Surface Modification Of Graphite Research Articles

A review on graphite surface modification methods towards low carbon-containing refractories

A review on graphite surface modification methods towards low carbon-containing refractories

Graphite surface modification by quasi-periodically structured diazonium monolayer

In this study, a novel functionalization protocol of highly oriented pyrolytic graphite (HOPG) was proposed, in which a two dimensional (2D) porous network formed by alkoxy-substituted dehydrobenzo[12]annulene (DBA-OC12) was served as a sacrificial template for electrografting of 3,5-terbutyl diazonium (3,5-TBD). The 2D DBA-OC12 porous network was synthesized by drop-casting of the corresponding precursor followed by a drying process. The structural and electrochemical properties of pristine as well as functionalized HOPG surfaces were investigated by means of cyclic voltammetry (CV) and scanning tunneling microscopy (STM).

Surface Decoration of TiC Nanocrystals onto the Graphite Anode Enables Fast-Charging Lithium-Ion Batteries.

To significantly reduce the charging time of commercial lithium-ion batteries (LIBs), it is essential to control the surface properties of graphite anodes because the charging process involves sluggish interfacial kinetics between graphite and the electrolyte. For the effective surface modification of graphite, herein we demonstrate the surface decoration with titanium carbide (TiC) nanocrystals onto graphite particles via a simple wet-coating process. The high electrical conductivity, low Li+ adsorption energy, and small surface diffusion barrier of the TiC nanocrystals facilitate fast Li+ adsorption and migration in the graphite surface by reducing the overpotential upon the charging process. The feasibility of the TiC nanocrystal-decorated graphite (TiC@AG) anode is thoroughly examined with an in-depth understanding of the interfacial reaction mechanism. Furthermore, the full-cell with a commercial cathode (LiNi0.8Co0.1Mn0.1O2) and TiC@AG anode demonstrates an impressive capacity retention (94.5%) after 300 cycles under fast-charging condition (3 C-charging and 1 C-discharging) without any sign of Li plating. The charging time of the TiC@AG full-cell was estimated at 16.2 min (80% of state of charge), which is substantially shorter than that of the artificial graphite full-cell. Our findings offer practical insights into the design principles of advanced graphite anodes, contributing to the realization of fast-charging LIBs.

Electrochemical grafting assisted modification of graphite surface by 3,4,5-trimethoxybenzenediazonium based monolayer

A conventional route to create such nanoscale electronic devices using the autonomous ordering and assembly of organic molecules on atomically well-defined surfaces has been proposed. However, these thin films are unstable in realistic environments due to weak interaction between the organic molecules and crystal surfaces. Therefore, enhancing the interfacial interaction between them is assigned as the key approach to extend the scope of application of these promising monolayer thin films. In this work, we demonstrate the formation of an organic monolayer, namely 3,4,5-trimethoxy diazonium (3,4,5-TMD), on a Highly Ordered Pyrolytic Graphite (HOPG) electrode by using the power of electrochemical method. The structural properties at the nano scale as well as the bonding nature between 3,4,5-TMD adlayer and HOPG electrode at the interface were investigated by a combination of cyclic voltammetry (CV), atomic force spectroscopy (AFM) and Raman spectroscopy. As a result, the 3,4,5-TMD molecules covalently bond to carbon atoms located at the HOPG interface for forming a monolayer with its thickness of 0.92 ± 0.02 nm. This finding opens a partway to apply the electrochemical grafting for covalent functionalization of 2D materials on HOPG and other metallic surfaces.

Electric discharge coating on graphite using W–Cu sintered tool

ABSTRACT This article describes about the modification of graphite surface by depositing a hard layer of tungsten (W) and copper (Cu) material using electrical discharge machining (EDM) setup in reverse polarity. The sintered tool is prepared by heating a Powder Metallurgical (P/M) green compact of 75%W-25%Cu at 900 0C in an argon atmosphere. The deposited layer is studied by evaluating the Tool Wear Rate (TWR), Material Deposition Rate (MDR), and Surface Roughness (Ra). The coating is characterized by FESEM, EDS, and XRD analyses. The existence of tool particles (W and Cu) and carbides of tungsten (WC and W2C) are witnessed on the graphite surface. The tool materials are impinged up to 19.93 µm of depth from the surface level. The experimental results show an increase in thickness of the coating with increased peak current settings. Minimum thickness of 15.46 µm and maximum thickness of 33.93 µm are found in the experimentation.

