Untersuchungen zum Mechanismus der Intercalation von Antimonpentachlorid in das Graphitgitter

Studies on the Mechanism of the Antimony Pentachloride Intercalation in Graphite The SbCl₅ intercalation in graphite in liquid media (immersion in SbCl₅ and in SbCl₅/CCl₄-mixtures, respectively) reveals an induction period ranging from 0,25 up to 8 hours. Graphite intercalation by liquid SbCl₄F, SbCl₂F₃ and SbF₅ does not exhibit any induction period. The induction time of synthetic graphites is shorter than that of natural graphites. The decrease of graphite particle sizes as well as the increase of SbCl₅ concentration in CCl₄ solution and the presence of co-reagents (e.g. SbCl₃) reduce the induction time. Increasing the SbCl₅ concentration in CCl₄, an increase of SbCl₅ quantity in graphite and of identity period along c-axis in stage 2 have been found. Gase phase intercalation of SbCl₅ is a reaction of successive lowering of the stage index without any induction period. Using EPMA investigations it have been stated that nucleation at the prismatic edges (opening of galleries) controls the intercalation kinetics. An explanation of induction period and ?autocatalytic”? reaction after the induction period is given on basis of interaction of electrostatic forces, connected with adsorption of guest molecules, and elastic forces, resulting from dilatation during intercalation. Formation of complexes between SbCl₅ and co-reagents (e. g. SbCl₃) strengthens the electrostatic effect.     

Reaction of Graphite with Sulfuric Acid in the Presence of KMnO<Subscript>4</Subscript>

The reaction of graphite with sulfuric acid in the presence of KMnO₄ (oxidant : graphite ratio 0.027–0.55) involves consecutive and concurrent reactions: graphite intercalation and direct oxidation of the carbon matrix. The properties of graphite bisulfate and its reaction products are determined by the stage number of the intercalation compound; the decomposition enthalpies of the stage I–IV graphite bisulfate correlate with the enthalpies of graphite intercalation with sulfuric acid.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 2, 2005, pp. 184–191.Original Russian Text Copyright © 2005 by Sorokina, Khaskov, Avdeev, Nikol’skaya.     

Über die Reversibilität der elektrochemischen Graphitoxydation in Säuren

On the Reversibility of the Electrochemical Oxidation of Graphite in Acids The oxidation of graphite foil in acids stable to oxidation with varying H₂O content is investigated by cyclic voltammetry and by following the potential curves of graphite electrodes during quantitative galvanostatic electrolyses. It is shown, that e. g. in 70% HClO₄ a graphite oxide is formed with almost 100% current yield, the degree of oxidation of which is essentially lower then for chemically oxidized products. The reaction can be reversed with very good current and material yield and be repeated; the reversibility with reference to the balance of energy decreases with increasing H₂O-content of the acid.     

Graphites from the Zavalie deposit as active materials for lithium-ion batteries

We study the utility of standard graphites (GAK-2, GL-1, EUZ-M, and others) produced by the Zavalie Integrated Graphite Plant (ZGP) as active materials in lithium-ion batteries (LIBs). The structure and main electrochemical characteristics of these graphites are studied for choosing the best type of graphite and evaluating its utility for LIB production. The electrochemical characteristics of the best ZGP graphites and graphite for batteries produced by Superior Graphite Co. (USA), a worldwide leader of the graphite industry, are compared. Some tendencies in the effect of the structure and particle-size distribution on the electrochemical characteristics of graphite electrodes are determined. EUZ-M graphite modified by tin with amorphous carbon is prepared. The reversible capacity of this graphite in the cell against LiCoO₂ exceeds 400 mA h/g. The increased reversible capacity is due to the contribution of components having higher specific parameters; the cycling stability is due to the core-shell structure.     

Facile preparation of graphite intercalation compounds in alkali solution

Graphite intercalation compounds are often prepared by flake graphite, oxidants, inorganic acids, organic acids and intercalated ions which are usually hydrogen protons between the graphene planes. They are also known as the acid-treated graphite intercalation compounds. In this work, alkaline graphite intercalation compounds were prepared by flake graphite, K₂Cr₂O₇, concentrated H₂SO₄ and NaOH, and the morphology and structure were characterized by Electron microscopy and X-ray techniques. The results display that the combination of neutralisation heat and oxidation capability produced by K₂Cr₂O₇ can break the bonds to produce the spaces between the graphene planes and hydroxyl ions also intercalate into the graphene planes to form alkaline graphite intercalation compounds in alkali solution. The morphology and structure of alkaline graphite intercalation compounds are analogous to the ones of the acid-treated graphite intercalation compounds, but the intercalated ions and the expansion volume are different. The results show that the method is an innovation.     

