Stage Intercalation Compounds Research Articles

Localized High‐Concentration Electrolytes Boost Potassium Storage in High‐Loading Graphite

AbstractReversible intercalation of potassium‐ion (K+) into graphite makes it a promising anode material for rechargeable potassium‐ion batteries (PIBs). However, the current graphite anodes in PIBs often suffer from poor cyclic stability with low coulombic efficiency. A stable solid electrolyte interphase (SEI) is necessary for stabilizing the large interlayer expansion during K+ insertion. Herein, a localized high‐concentration electrolyte (LHCE) is designed by adding a highly fluorinated ether into the concentrated potassium bis(fluorosulfonyl)imide/dimethoxyethane, which forms a durable SEI on the graphite surface and enables highly reversible K+ intercalation/deintercalation without solvent cointercalation. Furthermore, this LHCE shows a high ionic conductivity (13.6 mS cm−1) and excellent oxidation stability up to 5.3 V (vs K+/K), which enables compatibility with high‐voltage cathodes. The kinetics study reveals that K+ intercalation/deintercalation does not follow the same pathway. The potassiated graphite exhibits excellent depotassiation rate capability, while the formation of a low stage intercalation compound is the rate‐limiting step during potassiation.

Potassium-Ion Intercalation into Graphite for High-Voltage and High-Power Batteries

Rechargeable lithium batteries have been recognized as the most successful and sophisticated energy storage devices since their first commercialization in 1991 by Sony. Furthermore, they are used now as an alternative power source for electric motors instead of combustion engines equipped with a fuel tank.1 Electric vehicles equipped with large-scale lithium batteries as power sources have been introduced to the automotive market, promising to reduce the dependence of transportation on fossil fuels in the future. The element lithium is widely distributed in the Earth’s crust and sea, but is not regarded as an abundant element. In contrast, potassium is the seventh most-abundant element in the continental crust and a major element in oceanic waters.2 Furthermore, the standard potential of potassium is lower than that of lithium in propylene carbonate.3 In this study, the electrochemical potassium intercalation into graphite negative electrode is investigated to realize rechargeable potassium-ion batteries. The working electrodes consisted of 90 wt% graphite and 10 wt% binder: poly(vinilydene fluoride) (PVdF), carboxymethyl cellulose (CMC), or sodium polyacrylate (PANa). Metallic potassium foil was used as a counter electrode. The galvanostatic charge/discharge measurements were carried out at C/10 (25 mA g-1) in the voltage range of 0-2 V vs. K/K+. In situ X-ray diffraction (XRD) was conducted for electrodes in K cell. The surface of the electrodes after cycles was characterized by hard X-ray photoelectron spectroscopy (HAXPES), soft X-ray photoelectron spectroscopy (SOXPES), time-of-flight secondary ion mass spectrometry (TOF-SIMS) and scanning electron microscopy (SEM). In Fig. 1a, graphite electrode with PANa binder shows better cyclability than those of electrodes with PVDF and CMC binder due to the interfacial modification, with delivering ca. 250 mAh g-1 of reversible capacity and excellent capacity retention in 1 mol l-1 KFSI EC:DEC solution. In addition, graphite electrode with PANa demonstrates ultrahigh oxidation rate capability of depotassiation up to 40C (11160 mA g-1) rate in a non-aqueous potassium cell as shown Fig. 1b. Furthermore, in-situ XRD confirms reversible phase transition from graphite to different stage intercalation compounds, such as KC8 and KC24. In addition, HAXPES results demonstrate that surface of a graphite electrode is covered with a passive layer after 1st cycle, and no obvious difference between 1st and 10thcycle is observed in the surface layer. From these results, we will further discuss graphite negative electrode for potassium-ion batteries as next-generation battery beyond lithium-ion and sodium-ion.

