Graphite Intercalated Compound Research Articles

Optimizing the performance of a graphite anode for innovative metal-ion batteries and hybrid capacitors

Herein, we present an optimum method for maximizing the electrochemical performance of graphite anodes using two heat treatment methods involving graphite intercalated compound (GIC) group within graphite, namely, thermal shock (TS; directly input target temperature) and gradual heating (GH; including ramping time). Different heating methods for preparing expanded graphite (EG) involve different reactions, relaxation times, and diffusion pathways for the diffusion of metal ions into EG. We find that rapidly shocking the layered structure can facilitate faster lithium and potassium ion diffusion from EG (TS) (heated for 30 min) via different intercalation/deintercalation processes compared to that from EG (GH). Consequently, EG (TS) exhibits the most significantly improved electrochemical performance among the lithium and potassium ion half-cells. For full lithium-ion hybrid capacitors (LIHCs), EG (TS)||activated carbon (AC) shows reasonable values of maximum power density (2.8 kW kg−1 with 59.12 Wh kg−1) and energy density (196.41 Wh kg−1), demonstrating its ultrahigh durability (capacity retention: 70.01%) over 12000 cycles at 2.0 A g−1. In addition, for potassium-ion hybrid capacitors (PIHCs), reasonable performance is achieved (average capacity of 82.02 mAh g−1 at 1.0 A g−1 over 2000 cycles with 94.35% capacity retention), demonstrating the high efficiency of PIHCs for substituting LIHCs without any systematic alterations.

Comparison of perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA) and perfluorobutane sulfonate (PFBS) removal in a combined adsorption and electrochemical oxidation process

This study focused on three of the most studied PFAS molecules, namely perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA) and perfluorobutane sulfonate (PFBS). They were compared in terms of their adsorption capacity onto graphite intercalated compound (GIC), a low surface area, highly conductive and cheap adsorbent. The adsorption on GIC followed a pseudo second order kinetics and the maximum adsorption capacity using Langmuir was 53.9 μg/g for PFOS, 22.3 μg/g for PFOA and 0.985 μg/g for PFBS due to electrostatic attraction and hydrophobic interactions. GIC was added into an electrochemical oxidation reactor and >100 μg/L PFOS was found to be fully degraded (<10 ng/L) leaving degradation by-products such as PFHpS, PFHxS, PFPeS, PFBS, PFOA, PFHxA and PFBA below 100 ng/L after 5 cycles of adsorption onto GIC for 20 min followed by regeneration at 28 mA/cm2 for 10 min. PFBS was completely removed due to degradation by aqueous electrons on GIC flakes. Up to 98 % PFOA was removed by the process after 3 cycles of adsorption onto GIC for 20 min followed by regeneration at 25 mA/cm2 for 10 min. When PFBS was spiked individually, only 17 % was removed due to poor adsorption on GIC. There was a drop of 3–40 % by treating PFOS, PFOA and smaller sulfonates in a real water matrix under the same electrochemical conditions (20 mA/cm2), but PFOS and PFOA removal percentage were 95 and 68 % after 20 min at 20 mA/cm2.

Combined adsorption and electrochemical oxidation of perfluorooctanoic acid (PFOA) using graphite intercalated compound

Perfluorooctanoic acid (PFOA) is a bioaccumulative synthetic chemical containing strong C–F bonds and is one of the most common per- and polyfluoroalkyl substances (PFAS) detected in the environment. Graphite intercalated compound (GIC) flakes were used to adsorb and degrade PFOA through electrochemical oxidation. The adsorption followed the Langmuir model with a loading capacity of 2.6 µg PFOA g−1 GIC and a second-order kinetics (3.354 g µg−1 min−1). 99.4% of PFOA was removed by the process with a half-life of 15 min. When PFOA molecules broke down, they released various by-products, such as short-chain perfluoro carboxylic acids like PFHpA, PFHxA, and PFBA. This breakdown indicates the cleavage of the perfluorocarbon chain and the release of CF2 units, suggesting a transformation or degradation of the original compound into these smaller acids. Shorter-chain perfluorinated compounds had slower degradation rates compared to longer-chain ones. Combining these two methods (adsorption and in situ electrochemical oxidation) was found to be advantageous because adsorption can initially concentrate the PFOA molecules, making it easier for the electrochemical process to target and degrade them. The electrochemical process can potentially break down or transform the PFAS compounds into less harmful substances through oxidation or other reactions.

