Graphite Intercalation Compounds Research Articles

First-Principles Understanding of the Staging Properties of the Graphite Intercalation Compounds towards Dual-Ion Battery Applications.

Graphite-based dual-ion batteries are a promising alternative to the lithium-ion batteries for energy storage because of its potentially lower cost, higher voltage, and better safety. Among the most important materials in the dual-ion battery are the graphite and graphite intercalation compounds (GICs), whose properties determine the performance of electrodes. The GICs are formed at both anode and the cathode sides during the charging process in which the graphene sheets and the intercalants are arranged in an ordered way called the staging of GICs. Staging is one of the important structural features of GICs related to the volume expansion of the electrodes, the charging rate, and the capacity of the battery. However, the details of the staging mechanism, such as the structural properties, the electronic structure, and the voltage dependence on the stages are still poorly understood. In this regard, we perform density functional theory studies to explore these issues in GICs. Using staging models, we examine the stability of GICs at different stages of intercalation with a range of species (i.e., Li, Na, K, PF6, BF4, TFSI, AlCl4, and ClO4). We then study the contribution of intercalants to the electronic band structures in GICs. In addition, the voltage profiles of the dual-ion batteries with different intercalation species, intercalation stages, and battery capacities are also analyzed. The present work is important for the better understanding of graphite-based dual-ion batteries and helpful in development of novel energy storage systems.

Experimental and computational studies of electrochemical anion intercalation into graphite from target-oriented designed borate-based ionic liquid electrolytes

Here, we report on the fundamental experimental and computational analyses of target-oriented designed ionic liquid (IL) electrolytes composed of small and (electro)chemically stable borate-based anions with respect to their anion intercalation/de-intercalation behavior in graphite positive electrodes for dual-ion batteries (DIBs). Due to their relatively small size, borate-based anions (e.g., BF4ˉ) and electrolytes are of high interest for DIB cells in order to achieve a high specific capacity, which can, however, be impeded by electrolyte solvation effects. In order to exclude solvent effects, we develop and synthesize novel room-temperature IL electrolytes (RTILs), i.e., Pyr1101BF4/LiBF4 and Pyr1101CF3BF3/LiCF3BF3, which are characterized with respect to stability and anion intercalation behavior. These studies are combined with computational studies to gain fundamental insights into the electronic structures of the BF4ˉ and CF3BF3ˉ acceptor-type graphite intercalation compounds (GICs), staging stoichiometries, theoretical capacities and anion transport properties.

Superconductivity of alkali-metal intercalated BC2

The superconductivity of alkali-metal intercalated BC2, MxBC2 (M = Li, Na, and K; x = 0.5–1.5), has been studied using first-principles calculations. The calculated critical temperature (Tc) values are substantially high at x = 0.5 (49.8–57.1 K), which are higher than those for MgB2 and close to those predicted for LixByCz compounds. The Tc values at x = 1.5 are comparatively low (0.6–5.6 K) and close to those for graphite intercalation compounds. No superconductivity is observed at x = 1.0 for all alkali metals. An analysis of the electronic structures reveals that at x = 0.5, the state at the Fermi energy includes the σ bond character. In contrast, at x = 1.5, the state includes only π bonds comprising pz orbitals of B and C atoms. The σ bond character is essential for attaining high Tc values because the σ bond couples strongly with the bending-like phonon modes of the BC2 layer. However, the π bond couples weakly with the stretching-like phonon modes due to the small overlap of the pz orbitals, which results in a relatively low Tc for the material.

Intercalation of sodium and heavy alkali metals into graphenic foams

Abstract Most of alkali metals are well-known to easily intercalate into graphite to form stage-1 graphite intercalation compounds (GIC) whose structure and physical properties have been extensively studied. This work is focused on the intercalation of potassium, sodium and cesium into graphenic foams prepared by a solvothermal-based process. The as-obtained samples are analyzed by means of X-ray diffraction and Raman spectroscopy, and reveal a double phenomenon: the intercalation of alkali metals between the interplanar spaces of the multi-layer graphene stackings, and their sorption into the porosity of the host sample. This kind of behavior has already been reported when studying the reactivity of alkali metals with disordered carbon. Interestingly, our study shows a low stage intercalation in the case of sodium. Moreover, the dispersion of the potassium-intercalated samples into a polar solvent leads to a few-layer graphene dispersion stable for months.