Synthesis,structure and properties of fluorinated graphite

Fluorine-graphite intercalation compounds, C₂F to C₁₆F were synthesized by various methods. C-F bonds range from ionic to semi-covalent. These properties of C-F bonding give to fluorinated graphite metallic conductivity, higher hydrophilicity than graphite and high reduction potential. The c-axis and in-plane structures are governed by C-F bonding, fluorine intercalation rate and host graphites.     

Understanding High‐Rate K+‐Solvent Co‐Intercalation in Natural Graphite for Potassium‐Ion Batteries

Graphite shows great potential as an anode material for rechargeable metal‐ion batteries because of its high abundance and low cost. However, the electrochemical performance of graphite anode materials for rechargeable potassium‐ion batteries needs to be further improved. Reported herein is a natural graphite with superior rate performance and cycling stability obtained through a unique K⁺‐solvent co‐intercalation mechanism in a 1 m KCF₃SO₃ diethylene glycol dimethyl ether electrolyte. The co‐intercalation mechanism was demonstrated by ex situ Fourier transform infrared spectroscopy and in situ X‐ray diffraction. Moreover, the structure of the [K‐solvent]⁺ complexes intercalated with the graphite and the conditions for reversible K⁺‐solvent co‐intercalation into graphite are proposed based on the experimental results and first‐principles calculations. This work provides important insights into the design of natural graphite for high‐performance rechargeable potassium‐ion batteries.     

Study of intercalation of BrF5 in graphite

Conclusions In the formation of intercalation compounds of graphite with BrF₅, the intercalation reaction rate significantly exceeds the reaction rate of fluorination of the graphite lattice. The stage nature of the reaction of intercalation of BrF₅ in graphite was demonstrated.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 953–957, May, 1988.     

超声辅助Hummers法制备氧化石墨烯

采用超声辅助Hummers法制备氧化石墨烯,单片层厚～1 nm。本法首先在Hummers法的低温、中温反应阶段加入超声振荡,以此来分别提高石墨的插层效率和氧化程度,然后在高温反应开始时,采用把含有残留浓硫酸的混合液缓慢滴入低温去离子水中再加热的方式,以此减少硫酸分子等插入物因为局部温度过高从石墨层间脱出,最后通过低速离心得到氧化石墨。使用超声辅助Hummers法制备氧化石墨烯既方便快捷,又能有效地增大氧化石墨的层间距,且随着超声功率的提高,所得氧化石墨的层间距呈扩大趋势。     

In situ X‐ray Diffraction Studies of Cation and Anion Inter­calation into Graphitic Carbons for Electrochemical Energy Storage Applications

Graphite is a redox‐amphoteric intercalation host and thus capable to incorporate various types of cations and anions between its planar graphene sheets to form so‐called donor‐type or acceptor‐type graphite intercalation compounds (GICs) by electrochemical intercalation at specific potentials. While the LiC_x/C_x donor‐type redox couple is the major active compound for state‐of‐the‐art negative electrodes in lithium‐ion batteries, acceptor‐type GICs were proposed for positive electrodes in the “dual‐ion” and “dual‐graphite” cell, another type of electrochemical energy storage system. In this contribution, we analyze the electrochemical intercalation of different anions, such as bis(trifluoromethanesulfonyl) imide or hexafluorophosphate, into graphitic carbons by means of in situ X‐ray diffraction (XRD). In general, the characterization of battery electrode materials by in situ XRD is an important technique to study structural and compositional changes upon insertion and de‐insertion processes during charge/discharge cycling. We discuss anion (X^–) and cation (M⁺) intercalation/de‐intercalation into graphites on a comparative basis with respect to the M_x⁺C_n^– and C_n⁺X_n^– stoichiometry, discharge capacity, the intercalant gallery height/gallery expansion and the M–M or X–X in‐plane distances.     

New salts of graphite,C12+HF2− & C24+SiF5− and the treshold for the oxidative intercalation of graphite

Third row transition metal hexafluorides (MF₆) for which the electron affinity exceeds 130 kcal/mole (M = Os, Ir, Pt) have been found to intercalate graphite with electron oxidation of the host lattice, whereas those with inferior electron affinities (M = W, Re) do not intercalate¹. This behavior can be rationalized on kinetic or thermodynamic grounds; arguing for the latter, a simple Born-Haber cycle may be used which suggests an electron affinity threshold of 120–130 kcal/mole for the MF₆ intercalation reaction. For the general case of intercalation reactions by metal fluorides (with or without added fluorine), wherein the graphite lattice is oxidized, the threshold is determined by the free energy of the half-reaction which produces the intercalating fluoro-anion. The lattice energy of the graphite salt must also be taken into account when comparing free energy thresholds for large (e.g., MF₆) and small (e.g. HF₂^?) intercalating species.We have evaluated the free energy of formation of a number of fluoro-anions from the heats of formation and lattice energies of salts which contain them. These studies indicate a threshold free energy of ca. 110 kcal/mole for graphite intercalation. Two ‘borderline’ second stage compounds, C₂₄⁺SiF₅^? and C₁₂⁺HF₂^?, have been synthesized.     