Heteroatom-substituted carbon alloys for use in energy conversion and storage systems

Carbon-based materials containing heteroatoms, such as boron and nitrogen, are called heteroatom-substituted carbon alloys. Preparation and applications of heteroatom-substituted carbon alloys, particularly materials composed of boron, carbon and nitrogen (B/C/N materials), and carbon and nitrogen (C/N materials) are summarized in this review. Examples of potential applications of the materials to energy conversion and storage systems, such as secondary batteries, capacitors and photocatalysts are described. B/C/N materials can be intercalated with sodium (Na) to form a first stage intercalation compound, which can be used as the anode of Na ion batteries. C/N materials used as the electrode of capacitors have higher volumetric capacities than commercially-used activated carbon, and show photocatalytic behavior as an electrode for the production of hydrogen by the electrolysis of water. Important roles of boron and nitrogen in B/C/N and C/N materials are also discussed. TANSO 2015 (No. 267), 84–93.

Van der Waals density functional study of the energetics of alkali metal intercalation in graphite

We report on the energetics of intercalation of lithium, sodium and potassium in graphite by density functional theory using recently developed van der Waals (vdW) density functionals. First stage intercalation compounds are well described by conventional functionals like GGA, but van der Waals functionals are crucial for higher stage intercalation compounds and graphite, where van der Waals interactions are important. The vdW-optPBE functional gave the best agreement with reported structure and energetics for graphite and LiC6 and was further applied for intercalation of Na and K. The enthalpy of formation of LiC6 and KC8 were found to be −16.4 and −27.5 kJ mol−1 respectively. NaC6 and NaC8 were unstable with positive enthalpies of formation (+20.8 and +19.9 kJ mol−1). The energetics of stacking of graphene and intercalant layers was investigated from first to fifth stage intercalation compounds. Higher stage compounds of Li and K were stable, but with less negative enthalpy of formation with increasing stage order. The higher stage Na compounds possessed positive enthalpy of formation, but lower in magnitude than the energy difference of 0.6 kJ mol−1 between graphite with AB and AA stacking. The abnormal behaviour of the lower stage Na intercalation compounds was rationalized by the lower energy involved in the formation of the chemical bond between carbon Na relative to the corresponding bond with Li or K. The chemical bond between alkali metal and carbon is characterized by charge transfer from the alkali-metal to carbon resulting in ionized alkali-metals. The intercalation induces only a subtle increase in the in-plane C–C bond lengths, with longer C–C bonds in the vicinity of the alkali metals but without breaking the hexagonal symmetry.

Intercalation chemistry of graphite-like layered material BC6N for anode of Li ion battery

Abstract Films with an approximate composition of BC6N were prepared by the reaction of acrylonitrile with boron trichloride (mole ratio=2:1) at 1470–2070 K under atmospheric pressure. The films obtained at 1470 and 2070 K had graphite-like layered structure whose interlayer spaces were 0.339 and 0.342 nm, respectively. Rapid chemical intercalation of Li into the BC6N prepared at 2070 K was observed in Li + C 10 H 8 − / 2 –MeTHF solution, resulting in formation of the first stage intercalation compound with an interlayer space (d-spacing) of 0.365 nm. The BC6N prepared at 1470 K performed electrochemical charge/discharge cycles similar to those of graphite in 1 M-LiPF6/EC+DEC solution. The first stage compound of LiXBC6N, which was prepared by the electrochemical method, had a d-spacing of 0.355 nm smaller than that of LiC6 (0.370 nm). The small expansion ratio in d-spacing [4.7%={(0.355–0.339)/0.339}×100] could be one of the advantages of the BC6N material for the usage as Li ion battery anode.