Surface modification of graphite by low‐temperature oxygen plasma and SnO2FeO(OH) coatings for lithium storage

AbstractGraphite powders are exfoliated by Li+/Na+ co‐intercalation to obtain exfoliated graphite, and then the surfaces are modified with oxygen‐containing functional groups by oxygen plasma etching to alter the chemical properties of surface. For advanced graphite anodes of lithium ions batteries, here fine‐structured SnO2FeO(OH) coatings are constructed on the oxidated surfaces of graphite by an electrostatic adsorption method. Electrochemical tests show that surface modified graphite has higher capacity and better rate performance than pristine graphite, and the specific discharge capacity is reached to 400 mAh g−1 at a current of 37.2 mA g−1 (0.1C), which is increased by 27.8% compared with the pristine graphite anode.

Succinimide-modified graphite as anode materials for lithium-ion batteries

Surface modification of graphite and the use of electrolyte additives are two effective ways to stabilize the performance of graphite anodes and to extend the life of lithium-ion batteries (LIBs). In this study, these two methods are combined by chemically bonding succinimide and N-phenylsuccinimide fragments (-SI and -PSI) to the graphite (G) surfaces, respectively, via the Diels-Alder (D-A) reactions. Two modified graphite materials (G-SI and G-PSI) are prepared and their electrochemical properties are compared with those of the pristine graphite. The cell performance degrades due to the partial destruction of the graphite structure caused by the introduction of electrochemically inert -PSI group. In contrast, -SI modification basically does not affect the initial charge-discharge coulombic efficiency and reversible capacities of the graphite, but significantly improves the cycling stability of the corresponding lithium-ion cells, nearly doubles the cycle life of the graphite-lithium iron phosphate full-cell. This is because -SI can suppress the destruction of graphite by the solvent, promote the charge transfer of Li+ ions at the electrode surface, and reduce the impedance of the SEI layer and the consumption of active lithium.

Enhanced Thermal Conductivity and Bending Strength of Graphite Flakes/aluminum Composites Via Graphite Surface Modification

The effect of graphite surface modification on the thermal conductivity (TC) and bending strength of graphite flakes /Al composites (Gf/Al) prepared by gas pressure infiltration were investigated. Al3Ni and Al4C3 phase may form at the interface in Ni-coated Gf/Al and uncoated Gf/Al composites, respectively, while the Al-Cu compound cannot be observed in Cu-coated Gf/Al composites. The Cu and Ni coatings enhance TC and the bending strength of the composites in the meantime. TC of Cu-coated Gf/Al composites reach 515 Wm−1·K−1 with 75 vol% Gf, which are higher than that of Ni-coated Gf/Al. Meanwhile, due to Al3Ni at the interface, the bending strength of Ni-coated Gf/Al composites are far more than those of the uncoated and Cu-coated Gf/Al with the same content of Gf. The results indicate that metal-coated Gf can effectively improve the interfacial bonding between Gf and Al.

Surface modification of graphite by ion implantation for promoting the electrochemical property in Li-ion batteries

Nowadays, graphite is still the commercial anode material for Li-ion batteries although many kinds of anode materials have been reported. A great deal of efforts has been devoting to improving the specific gravimetric capacity of graphite by doping or preparing hierarchical structure. However, the volumetric capacity of graphite is not taken seriously compared to the specific gravimetric capacity. In this paper, a surface modification method, ion implantation, has been put forward to improve the volumetric capacity of graphite with high coulombic efficiency. After modification with 50 keV N+ ions at 1 × 1012 ions/cm2, the volumetric capacity of implanted graphite increases 29.6% (696 mAh/cm3) compared to that of pure graphite electrode (537 mAh/cm3) with a super-high initial coulombic efficiency of ~95.9%. Moreover, the influence of nitrogen doping and vacancies induced by N+ ions implantation on the improving of volumetric capacity is discussed. The implanted effects of graphite are also observed by HRTEM, GIXRD, Raman and XPS.