Formation of nanocomposites of styrene and its copolymers using graphite as the nanomaterial

Graphite‐polymer nanocomposites were prepared by melt blending of various graphites (virgin graphite, expandable graphites, and expanded graphite) with polystyrene and its copolymers (acrylonitrile‐butadiene‐styrene (ABS) and high‐impact polystyrene (HIPS)). Nanocomposites were characterized by X‐ray diffraction, cone calorimetry, thermogravimetric analysis and evaluation of mechanical properties. Nanocomposite formation occurs at higher loadings (3–5%) of expandable graphites but not for virgin or expanded graphite. Copyright © 2005 John Wiley & Sons, Ltd.     

Fluorination of treated carbon

Graphite fluoride is classified into (C₂F)n and (CF)n types from the structure and composition. Both compounds have such unique physicochemical properties as low surface energy, solid lubricating characteristics, and oxidizing ability. However, a long reaction time is required to completely fluorinate graphite and moreover, the decomposition reaction of the product causes the lowering of the yields.In this paper, the effect of the pretreatments of the starting material on the fluorination will be reported on the following methods.1) Fluorination of Exfoliated Graphite Obtained by Heat-treatment of Graphite Lamellar Compound.The exfoliated graphite was obtained by the immersion of graphite into the mixed solution of sulfuric acid and hydrogen peroxide and subsequent heat-treatment. It has both much large surface area and larger lattice strain than that of the original graphite.The exfoliated graphite was much faster fluorinated than the original graphite. The dissociation of fluorine molecules to atoms was found to be a rate-determining step in the formation of graphite fluoride from the exfoliated graphite, whereas the process of diffusion of fluorine molecules was the rate-determining step in the fluorination of the original graphite.2) Fluorination of Residual Carbon Formed upon Pyrolysis of Graphite Fluoride.Graphite fluoride decomposes to carbon and some perfluorocarbons of low molecular weight at high temperature above 600 °C. The residual carbon was amorphous in analogy with petroleum coke or carbon black, but had smaller interlayer spacing and larger specific surface area due to its microporous structure than these amorphous carbonsThe rate of the direct fluorination of residual carbon at a room temperature was comparable to that of active carbon, and the graphite fluoride obtained from the residual carbon has a similar high thermostability to that of graphite fluoride obtained from graphite at a high temperature under an atmosphere of fluorine gas. Upon direct fluorination of the residual carbon a more crystalline graphite fluoride was obtained even at a low temperature than the case of petroleum coke and carbon black. It is interesting that the fluorination of the residual carbon leads to the formation of crystalline graphite fluoride in high yield.     

Estimate of polarization components in oxygen reduction process on expanded natural graphites and acetylene carbon black in acid and alkaline electrolytes

The polarization curves of oxygen reduction in gas diffusion electrodes of expanded natural graphites (ENG, prepared from graphite intercalation compounds synthesized by intercalation of sulfuric and nitric acids into natural graphites GAK-3 and GT-1) and acetylene carbon black in acid (pH 0.6) and alkaline (3 M KOH) electrolytes were analyzed. The transfer coefficients and oxygen reduction exchange currents on ENG and acetylene carbon black were estimated. The experimental polarization curves were described well with the derived semi-empirical equations.     

Über die Einlagerung von Antimonfluoridchloriden in Graphit Versuche zur Darstellung von Metallfluorid-Graphitverbindungen

The reaction between graphite and SbF₃ in Cl₂ atmosphere or SbF₃Cl₂in inert atmosphere gives antimony fluoride-chloride graphite compounds. The first intercalation stage is deep blue and contains 67–68% SbF_xCl_y. The ideal composition is near [C₂₇]_GrSbF₃Cl₂ · 2 SbF₃Cl₂. SbF₃Cl₂ can be substituted partly by SbF₃ or SbF₅. The layer distance decreases with increasing F:Cl ratio from 8.87 to 8.36 Å. There exist also a second and third intercalation stage.     