Adsorption of PFOS onto graphite intercalated compound and analysis of degradation by-products during electro-chemical oxidation

Perfluorooctane sulfonate (PFOS) is a highly recalcitrant perfluoro chemical belonging to the family of per- and polyfluoroalkyl substances (PFAS). Its adsorption and degradation was demonstrated in a novel PFAS remediation process involving the adsorption onto graphite intercalated compounds (GIC) and the electrochemical oxidation. The Langmuir type of adsorption was characterized by a loading capacity of 53.9 μg PFOS g−1 GIC and a second order kinetics (0.021 g μg−1 min−1). Up to 99% of PFOS was degraded in the process with a half-life of 15 min. The breakdown by-products included short chain perfluoroalkane sulfonates such as Perfluoroheptanesulfonate (PFHpS), Perfluorohexanesulfonate (PFHxS), Perfluoropentanesulfonate (PFPeS) and Perfluorobutanesulfonate (PFBS), but also short chain perfluoro carboxylic acids such as perfluorooctanoic acid (PFOA), perfluorohexanoic acid (PFHxA) and perfluorobutanoic acid (PFBA) indicating different degradation pathways. These by-products could also be broken down but the shorter the chain the slower the degradation rate. This novel combined adsorption and electrochemical process offers an alternative treatment for PFAS contaminated waters.

Facile fabrication of freestanding graphene nanoplatelets composite electrodes for multi battery storage

Graphene electrode offers an exceptional high energy storage capacity in various electrochemical systems, but the practical applications of graphene electrodes in ion storage devices are hindered by high processing cost for a high crystallinity graphene. Thanks to the redox-amphoteric attributes of graphene, acceptor-type graphite intercalated compound (GICs) are receiving great interest for novel battery systems. Herein, freestanding, highly conductive, porous graphene nanoplates film (GNPF) are prepared by a facile, one step phase inversion approach. The GNPF electrodes present an excellent electrochemical performance in aluminium ion battery (AIB) with a high areal loading of 4.14 mg cm−2 delivers a remarkable specific capacity of 83 mAh g −1 (translated to 0.35 mA cm−2) at 1 A g −1 after 2000 cycles. The porous GNPF electrodes endows high voltage storage in a dual carbon battery (DCB) system. The battery presents superior cycling stability at high cut-off voltage of 5.0 V with a reversible capacity of 50 mAh g−1 after 100 cycles at 50 mA g−1. The current approach simplifies the fabrication of freestanding graphene-based electrodes while maintaining the electrochemical activity and structural stability of GNPs for high electrochemical energy storage applications.

The effect of graphite intercalated compound particle size and exfoliation temperature on porosity and macromolecular diffusion in expanded graphite

The pore structure of expanded graphite (EG) including pore volume, pore size distribution and surface area is investigated by mercury porosimetry, nitrogen adsorption and SEM. Also, the diffusion of silicone oil molecules as macromolecules with different molecular weights into EG pores is studied. Various EG samples were prepared by the sudden heating of graphite intercalated compound (GIC) with varying particle size of 35, 50, 80 and 200 meshes in an electrical furnace at temperatures of 700, 800 and 900 °C. The EGs were characterized by FTIR to evaluate the presence of functional groups. It was found that the exfoliation process has not significantly introduced oxygen functional groups such as epoxy and carboxyl groups to the EG structure. Therefore the chemical structure of the EG is very close to pristine graphite. The mercury porosimetry results showed a broad range of total pore area from 5 to 31 m2/g for the EGs. The particle size of GIC and exfoliation temperature showed strong effects on the pore size of EG. The mercury intrusion porosimetry and nitrogen adsorption isotherms revealed that μm-pores are dominant as compared with nm-pores in all EG samples. The diffusion of silicone oils as macromolecular guests with three different viscosities was experimentally studied to analyze the diffusion facts of EG as the host. It was observed that as the exfoliation temperature decreases, the sorption capacity decreases; and EG samples prepared from the GICs with smaller particle size have lower sorption capacity. Sorption experiments also showed that the whole pore volume of EG is not filled with silicone oil leading to this fact that EG includes relatively closed pores. A new model was suggested for the sorption capacity of EG as a function of the pore area of EG and the square root of molecular weight of silicone oil.

