite powders. However, the purification had little influence on the PSD of graphite powders. The significant decrease of SSA of graphite powders through the purification was due to the reduction of BJH adsorption cumulative volume and porosity. Comparing with those of the NFGP, the properties and microstructure of the AGP changed more through the purification process, which was probably due to the original un-graphitized coke of AGP before purification.

Electrochemical performance enhancement of porous Si lithium-ion battery anode by integrating with optimized carbonaceous materials

Silicon (Si) is regarded as a promising negative material for Li-ion batteries (LIBs), but the poor cyclic performance limits its practical applications. Herein, we used several different carbonaceous materials as carbon sources to form Si/C composites, which was formed by etched Fe–Si alloys followed by mechanical ball mill mixing with carbon. It is found that the artificial graphite as the carbonaceous material can form a well-distributed mixture during the ball milling, and then uniformly coated with amorphous carbon pyrolyzed by the phenolic resin. The pore structure of Si particles can provide rapid diffusion for lithium ions, resulting in improving the electrochemical properties. The well-coated carbon layer promotes the formation of stable SEI layer on the composites surface, which is advantageous for the long cycle performance. The carbonaceous materials (artificial graphite, flake graphite and soft carbon) have remarkable influence on the electrochemical performance of Si/C composites. The silicon/graphite-artificial graphite (Si/C-AG) exhibits the best performance among these three Si/C composites. It delivers a specific capacity of 445 mAh g-1 at 0.5 A g−1 with a retention of 94% after 200 cycles. This work would be helpful with choosing suitable carbonaceous materials for the Si/C composites.

Effects of Graphite Heat-Treatment Temperature on Single-Crystal Li[Ni5Mn3Co2]O2/Graphite Pouch Cells

In this work, the effect of the heat-treatment temperature of synthetic (artificial) graphite on the electrochemical performance of LiNi0.5Mn0.3Co0.2O2/graphite pouch cells was explored and compared with cells utilizing commercial-grade artificial and natural graphite materials. Two optimized electrolyte additive blends, 2% VC + 1% DTD and 1% LiPO2F2, were used in the cells tested. Physical properties of the different graphite electrodes, such as morphology, pore-size, crystallinity and thermal stability were investigated. Then, cells with each graphite material were tested with a variety of electrochemical techniques: ultra-high precision coulometry, long-term cycling, high-rate cycling, isothermal microcalorimetry, operando pressure tests and open circuit storage tests. Marginal benefits were found in electrochemical tests for cells with graphite materials that had been heat-treated to lower temperatures. However, in all tests, cells with synthetic graphite had superior performance compared to natural graphite.

Quinone‐Based Redox Supercapacitor Using Highly Conductive Hard Carbon Derived from Oak Wood

AbstractIn this study, the use of biorefined wood materials in the fabrication of organic redox supercapacitors is proposed. Oak‐derived hard carbon (HC) is revealed to have a nanographite domain structure, showing conductivity as high as that of artificial graphite. The CO2‐activated hard carbon (A–HC) has a conductivity one order higher than that of commercial activated carbon, with a surface area of 1126 m2 g−1. The energy densities of supercapacitors composed of a tetrachlorohydroquinone cathode and anthraquinone (AQ) or 1,5‐dichloroanthraquinone (DCAQ) anode are 19.0 and 13.8 Wh kg−1, respectively. The utilization rate of AQ with A–HC is 97.6% (250.9 mAh g−1), which is much higher than those in previous reports (≈80%). After 1000 cycles, 91.0% of the discharge capacity is retained when the DCAQ anode is used. Biorefined wood materials lead to a remarkable improvement in the operation of organic supercapacitors. This is intriguing, because the functional carbon material herein is easily prepared from a natural resource, wood, whereas numerous studies have prepared such materials from artificial chemical sources. Therefore, the use of oak‐derived HC enhances the usability of organic active materials for energy storage devices and potentially has a far‐reaching impact on the environment.

Selective removal of nanopores by triphenylphosphine treatment on the natural graphite anode

Artificial graphite (AG) and natural graphite (NG) have different physical properties, which should have significant effects on their unique electrochemical characteristics: NG is known to have superior specific capacity and low cost, whereas AG shows superior cyclability and low-swelling characteristics. Herein, we present a straightforward strategy using triphenylphosphine to improve NG, enabling its physical properties to resemble those of AG and thereby improving its cyclability and swelling characteristics. The volume of a-few-nanometer-sized pores of NG is significantly reduced by triphenylphosphine treatment, which is similar to that of the AG. As a result, triphenylphosphine-treated NG (TPP) anode shows improved cyclability (83.6% after 300 cycles) compared to that of NG, confirming the correlation between nanopore volume and cyclability. Furthermore, the expansion of single-layer pouch cell prepared with TPP, as monitored by in situ thickness measurement, is suppressed to 9% after 55 cycles, which is superior to the pristine NG showing 14% expansion after the same number of cycles. Electrochemical impedance analyses of symmetric cells reveal that the changes of ionic and solid-electrolyte interface (SEI) resistance are accompanied by the reduction of nanopores, confirming that the formation of decreased SEI layer is a crucial factor for realizing less-swelling and highly durable anodes based on the cost-effective NG materials.