Graphit-hexachloroplatinat(IV) und Platin(IV)-chlorid-Graphit. Übergang eines Graphitsalzes in eine Metallchlorid-Graphitverbindung

Graphite hexachloro-platinate(IV) and platinum(IV) chloride graphite. Transition of a graphite salt into a metal chloride-graphite compound Whereas graphite does not react with PtCl₄ in Cl₂ atmosphere up to 350°C, with H₂PtCl₆ · xH₂O at 150°C graphite hexachloroplatinate (third intercalation stage) is obtained. The thermal decomposition of the graphite salt gives PtCl₄-graphite with the composition near [C₄₂]_Gr · PtCl_4,3.     

Electrochemical Synthesis of Co-intercalation Compounds in the Graphite-H<Subscript>2</Subscript>SO<Subscript>4</Subscript>-H<Subscript>3</Subscript>PO<Subscript>4</Subscript>System

Anodic oxidation of highly oriented pyrolytic graphite in an electrolyte containing concentrated sulfuric and anhydrous phosphoric acids is studied for the first time. The synthesis was carried out under galvanostatic conditions at a current I = 0.5 mA and an elevated temperature (t = 80°C). Intercalation compounds of graphite (ICG) are shown to form at all concentration ratios of H₂SO₄ and H³PO⁴ acids. The intercalation compound of step I forms in solutions containing more than 80 wt % H₂SO₄, a mixture of compounds of intercalation steps I and II forms in 60% H²SO⁴, intercalation step II is realized in the sulfuric acid concentration range from 10 to 40%, and a mixture of compounds of intercalation steps III and II is formed in 5% H₂SO₄ solutions. The threshold concentration of H₂SO₄ intercalation is ∼2%. With the decrease in active intercalate (H₂SO₄) concentration, the charging curves are gradually smoothed, the intercalation step number increases, and the potentials of ICG formation also increase. As the sulfuric acid concentration in the electrolyte changes from 96 to 40 wt %, the filled-layer thickness d _i in ICG monotonously increases from 0.803 to 0.820 nm, which apparently is associated with the greater size of phosphoric acid molecules. With further increase in H₃PO₄ concentration in solution, d _i remains unchanged. According to the results of chemical analysis, both acids are simultaneously incorporated into the graphite interplanar spacing and their ratio in ICG is determined by the electrolyte composition.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 651–655.Original Russian Text Copyright © 2005 by Leshin, Sorokina, Avdeev.     

Composés d’intercalation du graphite : des binaires aux ternaires

Graphite intercalation compounds: from binaries to ternaries. Graphite, which is an amphoteric host structure, easily reacts with electropositive elements and especially with alkali metals, leading to binary graphite–metal intercalation compounds. Alkali metals can also help elements unable to react alone with graphite to intercalate. Therefore, ternary intercalation compounds are obtained using various synthesis routes. To cite this article: C. Herold, P. Lagrange, C. R. Chimie 6 (2003).     

氧化环境和比例对改性Hummers法制备GO的影响

以鳞片石墨(GR)为原料,采用改性Hummers法液相氧化方法制备氧化石墨,通过超声剥离的方法剥离出片状的氧化石墨烯(GO),探讨了H₂SO₄环境与H₂SO₄+H₃PO₄混酸环境和KMnO₄与GR的比例对GO制备的影响。采用FTIR、UV、TG、XRD、SEM和XPS等分析手段对制备的GO进行分析。结果表明：GO外貌是呈褶皱片状,在片层上主要有C=O、C-OH、-COOH和C-O-C等官能团,以共价键形式存在石墨层间;通过TG与XPS数据分析表明在H₂SO₄ H₃PO₄混酸环境下制备的GO含氧官能团较多,并且(KMnO₄)与鳞片石墨的最佳比例是1:4。     

Intercalation von Lanthanoidtrichloriden in Graphit

Intercalation of Lanthanide Trichlorides in Graphite The reactions of the whole series of lanthanide trichlorides with graphite have been investigated. Intercalation compounds have been prepared with the chlorides of Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y whereas LaCl₃, CeCl₃, PrCl₃ and NdCl₃ do not intercalate. The compounds were characterized by chemical and X-ray analysis. The amount of c-axis increase in consistent with the assumption that the chlorides are intercalated in form of a chloride layer sandwich resembling the sheets in YCl₃. The chlorides which do not intercalate crystallize in the UCl₃ structure having 3 D arrangements of ions. Obviously, these chlorides cannot form sheets between the carbon layers. The ability of AlCl₃ to volatilize lanthanide chlorides through complex formation in the gas phase can be used to increase the intercalation rate strikingly.