A novel electrically conductive water borne epoxy nanocomposite coating based on graphene: facile method and high efficient graphene dispersion

In this work, we present a novel method to exfoliate graphite to graphene oxide nanosheets with single to 3 layers at concentration as high as 15 mg/ml. In the first step, graphite intercalated compound (GIC) was obtained through a chemical intercalation process. In the next step, GIC was expanded and used as the precursor to obtain oxidized graphite. Oxidized graphite was introduced into a high alkaline medium and a high-speed homogenizer was used to complete the exfoliation process. Raman spectroscopy, XPS, XRD, TGA, SEM and TEM were used to characterize the synthesized graphene oxide nanosheets. Electrically conductive coatings were prepared by adding and stirring graphene oxide dispersion into an epoxy-hardener pre-mixture. The prepared coatings were post cured at 100 °C followed by annealing at 225 °C to in situ reduce the incorporated graphene oxide to graphene nanosheets. High electrical conductivity values as 0.5 S/m was obtained for the epoxy-graphene nanocomposite at graphene loading level of 1.5 wt%, which is comparable to previously reported data using more complex and laborious fabrication methods. Cryo-SEM images were captured in the liquid phase to investigate electrical network formation in the polymeric matrix.

Properties of Stretchable Graphite Intercalation Compound/Polydimethylsiloxane Composites after Cyclic Tensile Strain of 20%

The expanded graphite intercalated compound (GIC)/poly(dimethyl siloxane) (PDMS) composites were pre- pared and the effects of cyclic stretching on the morphology, thermal conductivity and surface resistance of the com- posites were investigated. PDMS resin did not penetrate into the pores of the expanded GIC. The uniform distribution and spatially connected GICs in the PDMS matrix resulted in improved thermal conductivity and decreased sheet resis- tance. The thermal conductivity and sheet resistance of GIC(20 wt%)/PDMS composites were changed after 1000 cycles of 20% tensile strain from 0.80 W/mK and 6×10 Ω/sq to 0.69 W/mK and 3.04×10 Ω/sq, respectively. The decreased thermal conductivity and the increased sheet resistance of the composites after cyclic stretching was attributed to the for- mation of the interfacial crack between PDMS matrix and the GIC filler.

Challenging the nature of low-energy plasmon excitations in CaC6 using electron energy-loss spectroscopy

The nature of low-energy plasmon excitations plays an important role in understanding the low-energy electronic properties and coupling mechanism of different superconducting compounds such as CaC. Recent ab initio studies predict a charge carrier intraband plasmon in keeping with a low-energy acoustic plasmon. Here, we have studied the low-energy electronic excitations of CaC using high-resolution electron energy-loss spectroscopy in transmission at low temperatures. The analysis of the core level excitations leads to the conclusion that hybridization between graphite and calcium states plays an essential role in this graphite-intercalated compound. Regarding the low-energy plasmon excitation, we observe the formation of an intraband (charge carrier) plasmon with a negative dispersion at about 3.5 eV in sound agreement with the theory. Finally, a weak excitation around 1.2 eV with an almost linear dispersion relation can be observed as predicted for an acoustic plasmon that may mediate the superconducting coupling in CaC. However its optical limit at 1 eV challenges the theoretical predictions and safely rules out an electronic superconducting coupling mechanism in CaC

Low-energy plasmonic structure in CaC6

The low-energy dielectric properties of CaC${}_{6}$---a representative graphite intercalated compound (GIC)---were investigated by $\mathit{ab}$ $\mathit{initio}$ time-dependent density functional theory calculations with full inclusion of local field effects. The calculations predict the existence of several kinds of plasmons in CaC${}_{6}$ with energy below 10 eV. The mode with the largest energy is a conventional $``\ensuremath{\pi}p$'' mode strongly dispersing in the hexagonal basal plane and almost nondispersing in the perpendicular direction. In the 2.3--3 eV energy range, we find a long-lived intraband plasmon with negative (positive) dispersion with momentum transfer in (perpendicular to) the basal plane. In the 0--1.5 eV energy range, a mode with linear soundlike dispersion along all three high-symmetry directions is observed. All the three modes present strong anisotropy originated from the band structure. The physical origin of these excitation modes is discussed in terms of intra- and interband transitions. The crucial role of local field effects in the propagation of the two lowest-energy modes at large momentum transfers and in the determination of its dispersion over extended momentum-transfer region is analyzed.