Selective anion-exchange intercalation of isomeric benzoate anions into the layered double hydroxide [LiAl2(OH)6]Cl·H2O

All the geometric isomers of the benzoate derivatives, XC6H4CO2− (X=F, Cl, Br, OH, OCH3, NO2, CO2CH3, NH2, N(CH3)2) can be intercalated into the layered double hydroxide [LiAl2(OH)6]Cl·H2O in 50% (v/v) water/ethanol solution at 80°C to give fully anion-exchanged first stage intercalation compounds [LiAl2(OH)6]G·yH2O (G=a substituted benzoate). The observed interlayer separations of the intercalates vary from 14.3Å for [LiAl2(OH)6](4-nitrobenzoate)·2H2O to 20.6Å for [LiAl2(OH)6](3-dimethylaminobenzoate)·3H2O. Competitive intercalation studies using mixtures of isomeric benzoates showed that the 4-isomers and 2-isomers are the most and the least preferred anions, respectively. Comparing the calculated dipole moments of the anions with the observed isomeric intercalation preferences suggests that dipole moment may be a good general index for the preference; however, it should be remembered that the bulkiness and electronegativity of the other substituent could be very important factors that affect the preferential intercalation.

The first in situ Li7 nuclear magnetic resonance study of lithium insertion in hard-carbon anode materials for Li-ion batteries

We show the first continuous in situ static Li7 nuclear magnetic resonance (NMR) experiment on a plastic lithium/carbon cell. The electrochemical cycling was successfully performed inside the magnet. We particularly studied the insertion/extraction of lithium in a material designed to be used as negative electrode in a secondary battery; hard carbon fibers treated to reduce the irreversible capacity (x=0.5). The reversible capacity is x=1.5 (in LixC6), higher than with graphite for which the saturating composition corresponds to the first stage intercalation compound LiC6 (x=1). Ex situ quantitative transmission electron microscopy gives a statistical description of the fibers; a core made of disorganized carbon coated by better organized pyrocarbon. Crossed with the values of capacity given by the current generator, in situ NMR indicates the chronology of the insertion. From the observed data, we propose that a Li–C metallic alloy is formed. By comparing the Knight shift with that of metal (Li0), we estimate the charge transfer from Li to C. Amongst the two types of lithium found, the first might be assigned to Li intercalating (Li+0.66) into the smallest spaces between the graphene layers. The second represents most of the reversible lithium and is assigned to be quasimetallic (Li+0.1). Its longitudinal relaxation time T1 is also near-metallic. The quality of this carbon comes from its ability to host such a species.

Preferential anion exchange intercalation of pyridinecarboxylate and toluate isomers in the layered double hydroxide [LiAl2(OH)6]Cl·H2O

All isomers of both pyridinecarboxylate (2-PA; 3-PA and 4-PA) and toluate (o-TA; m-TA and p-TA) can be intercalated into the layered double hydroxide [LiAl2(OH)6]Cl·H2O in water or a water–ethanol mixture at RT to give the fully ion-exchanged first stage intercalation compounds [LiAl2(OH)6]·G·yH2O (G = 2-PA; 3-PA; 4-PA; o-TA; m-TA and p-TA; y = 2.5–3.5). Experiments also showed that using a mixed ethanol–water solvent may improve the crystallinity and decrease the production of Al(OH)3. The observed interlayer separations for the intercalates vary from 14.9 A for [LiAl2(OH)6](4-PA)·3H2O to 16.7 A for [LiAl2(OH)6](p-TA)·2.5H2O. When [LiAl2(OH)6]Cl·H2O is added to a solution containing an equal concentration of two or three isomers of either pyridinecarboxylate or toluate anions, the host exhibits preferential anion-exchange intercalation. Following a series of competitive intercalation reactions involving two or three component mixtures we were able to determine the preference order for intercalation of both PA and TA guests in [LiAl2(OH)6]Cl·H2O. The order was found to be 4-PA > 2-PA > 3-PA and p-TA > m-TA > o-TA in water at both 20 and 80 °C.