Thermal exfoliation of electrochemically synthesized graphite intercalation compound with perrhenic acid

In present work, we describe the synthesis of graphite intercalation compounds with perrhenic acid (HReO4-GIC) through the anodic oxidation of graphite in aqueous perrhenic acid solution and their thermal exfoliation. Due to electrochemical treatment of graphite in perrhenic acid solution, ReO4− ions are intercalated into interlayer spaces of graphite. Anodic oxidation of graphite in HReO4 solution leads to the formation of 3-stage GIC. Simultaneously, some amount of perrhenic acid becomes deposited on the graphite surface and edges. In the next step, thermal treatment of the previously synthesized GIC was performed, causing both the exfoliation of graphitic structure and transformation of perrhenic acid into rhenium oxides on the surface of graphene layers. The yielded product was exfoliated graphite-ReO2/ReO3 composite. The obtained composite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy. Additionally, specific surface area of the exfoliated materials was measured.

Graphene-Silica Hybrids Fillers for Multifunctional Solution Styrene Butadiene Rubber

A nanohybrid filler of functionalized graphene created with eco-friendly coupling agents (ECAs) and silica was fabricated by decorating silica onto graphene through a sol-gel process. To do this, relatively large high-quality graphene flakes with an extremely low oxygen content were fabricated using a ternary graphite intercalation compound method. The ECAs with hydrophobic and the hydrophilic groups mitigate graphene aggregation while also acting as an interfacial or bridging material. Furthermore, graphene-silica nanohybrids (GSNs) were incorporated by compounding to solution-styrene-butadiene rubber (SSBR) through mechanical mixing. The GSN-embedded SSBR matrix shows remarkable enhancements in the mechanical properties, thermal and electrical conductivities, and the gas barrier properties, even at a low loading rate, due to the efficient dispersion of GSNs, which enhances the interaction with the rubber matrix. The incorporation of GSNs improved the storage modulus considerably upon evolution of the filler network and with the creation of a crosslinking network of the composites.

Pitch Derived Carbon As Light Weight and High-Power Sodium-Ion Battery Anode

Li-ion batteries (LIBs) are fulfilling the current need of humankind, the high abundance, and accessibility of sodium, making Na-ion batteries (NIBs) a promising LIBs supplement in the large-scale energy storage application.1, 2 However, the commercial success of NIBs demands an appropriate cathode and anode material. From the cathode material viewpoint, the literature reports suggest that O3/P2 type layered oxide can deliver a reasonable capacity with good cycling stability2. Graphite, the state-of-art anode material in LIBs is electrochemically inactive to intercalate Na-ions. Na-ion intercalation into graphite lattice is a thermodynamic driven process, where most Na-rich graphite intercalation compounds (GIC) prepared to date is NaC64 with a1 capacity of only 35 mAh g-1.3 However, Li-ion and K-ion form the stage one Li-GIC and K-GIC having the formula LiC6 and KC8, which makes them electronically active in Li- and K-ion battery, respectively. 4,5 To realize the large scale application of sodium-ion batteries, a stable, cost-effective anode is desired. Carbon-based anode materials are always attractive because of ease of fabrication, cost, and feasibility towards practical application. The pioneering work of Dahn and Stevens on hard carbon anode, reports the sodiation capacity of 300 mAh g-1 at room temperature.6 Later on, the hard carbon derived from different precursors such as a polymer, biomass, resin, etc., and applied as anode for Na-ion battery.7 However, hard carbon materials mostly suffer from poor carbon synthesis yield and high cost.8 Therefore, exploring cost-effective precursors and process is very crucial to realize the large scale application of NIB.Pitch is a potential low-cost precursor to synthesize soft carbon anode for NIBs. However, it does not exhibit decent Na-ion storage. Herein, we report the facile synthesis of pitch derived-binder less-metal free-freestanding anode for storing Na-ions by one-step pyrolysis process between the temperature range 700-1000 oC under nitrogen atmosphere. We replace conventional Cu-current collectors with carbon fiber (CFs). The electrode architecture not only eliminates the metallic current collector, conductive diluents and inactive organic binder but also provides an ideal porous network for sodium-ion and electrolyte diffusion into the bulk of the electrode. The freestanding electrode delivers a reversible capacity of 310 mAh g-1 in compare to 180 mAh g-1 for conventional electrode at the current density of 50 mA g-1. The cycling stability over 500 cycles (at 1 A g-1) and C-rate performance of freestanding anode dictate it as a promising anode for NIBs. The overall charge storage properties of conventional and freestanding-film are quantified into pseudocapacitive and diffusion-control Na+ intercalation. Further, the freestanding film is implemented as anode in order to realize its practical application in sodium-ion full cell. It is believed that the study may open up a new approach to modify the pitch based soft-carbon precursors as anode for low-cost, high-energy NIBs. Acknowledgments SG acknowledges MHRD, VKK acknowledges UGC-NET, Govt. of India, and SKM acknowledges Research Center Imarat (DRDO), Hyderabad under grant no. RCI/CAAT/8151/CARS-358 for financial support.