Thermal diffusivity of in-situ exfoliated graphite intercalated compound/polyamide and graphite/polyamide composites

The thermal diffusivity of graphite intercalated compound (GIC)/polyamides (PA6, PA66 and PA12) and graphite/polyamides composites were investigated. The polyamides/GIC composites were prepared by an in-situ exfolia- tion melting process and thermal diffusivity of the composites was measured by a laser flash method. The surface chemistry of the GIC and graphite was investigated using Fourier transform infrared spectroscopy, the fracture morphology of the composites was observed by field emission scanning electron microscopy. The thermal diffusivity of the in-situ exfoliation processed PA/GIC composites showed a significant improvement over those of PA/expanded graphite intercalated com- pound composites and PA/graphite composites. We suggest that the larger flake size and high expansion ratio of the GIC during the in-situ exfoliation process leads to 3-dimensional conductive pathways and high thermal diffusivity. Thermal diffusivity of the polyamides/GIC (20 vol%) composites was increased approximately 18 times compared to that of pure polyamides.

Magnetic properties of cobalt‐carbon nanocomposites

AbstractThe paper presents the results of experimental study of the structure and magnetic characteristics of Co‐graphite compounds, which were obtained by metal reduction of metal chlorides in graphite intercalated compound (GIC) by C8K. The obtained materials were shown to have heterogeneous structure consisting of nanographite matrix in which nanoclusters of Co‐GIC are distributed. Magnetic field was applied either along or perpendicularly to the C‐axis. It was shown that magnetism of this compound is determined mainly by nanoclusters of Co‐GIC for which high anisotropy of magnetic characteristic were observed. ZFC and FC temperature dependences of magnetic susceptibility indicate the formation spin glass state below ∼20 K. It was also shown that experimental dependences of magnetization contain the contribution due to antiferromagnetic sublattice and magnetizationdue to uncompensated magnetic moments (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

High-pressure behavior ofCsC8graphite intercalation compound: Lattice structures and phase-transition mechanism

The high pressure phase diagram of CsC8 graphite intercalated compound has been investigated at ambient temperature up to 32 GPa. Combining X-ray and neutron diffraction, Raman and X- ray absorption spectroscopies, we report for the first time that CsC8, when pressurized, undergoes phase transitions around 2.0, 4.8 and 8 GPa. Possible candidate lattice structures and the transition mechanism involved are proposed. We show that the observed transitions involve the structural re- arrangement in the Cs sub-network while the distance between the graphitic layers is continuously reduced at least up to 8.9 GPa. Around 8 GPa, important modifications of signatures of the electronic structure measured by Raman and X-ray absorption spectroscopies evidence the onset of a new transition.

Preparation of interfacially compatibilized PP‐EPDM thermoplastic vulcanizate/graphite nanocomposites: Effects of graphite microstructure upon morphology, electrical conductivity, and melt rheology

AbstractElectrically conductive PP/EPDM dynamically crosslinked thermoplastic vulcanizate (TPV)/expanded graphite (EG) has been successfully prepared via melt compounding of maleic anhydride grafted polypropylene (PP‐g‐MA)/EG masterbatch and a commercially available TPV material. Correlation between graphite microstructure, and electrical conductivity as well as melt rheological behavior has been studied. Natural graphite flake (NGF), graphite intercalated compound (GIC), and exfoliated graphite (EG) have been employed and compared. Scanning electron microscopy (SEM) showed the presence of 100–200 nm nanolayers in the structure of PP‐g/EG masterbatches, whereas thinner platelets (1.5–2.5 nm) were revealed by transmission electron microscopy (TEM). Better dispersion of the graphite nanolayers in the microstructure of TPV/PP‐g‐MA/EG composite was verified, as the 7.3 Å spacing between the aggregated graphite nanolayers could not be observed in the XRD pattern of this material. TPV/PP‐g/EG nanocomposites exhibited much lower conductivity percolation threshold (φc) with increased conductivity to 10−5 S/cm at EG wt % of 10. Higher nonlinear and nonterminal melt rheological characteristics of dynamic elastic modulus (G′) at low frequency region was presented by the TPV/PP‐g/EG nanocomposites, indicating the formation of nanoscopic conducting multiple networks throughout the continuous TPV matrix. Maleated PP was found to be much more effective in separating EG nanolayers which is attributed to the higher interfacial interaction between PP‐g‐MAH and EG, synergized with its multiporous structure. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Study on thermal behaviors of Li/H atom in the bulk graphite by molecular dynamics method