Study of the reactivity of chalcogen hexafluorides with graphite

The intercalation reaction of chalcogen hexafluorides, EF 6 (E=S, Se, Te), with graphite was investigated. It occured only under a fluorine atmosphere and first stage intercalation compounds were obtained with TeF 6 or SeF 6, as well as a partial graphite fluorination. SF 6 did not intercalate but catalyzed the complete fluorination of graphite. All compounds were characterized by X-ray diffraction, thermogravimetric analysis, infrared and 19 F NMR spectroscopies. Entities, such as TeF 6 and SeF 6 were identified. Others, such as EF 7 −, EF 8 2−, …, and possible SeF n polymeric forms could exist. In all cases, the presence of fluorinated graphite was found.

Efficient separation of pyridinedicarboxylates by preferential anion exchange intercalation in [LiAl2(OH)6]Cl·H2O

All six isomers of pyridinedicarboxylate (2,3-PDA; 2,4-PDA; 2,5-PDA; 2,6-PDA; 3,4-PDA; 3,5-PDA) can be intercalated by the layered double hydroxide [LiAl2(OH)6]Cl·H2O in water at 100 °C to give the fully ion-exchanged first stage intercalation compounds [LiAl2(OH)6]G0.5·xH2O (G = 2,3-PDA; 2,4-PDA; 2,5-PDA; 2,6-PDA; 3,4-PDA; 3,5-PDA; x = 2–3.5) . The observed interlayer separations for the intercalates vary from 10.9 A for the high temperature form of [LiAl2(OH)6](3,5-PDA)0.5·2H2O to 14.8 A for [LiAl2(OH)6](2,3-PDA)0.5·3H2O. When a solution containing an equal concentration of two or more of the pyridinedicarboxylate anions is added to a suspension of [LiAl2(OH)6]Cl·H2O in water then the host exhibits preferential anion-exchange intercalation. Following an extensive series of competitive intercalation reactions involving two component through to six component mixtures we were able to determine the preference order for intercalation of all six PDA guests in [LiAl2(OH)6]Cl·H2O. The order was found to be 2,5-PDA > 2,3-PDA > 2,4-PDA > 2,6-PDA ≈ 3,5-PDA ≈ 3,4-PDA in water at 100 °C.

The generation of nanometer-size tantalum particles in a graphite host lattice

Tantalum(V) chloride was intercalated from the gas phase into highly oriented pyrolytic graphite and into natural graphite. Second stage intercalation compounds were produced. The TaCl5–graphite intercalation compounds were heated in a hydrogen atmosphere for 1week at 200°C. The flakes showed no exfoliation, but reduction was insufficient at this temperature. A reduction for 1week at 1000°C produced extensively exfoliated samples. After 1week at 1000°C in a hydrogen atmosphere, it was still possible to detect chlorine in some regions by energy-dispersive X-ray analysis. However, transmission electron microscope images showed the occurrence of nanometer-size particles within the graphite host lattice, located near the prismatic edges and also at the center of the particles. Different morphologies of the particles were observed, namely two-dimensional platelets and numerous one-dimensional `chains', with particle sizes between 10 and 300nm. Selected-area electron diffraction patterns of the particles gave evidence as to their chemical nature. Metallic tantalum was formed by the reaction, the patterns gave also evidence that a small amount of TaCl5 had still survived.

Intercalation of Heavy Alkali Metals in Boron Substituted Carbons BxC1−x

First stage intercalation compounds were obtained using vapor reaction of heavy alkali metals (M ˭ K, Rb and Cs) with BXC1−x platelets (x=0.1 and x=0.25). Depending on the value of x, M(B0.1C0.9)8±1 and M(B0.25C0.75)10±1 compounds were formed. Intensity calculations of the 001 lines suggested domains of M(BXC1−x)5 first stage dense structure. As formed B0.25C0.75 was incompletely intercalated by cesium from its liquid ammonia solution whereas extended intercalation was obtained with heat treated B0.25C0.75 host (T=1600°C) giving a first stage Cs(B0.25C0.75)12 derivative.