A method for quantitative analysis of gases evolving during formation applied on LiNi0.6Mn0.2Co0.2O2 ∣∣ natural graphite lithium ion battery cells using gas chromatography - barrier discharge ionization detector

To understand the overall processes behind the decomposition of state-of-the-art organic liquid electrolytes in lithium ion batteries (LIBs), it is necessary to investigate and quantify the permanent gases and light hydrocarbons evolving during electrolyte decomposition. In this work a convenient way of sampling gas from pouch cells without any previous preparation of the cell as well as a comprehensive gas chromatographic (GC) investigation of the gas phase is shown. A barrier discharge ionization detector (BID) was utilized for gas quantification and a multi component gas standard in combination with a gas mixing device was implemented to prepare calibration standards for validation. Therefore, sensitivity, linearity and reproducibility as well as the limits of detection (LOD) and limits of quantification (LOQ) were determined.Gas samples from pouch cells using LiNi0.6Mn0.2Co0.2O2 as cathode material and natural graphite (NMC622 ∣∣ NG) as anode material were analysed after formation. Gas volume and gas composition are key factors for a sufficient formation of LIBs and of interest for research with respect to the development of new materials and additives.

Thermal Decomposition of Ternary Sodium Graphite Intercalation Compounds.

Graphite intercalation compounds (GICs) are often used to produce exfoliated or functionalised graphene related materials (GRMs) in a specific solvent. This study explores the formation of the Na‐tetrahydrofuran (THF)‐GIC and a new ternary system based on dimethylacetamide (DMAc). Detailed comparisons of in situ temperature dependent XRD with TGA‐MS and Raman measurements reveal a series of dynamic transformations during heating. Surprisingly, the bulk of the intercalation compound is stable under ambient conditions, trapped between the graphene sheets. The heating process drives a reorganisation of the solvent and Na molecules, then an evaporation of the solvent; however, the solvent loss is arrested by restacking of the graphene layers, leading to trapped solvent bubbles. Eventually, the bubbles rupture, releasing the remaining solvent and creating expanded graphite. These trapped dopants may provide useful property enhancements, but also potentially confound measurements of grafting efficiency in liquid‐phase covalent functionalization experiments on 2D materials.

The Electromagnetic Absorption of a Na-Ethylenediamine Graphite Intercalation Compound.

A sodium-ethylenediamine graphite intercalation compound (Na(ethylenediamine)C15: "GIC") made from graphite flakes was used to study the microwave absorption performance of a GIC for the first time. Compared with the pristine graphite flakes, the neighboring layers in this GIC are pillared by Na(ethylenediamine)+ and possess a larger layer distance and improved electrical conductivity. Owing to the electrical conductivity of this GIC, only half of the loading content, compared to graphite flakes, is needed to achieve an outstanding absorption of -75.6 dB at 9.25 GHz (10.0 wt % GIC in paraffin in a 4.0 mm thick sample), but for graphite, 20.0 wt % is required for an absorption of -37.6 dB.