Improved fast charging capability of graphite anodes via amorphous Al2O3 coating for high power lithium ion batteries

Fast charging capability is a high demand feature of lithium ion batteries used in electric vehicles; however, current lithium ion battery technology does not meet electric vehicles fast charging requirements. In this work, it demonstrates that surface modification of graphite using amorphous Al2O3 is an efficient way to improve the fast charging capability of graphite anode materials for lithium ion batteries. Surface-engineered graphite with 1 wt% Al2O3 exhibits a reversible capacity of about 337.1 mAh g−1, even at a high rate of 4000 mA g−1, corresponding to 97.2% of the capacity obtained at a current density of 100 mA g−1. Full cell tests adopting LiCoO2 cathodes and Al2O3-coated graphite anodes confirm that the introduction of amorphous Al2O3 can improve the fast charging capability of graphite anode materials. Wettability tests and electrochemical impedance spectroscopy analysis reveal that this fast charging improvement results from the increased electrolyte wettability on the graphite that is induced by the Al2O3 layer on its surface. Our approach is a practical means to attaining enhanced fast charging capabilities from graphite anode materials for use in high power lithium ion batteries.

Formation of submicron thickness films under processing graphite by proton beam

Modification of graphite surface under irradiation by beam of protons with energy 50 keV was studied. Protons flux was equal 4×1015 and 2×1016 cm−2. It was established that under the proton action the sample surface was converted into a periodic structure in the form of ridges, located in increments of less than 1 μm. The height of ridges was about of 2 μm; their longitudinal size was about of 10 μm. Increase in radiation dose led to a more intensive growth of discovered structures. The transparent thin films were detected on the graphite surface with help of scan electronic microscope. The action of the arc discharge on the modified surface of graphite was described.

Study on graphite surface modification by non-electrode plasma electrolysis

A novel non-electrode plasma electrolysis technique was developed in the paper in order to rapidly prepare a coating on graphite. The coating was mainly composed of SiO2 with the thickness of ~ 7 µm. A small amount of SiC was also detected in the coating. The coating exhibited superior oxidation resistance at 1000 °C in air, evidenced by the visible polishing marks, smooth surface and the much decreased roughness from ~ 120 µm to ~ 50 µm. The simulation of thermal effects was conducted in order to establish the formation mechanism of the coating on graphite. We believe that the novel non-electrode plasma electrolysis technique will find a wide range of applications in preparing high-performance graphite and its composites.

Surface engineering of graphite anode material with black TiO2-x for fast chargeable lithium ion battery

One of the most important challenges in the improvement of the lithium ion battery (LIB) for electric vehicle (EV) applications is its fast charging capability. However, currently used graphite anode materials cannot meet this requirement for EVs. Herein, we demonstrate that surface modification of graphite using oxygen-deficient black titanium oxide (TiO2−x) is an efficient way to improve the fast charging capability of graphite anode material for LIB. The proposed surface engineered anode material, 1 wt% TiO2-x coated graphite anode material, at a high rate of 5 C-rate, exhibited 98.2% of the capacity obtained at a rate of 0.2 C without any degradation of other performances. Full cell tests adopting LiCoO2 as a cathode material with TiO2-x coated graphite anode material also confirmed that the TiO2-x coating layer can improve the fast charging capability of graphite anode material. Such an improvement in the fast charging capability has mainly been attributed to the modified interface between the anode and the electrolyte by surface-engineering of the TiO2-x layer on the surface of graphite. These results show that the approach presented in this work, interfacial engineering of graphite using oxygen deficient TiO2-x, deserves to be regarded as one of the most promising ways to develop an anode material with fast charging capability for high power LIB for EV applications.

Work function modifications of graphite surface via oxygen plasma treatment

The surface modification of graphite by oxygen plasma was investigated experimentally (X-ray diffraction, nanoparticle tracking analysis, laser desorption ionization mass spectrometry, thermogravimetry, water contact angle) and by molecular modelling (Density Functional Theory). Generation of surface functional groups (mainly OHsurf) leads to substantial changes in electrodonor properties and wettability gauged by work function and water contact angle, respectively. The invoked modifications were analyzed in terms of Helmholtz model taking into account the theoretically determined surface dipole moment of graphite—OHsurf system (μ=2.71D) and experimentally measured work function increase (from 0.75 to 1.02eV) to determine the OH surface coverage (from 0.70 to 1.03×1014 groups cm−2). Since the plasma treatment was confined to the surface, the high thermal stability of the graphite material was preserved as revealed by the thermogravimetric analysis. The obtained results provide a suitable quantitative background for tuning the key operating parameters of carbon electrodes: electronic properties, interaction with water and thermal stability.