Process of Intercalation of Manganese Chloride into Graphite Fibers and their Application in a Chemical Heat Pump

First stage intercalation compounds of manganese chloride were obtained in graphite fibers owing to chemical vapor transport with gaseous heterocomplexes. These intercalated fibers used in a chemical heat pump for the reaction with ammonia gave better performance in energy and power.

Potassium-oxygen graphite intercalation compounds

Intercalation of potassium superoxide KO 2 into graphite in the presence of potassium metal was studied. Graphite intercalation compounds of stage 1 (assigned formula C 4KO 2, c-axis repeat distance 8.44 Å) and stage 2 (assigned formula C 8KO 2, c-axis repeat distance 11.75 Å) were synthesized and isolated for the first time. A quadruple intercalate layer KOOK is supposed. In-plane structure of the intercalate layer is discussed mostly on the basis of X-ray diffraction intensity analysis and transmission electron microscopy electron diffraction. A metal-like temperature dependence of c-axis resistivity was obtained in the 1.5–300 K temperature range where the resistivity values at room temperature are 0.07 and 0.81 Ω cm for stage-1 and stage-2 compounds, respectively. The results of magnetic susceptibility measurements suggest that the oxygen species are in nonmagnetic states.

Atomic Resolution Surface Imaging of Binary and Ternary Stage 1 Alkali Metal Graphite Intercalation Compounds by Scanning Tunneling Microscopy

Abstract Li, K, Rb, Cs, KCs and RbCs graphite intercalation compounds of stage 1 are investigated by scanning tunneling microscopy in an inert-gas environment at 295 K. Various superlattice structures are identified such as 2 × 2, √3 × √3, √3 × 3, √3 × 4, √3 × √21, √3 × √27, √3 × √28 as well as incommensurate structures. Observed transformations between different superlattices are attributed to gradual loss of the intercalant.

Electrochemical Intercalation of Alkali Metal Ions into Graphite

The cyclic voltammograms of the graphite in LiClO4-DMSO, NaClO4-DMSO, KClO4-DMSO and RbClO4-DMSO solutions showed the cathodic current and the anodic current peaks corresponding to the intercalation and deintercalation processes of alkali metal ions, respectively. The x-ray diffraction patterns indicated the formation of the second stage intercalation compounds due to the cathodic reduction (electrode potential: 2.5V vs. SCE, electric quantity: 40 C) of graphite in each solution. The change of the electrode potential with time after cathodic reduction showed less self-discharge of K+-compound than other compounds.

Anodische Oberflächen- und Volumenoxidation graphitischer Materialien in neutralen und alkalischen wäßrigen Lösungen / Anodic Surface and Bulk Oxidation of Graphitic Materials in Neutral and Basic Aqueous Solutions

Anodic oxidation of graphitic materials in aqueous electrolytes is a complex process which may yield e.g. higher stage intercalation compounds and lamellar graphite oxides, acidic surface or defect oxides and gaseous or colloidal decomposition products. Kind and concentration of the electrolyte solution are the most important parameters to control this wide-spread distribution of products. Based on electrochemical and microscopic studies on HOPG and carbon fibres, a mechanistic concept of electrolyte effects is proposed: In dilute aqueous solutions, attack of OH• radicals formed in the primary electrochemical step is the dominant reaction pathway leading to formation of covalent carbon-oxygen bonds. Due to their reactivity, OH• radicals are able to attack basal plane carbon sites and also to create 3-dimensional defect oxides. Dissociation or capture of OH• radicals - which is favoured in basic and in most concentrated neutral solutions, respectively, - results in less active radical species and limits the attack to thermodynamically less stable carbon atoms at edge sites which may be either oxidized or removed. Due to acidification of the diffusion layer of anodes even in neutral aqueous electrolytes, direct current oxidation always yields higher stage acid intercalation compounds and lamellar graphite oxide as by-products. This can be almost prevented by alternating current oxidation.