Performance Enhancement of PVDF/LiCIO4 Based Nanocomposite Solid Polymer Electrolytes via Incorporation of Li0.5La0.5TiO3 Nano Filler for All-Solid-State Batteries

Experimental and computational techniques have been applied to investigate the influence of Li0.5La0.5TiO3 nanoparticles on the ionic conductivity of the poly(vinylidene fluoride) (PVDF)/LiClO4 nanocomposite solid polymer electrolyte. The theoretical evidence facilitated to suggest a plausible mechanism for Li-ion conduction across the PVDF/LiClO4/Li0.5La0.5TiO3 based solid polymer electrolytes. The solid composite polymer electrolyte with 30wt% of Li0.5La0.5TiO3 (LLTO) nanofiller exhibited an unprecedented ionic conductivity of 2.3687 × 10−3 S cm−1 at room temperature. The addition of LLTO nanoparticles to the polymer matrix enhanced its ionic conductivity by two orders of magnitude. The activation energy (Ea) and total transference number (t) were estimated to be 0.29 eV and 0.853, respectively. The interaction between the filler and polymer matrix has been inferred by the density functional theory (DFT)-IR analysis. The DFT calculations have been performed on the above system using the basis set of B3LYP-LANL2DZ. The calculated IR spectra were compared with the experimental FTIR data, which allowed us to propose accurate vibrational assignments and to clarify the complex IR vibration of the samples. All-solid-state Li2FeSiO4/CPVDF/LiClO4/LLTO graphite lithium cell has been fabricated using the highest Li-ion conducting PVDF/LiClO4/LLTO composite polymer electrolyte. The all-solid-state cell exhibits an excellent initial specific capacity of 87.13 and 73.24 mAh g−1 after 30 cycles, demonstrating higher capacity retention. The findings provide an avenue for exploring the simple all-solid-state lithium batteries, which are potential candidates for next-generation energy storage technology.

Flowable sulfur template induced fully interconnected pore structures in graphene artefacts towards high volumetric potassium storage

Abstract Graphite intercalation compounds are promising anode materials for potassium-ion batteries, but still have problems of sluggish kinetics and a large volume expansion upon potassiation. Porous carbons with a large ion-accessible area used as anode materials can have a high gravimetric capacity and structural stability. However, to avoid a low volumetric performance in porous carbons, an electrode must have both a high density and fast ion-transport channels and these pose stringent requirements for the pore structure. Here we use a flowable sulfur template to produce continually- and precisely-tunable pores in three-dimensional graphene assemblies. During capillary drying of graphene hydrogel, sulfur accompanied with the shrinking graphene sheets controls the formation of pores with precise sizes by tuning the usage. The pores formed are open and interlinked due to the existence of a flowable sulfur template in the graphene network. This obtained graphene-assembly with well-controlled interconnected pores is used as potassium-ion battery anodes and gives a stable cycling performance (500 cycles) and an ultrahigh volumetric capacity.

Relaxation stage analysis of lithium inserted graphite

Relaxation analysis has been carried out on lithium graphite intercalation compound (Li-GIC) focusing on the variation of stage structure and graphene interlayer distances. X-ray diffraction coupled with the one-dimensional Rietveld analysis revealed that, after the termination of electrochemical lithium insertion, excessively formed stage I partly transforms into stage II during the relaxation process. In addition, the periodic stacking of defective lithium layers forming stage II orders the lithium occupation at the relaxation, which is more apparently observed for faster charged sample. Even after the lithium extraction, gradual stage changes from I to II accompanied by the ordering of lithium occupation in stage II have been observed at the relaxation process. Lithium ion is rather uniformly intercalated or deintercalated in the graphene interlayers, while Li-GIC turned into ordered stage structure to achieve the stable state at the relaxation time.

Direct Evidence of Charge Transfer upon Anion Intercalation in Graphite Cathodes through New Electronic States: An Experimental and Theoretical Study of Hexafluorophosphate

Graphite intercalation compounds continue to be central to technologies for electrochemical energy storage from anodes in established Li-ion batteries to cathodes in beyond Li-ion concepts paired w...

Room temperature synthesis of fluorinated graphite intercalation compounds with low fluorine loading of host matrix

The interaction of graphite with a gaseous mixture of BrF3 and Br2 at room temperature produced fluorinated graphite intercalation compounds with bromine. By changing the concentration of BrF3 in Br2 from 6.2 to 2.9 % we were able to obtain matrices of fluorinated graphene layers (C2Fx)n with x = 0.76, 0.66, 0.35, 0.25. It was shown that bromine was completely replaced by acetonitrile in the (C2Fx)n with x > 0.6, while two types of guests (CH3CN and Br2) were present between the layers with the lower fluorine loading. The Van der Waals forces hold CH3CN molecules in the (C2Fx)n host. The interaction of Br2 molecules with sp2-carbon regions remained in the C2Fx layers has donor-acceptor type. The models of guest molecules packing in host matrices (C2Fx)n are considered using the data on the stoichiometry and X-ray diffraction analysis.