A system with periodical structure of graphite, in which a Li or H atom is set in the center of the supercell, has been simulated by molecular dynamics method to study the thermal diffusion of Li and H in the bulk graphite. It is found that the rates of diffusion of both Li and H atoms increase with the increase of the simulation temperature: from 50 K to 200 K, and the specific diffusive rates and behaviors for Li and H are different according to their trajectories. The diffusive curves for Li can be classified into three types, while H has only one type of diffusive curve, which shows that the interaction between Li and carbon is weaker than that between H and carbon. The conductive band gap of graphite is also calculated by the extended Huckel method. The gap is broadened by about 0.1 eV when graphite is intercalated with H, but the gap remains unchanged when graphite is intercalated with Li. It indicates that the addition of Li does not influence the conduction characteristic of graphite while that of H does. Thus Li-GIC (Graphite Intercalated Compound) is proposed to be a favorable material for the electrode.

Microwave losses of bulk CaC6

We report a study of the temperature dependence of the surface resistance RS in the graphite intercalated compound (GIC) CaC6, where superconductivity at 11.5K was recently discovered. Experiments are carried out using a copper dielectrically loaded cavity operating at 7GHz in a “hot finger” configuration. Bulk CaC6 samples have been synthesized from highly oriented pyrolytic graphite. Microwave data allow to extract unique information on the quasiparticle density and on the nature of pairing in superconductors. The analysis of RS(T) confirms our recent experimental findings that CaC6 behaves as a weakly-coupled, fully gapped, superconductor.

Thermal behavior of hydrogen atom intercalated between two layers of C 150H 30 graphite plane: MD simulation

For investigation of thermal behaviors of hydrogen (H) atom in a graphite intercalated compound (GIC), the molecular dynamic (MD) procedure at the molecular mechanics 2 (MM2) level was applied to a hydrogen terminated cluster model composed of two layers of C 150H 30 plane. On the basis of the optimized structure, one intercalated H atom was stabilized at the mass center of the cluster model. According to the trajectory of the intercalated H atom, the diffusion is initiated at 100 K towards lower potential energy area in the periphery of the cluster model. The diffusion rate increased with the increase in the simulation temperature from 100 to 500 K. According to the extended Hückel calculation, the band gap of graphite is broadened by 0.1 eV with the intercalation. Thus, the present MD simulation proposed that the semiconductivity of GIC is promoted due to the development of the ionic conductivity. However, H atom adsorbed on the surface of C 150H 30 plane formed the stable covalent bond with a host carbon atom and made little contribution to the conductivity.

Electrical resistivity in the c-axis direction of the ZnCl 2 graphite intercalation acceptor compound

The c-axis electrical resistivity of the stage-4 acceptor ZnCl 2 graphite intercalated compound (GIC) has been measured in the temperature range (4.2–300)K. The obtained values are larger than those of Highly Oriented Pyrolytic Graphite (HOPG). Evidence for a change in the observed metallic tendency at 97K and a possible order-disorder transition at about 187K are also presented. According to a model by Sugihara, the conduction mechanism is a hopping process activated by phonons and impurities. In our sample, the activation by impurities is predominant over the whole temperature range.

Low-temperature structure of a HNO3-graphite intercalated compound: A neutron-diffraction study.

Neutron diffractions were performed on a sample of a fourth-stage ${\mathrm{HNO}}_{3}$-graphite intercalation compound at room temperature and at low temperature. This compound is known to undergo a crystallographic transformation at approximately 250 K from its known room-temperature structure, which belongs to the space group R3\ifmmode\bar\else\textasciimacron\fi{}m, (${D}_{3d}^{5}$), to an unknown low-temperature structure. The observed neutron diffractions and calculated structure factors are studied and the low-temperature structure is determined. It is found that the structure is trigonal and belongs to the space group P${3}_{1}$21 (${D}_{3}^{4}$). .AE

Phase transition in AlCl3-graphite as seen by the thermal hysteresis in the conduction-carrier spin resonance.

A phase transition at 168 K has been recognized from the thermal hysteresis of the conduction-carrier spin-resonance parameters in the stage-7 acceptor ${\mathrm{AlCl}}_{3}$-graphite intercalated compound (GIC). Below the transition temperature, the final low-temperature in-plane residual resistivity of the sample was found to be dependent on its previous thermal history. Paradoxically, quenching effects, contrary to previous reports on low-stage acceptor GIC's, leave the system in an ``orderedlike'' state of higher in-plane conductivity.