Thermomechanical Characteristics of Low Carbon Magnesia-Based Monolithic Refractory Containing Nanostructured Surface-Modified Graphites in Matrix

ABSTRACTThis study has been carried out on castable and matrix of a magnesia-based unshaped refractory system containing respectively 5.0% and 20.0% graphites. The graphite has been incorporated either as uncoated or surface-modified form, the latter containing a thin sol-gel calcium aluminate film over graphite surface. Surface modification of graphite has been confirmed by scanning electron microscopy, X-ray diffraction, Raman spectra, Fourier transformed infrared study and some other experiments. The sol-gel coating improved hydrophilicity and oxidation resistance of graphite. Sinterability, thermal and thermomechanical properties of castable matrices have been elaborately documented. From this work it is apparent that presence of coated graphite in matrix part of basic castable is not that encouraging as observed in alumina-carbon system. However, the castable properties as a whole are satisfactory due to protection of graphite and its less water demand for casting.

Micro-orientation control of silicon polymer thin films on graphite surfaces modified by heteroatom doping

Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy is applied to study orientation structures of polydimethylsilane (PDMS) films deposited on heteroatom-doped graphite substrates prepared by ion beam doping. The Si K-edge NEXAFS spectra of PDMS show opposite trends of polarization dependence for non irradiated and N2+-irradiated substrates, and show no polarization dependence for an Ar+-irradiated substrate. Based on a theoretical interpretation of the NEXAFS spectra via first-principles calculations, we clarify that PDMS films have lying, standing, and random orientations on the non irradiated, N2+-irradiated, and Ar+-irradiated substrates, respectively. Furthermore, photoemission electron microscopy indicates that the orientation of a PDMS film can be controlled with microstructures on the order of μm by separating irradiated and non irradiated areas on the graphite surface. These results suggest that surface modification of graphite using ion beam doping is useful for micro-orientation control of organic thin films.

A long life 4 V class lithium-ion polymer battery with liquid-free polymer electrolyte

Abstract Ether-based solid polymer electrolyte (SPE) is one of the most well-known lithium ion conductors. Unlike the other inorganic electrolytes, SPE exhibits advantages of flexibility and large-area production, enabling low cost production of large size batteries. However, because the ether group is oxidized at 4 V versus Li/Li+ cathode, and due to its high irreversibility with the carbon anode, ether-based SPE was believed to be inapplicable to 4 V class lithium-ion batteries with carbon anode. Here we report a remarkably stable SPE in combination with a 4 V class cathode and carbon anode achieved by the proper design at the interface. The introduced boron-based lithium salt prohibits further oxidation of SPE at the cathode interface. The surface modification of graphite by the annealing of polyvinyl chloride mostly prohibits the continuous consumption of lithium at the graphite anode. Using above interface design, we achieved 60% capacity retention after 5400 cycles. The proposed battery provides a possible approach for realizing flammable electrolyte-free lithium-ion batteries, which achieve innovative safety improvements of large format battery systems for stationary use.

Revisiting Surface Modification of Graphite: Dual-Layer Coating for High-Performance Lithium Battery Anode Materials.

Surface modification of electrode active materials has garnered considerable attention as a facile way to meet stringent requirements of advanced lithium-ion batteries. Here, we demonstrated a new coating strategy based on dual layers comprising antimony-doped tin oxide (ATO) nanoparticles and carbon. The ATO nanoparticles are synthesized via a hydrothermal method and act as electronically conductive/electrochemically active materials. The as-synthesized ATO nanoparticles are introduced on natural graphite along with citric acid used as a carbon precursor. After carbonization, the carbon/ATO-decorated natural graphite (c/ATO-NG) is produced. In the (carbon/ATO) dual-layer coating, the ATO nanoparticles coupled with the carbon layer exhibit unprecedented synergistic effects. The resultant c/ATO-NG anode materials display significant improvements in capacity (530 mA h g(-1) ), cycling retention (capacity retention of 98.1 % after 50 cycles at a rate of C/5), and low electrode swelling (volume expansion of 38 % after 100 cycles) which outperform that of typical graphite materials. Furthermore, a full-cell consisting of a c/ATO-NG anode and an LiNi0.5 Mn1.5 O4 cathode presents excellent cycle retention (capacity retention of >80 % after 100 cycles). We envision that the dual-layer coating concept proposed herein opens a new route toward high-performance anode materials for lithium-ion batteries.