Thermogravimetric study of gold(III) bromide graphite

Solutions of AuBr 3 in bromine react with graphite at 75°C to give graphite intercalation compounds of first stage. The intercalate consists of mixtures of Au 2Br 6 molecules and bromine. The GIC richest in AuBr 3 had the composition C 40AuBr 3·Br 5.2 with an interplanar distance d i = 707 pm. Upon heating stage 1 samples lose bromine and are transformed at 110°C to stage 2 gold(III) bromide GIC with d i = 1036 pm. The thermal decomposition of the compounds was studied by means of a magnetic suspension balance. Treatment of NiCl 2-graphite (st. 2, d i = 1264 pm) with AuBr 3 in bromine resulted in the formation of a bi-intercalation compound with the layer sequence GNiCl 2AuBr xG… (G graphene sheet) and the composition C 80AuBr 7.5 (NiCl 2) 7.75. d i was determined to be 1634 pm.

Preparation of Graphite Intercalation Compound of Niobium Fluoride in Fluorine Atmosphere

Abstract The 1st stage intercalation compound of graphite with niobium fluoride has been prepared in fluorine gas of 101 kPa. The composition is C8−10NbF6−7 with repeat distance of 0.818–0.834 nm. The highest electrical conductivity is 1.2×105 S cm−1 at stage 2+3.

Die thermische deintercalation von graphitintercalationsverbindungen der arsen- und antimonchloridfluoride

In the reaction of AsCl 2F 3 with graphite, intercalation compounds of stage n = 3 are produced with an identity period of I c = 1.49 nm. The stoichiometry of the compounds varies in consequence of the dissociation and dismutation reactions of AsCl 2F 3. The exfoliation of the crystals and the release of chlorine have been observed during heat treatment. The maximum thermal deintercalation is between 350 and 440°C. Only chlorine and arsenic trihalides, no pentahalides, have been detected by mass spectrometric analysis of the pyrolysis gases. Thermogravimetric investigations of SbCl mF 5-m graphite intercalation compounds as well as mass spectrometric analyses of the pyrolysis gases show that in the deintercalation of the original intercalated pentahalides, their thermal dissociation as well as dismutation by halogen exchange overlap in the course of thermal decomposition. The conversion of stage 1 SbCl 4F graphite to stage 2 and the formation of dilute stage 2 SbCl 5 graphite as well as SbCl 4F graphite take place at 80–110°C. A high concentration of the pentahalides SbCl 5 and SbCl 4F respectively and a low concentration of trihalides have been found by mass spectrometry in the gas phase at 80–110°C. This low-temperature deintercalation is assumed to be a complete or partial emptying of galleries without a structural modification of the graphite layers. The structural conversions of stages n > 2 into stages n + 1 at higher temperatures of about 200 and 300°C are explained by a Daumas-Hérold domain model. Powdered natural graphite and synthetic graphite exhibit a preferred deintercalation of halides at 80–110°C. This may be explained by a higher density of diffusion paths and a lower ratio of crystallite sizes to domain sizes with respect to graphite flakes. The thermal dissociation of the pentahalides beginning at 190–200°C overlaps with the conversion of stage 2 to stage 3. At the same time chlorine is explosively released, leading to the exfoliation of the graphite flakes. The conversions of higher stages open intercalate islands in the crystal bulk and, consequently, the concentrations of the pentahalides and their dissociation products in the gas phase increase. The conversion of stage 3 to stage 4 occurs in the temperature range of 300–350°C; stages n > 4 degrade between 400 and 430°C. SbCl 2F 3 graphite as well as AsCl 2F 3 graphite evolves only the dissociation and dismutation products of the pentahalides. With an increase of temperature, the relative concentrations of SbF 3 and AsF 3 increase with respect to those of the Cl-containing trihalides; this is a consequence of dismutation with halogen exchange. The formation of polymeric neutral or anionic Sb halide species with fluorine bridges is presumably the reason for the dismutation reactions.