PF6− Intercalation into Graphite Electrode from Gamma-butyrolactone/ethyl Methyl Carbonate

PF6− intercalated graphite compounds have found promising applications in dual-ion batteries. However, the anion storage mechanisms of graphite positive electrode in different organic solvents have not been well understood yet, especially in the mixed solvents. In this report, PF6− storage behavior in graphite electrode in 1 M LiPF6-GBL/EMC solutions is studied by conventional electrochemical tests like galvano-static charge-discharge and cyclic voltammetry at first. Then the combined electrochemical in situ characterizations including both in situ X-ray diffraction and electrochemical quartz crystal balance on graphite electrodes are carried out to trace their changes of crystal structure and mass during the anion storage. It is discovered that with EMC addition in the solutions, EMC rather than GBL will preferentially solvate with PF6− anion as the intercalant species. Moreover, ionic conductivity values and NMR spectra of the solutions were measured to investigate the interactions between ions and solvents inside, and are correlated with the performance of graphite electrode.

Development of Safe and Sustainable Dual‐Ion Batteries Through Hybrid Aqueous/Nonaqueous Electrolytes

AbstractIn this study, a new dual‐ion battery (DIB) concept based on an aqueous/non‐aqueous electrolyte is reported, combining high safety in the form of a nonflammable water‐in‐salt electrolyte, a high cathodic stability by forming a protective interphase on the negative electrode (non‐aqueous solvent), and improved sustainability by using a graphite‐based positive electrode material. Far beyond the anodic stability limit of water, the formation of a stage‐2 acceptor‐type graphite intercalation compound (GIC) of bis(trifluoromethanesulfonyl) imide (TFSI) anions from an aqueous‐based electrolyte is achieved for the first time, as confirmed by ex‐situ X‐ray diffraction. The choice of negative electrode material shows a huge impact on the performance of the DIB cell chemistry, i.e., discharge capacities up to 40 mAh g−1 are achieved even at a high specific current of 200 mA g−1. In particular, lithium titanium phosphate (LiTi2(PO4)3; LTP) and lithium titanium oxide (Li4Ti5O12; LTO) are evaluated as negative electrodes, exhibiting specific advantages for this DIB setup. In this work, a new DIB storage concept combining an environmentally friendly, transition‐metal‐free, abundant graphite positive electrode material, and a nonflammable water‐based electrolyte is established, thus paving the path toward a sustainable and safe alternative energy storage technology.

Studies on synthesis of graphite intercalation compounds in electrolytes containing sodium ion

Studies on synthesis of graphite intercalation compounds in electrolytes containing sodium ion

Challenges and prospects of polyatomic ions' intercalation in the graphite layer for energy storage applications.

Global population explosion has led to the rapid revolution of science and technology, and the high energy demand has necessitated new and efficient energy conversion and storage systems. Lithium ion batteries (LIBs) have a high potential window, high capacity, and high stability, but suffer from high cost and low safety. Therefore, many alternative batteries, including sodium ion batteries (NIBs), potassium (KIBs), aluminum (AIBs), and dual ion batteries (DIBs), have been introduced. One of the key working principles of these batteries is based on cation or anion intercalation in the graphite layers, and leads to the formation of graphite intercalation compounds (GICs). Recently, studies based on determining a reaction mechanism to improve the performance of the batteries have been conducted. In this review, an overview of the work on the reaction mechanism of polyatomic ions intercalated into GICs, the structure of intercalated polyatomic ions, the structure of the accommodated GICs, and their staging is provided. In other words, this review focuses on unraveling and understanding the reaction mechanisms for the intercalation of polyatomic ions into GICs by in situ and ex situ techniques, correlated with computational studies. The current limitations and future prospects of polyatomic ions intercalation batteries are also discussed.

Formation of a N2O5–graphite intercalation compound by ozone treatment of natural graphite

In this work, for the first time a stage-2 graphite intercalation compound with dinitrogen pentoxide (N2O5-GIC) by only ozonation of natural graphite is prepared.