Surface modification of graphite and ceramics with metals using induction heating

In order to join metals to graphite or ceramics by soldering or brazing, a new surface modification method using induction heating was developed for graphite and ceramics. Such source metals as Cu, Ni, Cr, etc. were induction-heated in vacuum atmosphere and making deposited films on the deposition substrate, or the target substrate; graphite, AlN, Si3N4. The applicability of this method was investigated and the deposited layer was analysed by SEM observation, Auger electron spectrum analysis, X-ray diffractometry, and EPMA. By comparison of ambient vacuum pressure during deposition and the saturated vaopr pressure of source metals, this method was considered to utilize the sublimation phenomenon.

Novel Surface Modification of Graphite with Excellent Performance for Sodium Ion Battery

Recently, sodium–ion batteries (SIBs) have attracted increasing attention because of the wide availability and relative low cost of sodium, as compared with lithium. In addition, SIBs could possess similar chemical nature to lithium-ion batteries (LIBs). Nevertheless, Na–ion is about 55% larger than the Li–ion, resulting in serious obstruction to obtain high reversibility of Na–ion insertion and extraction during the charging/ discharging process. As a common anodic material for LIBs, graphite is not suitable for SIBs because Na–ion is known to hardly intercalate into graphite. Up to this point, several investigations have demonstrated that the structure and surface modification of carbon materials are significantly related to the capacity and cycling stability of SIBs. For example, hard carbon materials show high capacities of 200–300 mAh/g as anodes for NIBs. Furthermore, nitrogen–doped carbon materials have been developed to provide significant enhancement in capacity, presumably because of increasing reactivity and electronic conductivity. Graphene–based carbon material has also attracted attention because of its high specific surface area and superior conductivity. However, it must be noted that graphene–based carbon materials possess low volumetric capacity owing to low tap density (< 0.02 g/cm3), which comes from large amounts of hydrogen or significant nanoporosity. Overall, to date, there has not been report on high capacity and good cycling stability of carbon material for SIBs at high temperatures. It has been known that several alkali atoms, including Li, K, Rb and Cs, can readily form intercalation compounds with graphite. Contrary to the heavy alkali metals, the intercalation of Na into graphite is known to be difficult. Therefore, ionic size is not the major effect that precludes the intercalation of Na ion. In this study, we report modified graphite by partial oxidation of graphite flakes to introduce oxygen-containing functional groups, such as hydroxyl, carboxyl, and ether groups, randomly into the layered graphene matrix.Compared with graphite, the partially oxidized graphite (POG) has an expanded interlayer distance and thus an enhanced micropores and nanometer channels, facilitating Na-ion diffusion. Meanwhile, the presence of oxygen atoms within the graphite structure is shown to remarkably enhance Na-ion intercalation capacity. The un-oxidized portion of the graphite maintains high crystallinity and provides bulk electronic conductivity. The other purpose of this report is to improve the surface conductivity of POG and to simultaneously maintain the expanded interlayer distance by introducing conducting polymer, poly(3,4-ethylene-dioxythiophene) (PEDOT) doped with poly(styrenesulfonate) (PSS). The PEDOT-PSS conducting polymer is commercially available in aqueous dispersion, which can easily be casted into film electrode at low temperatures (<100 oC). PEDOT:PSS provides high electric conductivity (ca. 550 S cm-1) and the films can be heated in air at 100 oC for over several hours with only few change in its conductivity. It has been widely used as an antistatic coating material, and as a hole-transport electrode for rechargeable polymer batteries or optoelectronic devices. For application of an anode of SIBs, this novel POG electrode provides a high reversible capacity of 344 mAh/g (Fig. 1) and retains 77.1% after 2000 cycles at room temperature in NaPF6/EC/DEC (Fig. 2a) and 70.3% after 1000 cycles in NaPF6/EC/PC (Fig. 2b). It is found that the PEDOT:PSS film can prevent the co-intercalation of solvent into the graphite layer even in EC/PC solvent. The crystalline structures of the POG materials have been characterized in detail by high-resolution TEM as well as in situ synchrotron XRD.