Intercalation Compounds Research Articles

Charge–Discharge Behavior of Graphite Negative Electrodes in FSA-Based Ionic Liquid Electrolytes: Comparative Study of Li-, Na-, K-Ion Systems

K-ion batteries utilizing ionic liquid (IL) electrolytes are promising candidates for next-generation batteries because of the abundance of potassium resources, low redox potential of potassium, and high safety of ILs. Our major interest is in the comprehensive understanding of electrochemical alkali metal intercalation/deintercalation into graphite negative electrodes, because graphite can easily form graphite intercalation compounds (GICs) with various ionic species, but not with sodium. In this study, we investigated the potassium storage mechanism of graphite negative electrodes in bis(fluorosulfonyl)amide (FSA)-based ILs, and compared the electrochemical GIC formation of Li-, Na-, and K-ion systems. Charge–discharge tests of graphite in K[FSA]–[C3C1pyrr][FSA] IL (C3C1pyrr = N-methyl-N-propylpyrrolidinium) at 313 K yielded an initial discharge capacity as high as 268 mAh (g-C)−1, leading to the formation of several K-GICs including stage-3 KC36, stage-2 KC24, and stage-1 KC8. The rate capability and long-term cycling tests indicated stable potassiation/depotassiation behavior for 225 cycles. A comparison of the electrochemical behavior of graphite among M[FSA]–[C3C1pyrr][FSA] (M = Li, Na, and K) ILs at 298 K indicated that the formation of binary M-GICs is localized in the potential range below −2.85 V vs. Fc+/Fc (Fc = ferrocene), which possibly hinders Na-GIC formation.

Superconductivity in the α-Form Layer Structured Metal Nitride Halide

Layered metal nitride halides MNX (M = Ti, Zr, Hf; X = Cl, Br, I) have two polymorphs, including α- and β-forms, which have the FeOCl and SmSI structures, respectively. These compounds are band insulators and become metals and show superconductivity after electron doping by intercalating alkali metals between the layers. The superconductivity of β-form had been extensively characterized from decades ago, but it is not easy to consistently interpret all experimental results using conventional phonon-mediated Bardeen–Cooper–Schriefer mechanisms. The titanium compound TiNCl crystallizes only in the α-form structure. TiNCl also exhibits superconductivity as high as ~16 K after electron doping by intercalating metals and/or organic basis. It is important to compare the superconductivity of different M–N networks. However, α-form compounds are vulnerable to moisture, unlike β-form ones. The intercalation compounds are even more sensitive to humid air. Thus, there are few experimental studies on the superconducting mechanism of α-form, although it has been discussed for exotic Cooper-pairing mechanisms. This short review gathers the recent progress in experimental studies of TiNCl.

First Principles Study of Layered CrGeTe3 as Lithium Intercalation Compound

There have been unprecedented research efforts to produce efficient and sustainable electrode materials for lithium-ion batteries (LIB). The research efforts to increase energy density, life cycle, safety, and rate-capability are still in progress. This work is carried out to explore the prospects of a new anode material CrGeTe3 for use in LIB studied via first-principles predictions. The investigation of Li: CrGeTe3 system and lithiation mechanism in the proposed material pointed out its suitability for lithium intercalation compound. The energy-profiling at highly symmetry points in the host structure revealed that BGe-Cr is most favorable energy site for lithiation in the material. The maximum value of the lithium insertion voltage is 3.41 V and the storage capacity is 620.60 mAh g−1. The diffusion barrier faced by lithium atom is 0.27 eV which is the minimum value, while moving along the x-axis within the top and middle hexagonal rings. The steric interaction of Li with Ge and Te atoms pointed structural reliability and hence stable operation of the anode to address capacity fading problems in LIB.

K-Functionalized Carbon Quantum Dots-Induced Interface Assembly of Carbon Nanocages for Ultrastable Potassium Storage Performance.

Carbon nanocages (CNCs), with unique merits of morphology and structure, have attracted increasing attention for energy storage and conversion. However, the synthesis of CNCs reported so far suffers from relatively harsh conditions and expensive raw materials. Herein, porous CNCs are intelligently designed using low-cost glucose as the carbon precursor via a facile K-functionalized carbon quantum dots (K-CQDs)-induced assembly route under hydrothermal process. The resulting CNCs have a unique cage-like structure, large surface area, and rich carboxyl groups. With these elegant structural merits, the as-made CNCs anode shows a high reversible capacity of 270 mAh g-1 at 100mA g-1 after 200 cycles and a long-term cycling stability of 206 mAh g-1 at 2000mA g-1 after 4000 cycles. An intercalation reaction mechanism with the K+ intercalation compound is further identified through an in-situ Raman technique. Density functional theory simulations reveal that abundant carboxyl groups inherited from K-CQDs can significantly promote the potassium storage capacities of the CNCs electrode.

Free Energy Model for Lithium Intercalation in Graphite: Focusing on the Coupling with Graphene Stacking Sequence

During intercalation, some layered intercalation compounds undergo phase separation between several stable phases, known as stages. Of particular interest is the case of graphite, widely used in negative electrodes of batteries. Here, thermodynamics and kinetics of stage formation are studied using a multilayer free energy framework based on mean-field theory, accounting for both intralayer and interlayer interactions. More specifically, an order parameter is introduced to describe the local evolution of the stacking sequence of graphene sheets around lithium islands, enabling the distinction between the liquid-like stage 2L and the stage 2. In particular, we show that an interlayer interaction between the lithium ions and the host structure is necessary to counterbalance the enthalpic term of the lithium intralayer energy and allow the formation of islands with intermediate concentrations, characteristics of the liquid-like phases. Introducing the developed free energy model in Cahn–Hilliard’s and Allen–Cahn’s equations, we study the stages emergence during spinodal decompositions. Staggered domains of lithium surrounded by different graphene stacking arise naturally with characteristics typical of stages 1′, 3L, 2L, 2, and 1.

Synthesis and Characterization of Graphite Intercalation Compounds with Sulfuric Acid

In this work, graphite intercalation compounds (GICs) were synthesized using three different oxidizers: (NH4)2S2O8, K2S2O8, and CrO3 with and without P2O5 as a water-binding agent. Furthermore, the samples obtained were heat-treated at 800 °C. Specimens were characterized by optical microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), and scanning electron microscopy (SEM). The correlation between different characteristic parameters of the Raman analysis has shown that the use of CrO3 results in a much higher structural disorder compared to the products obtained using persulfate oxidizers. Narrowing the correlation set revealed that minimal defect concentration can be reached by using K2S2O8, while the use of (NH4)2S2O8 causes a slightly higher concentration of defects. It was also established that the additional use of P2O5 can help to achieve more effective intercalation and has a positive effect on the formation of the stage I GIC phase. After heat treatment, the intercalated products mostly return to a graphite-like structure; however, the samples obtained with CrO3 stand out with the most significant changes in their surface morphology. Therefore, analysis suggests that GICs obtained using persulfate oxidizers and P2O5 could be a candidate to produce high-quality graphene or graphene oxide.

Green and simple production of graphite intercalation compound used sodium bicarbonate as intercalation agent

In view of the technical difficulties in the preparation of graphite intercalation compound (GIC) such as complex processes, the need to use strong acid reagents, and the product containing corrosive elements. A novel, efficient and simple method used sodium bicarbonate as intercalation agent was developed, which combined with mechanical force and chemical method for the green production of GIC. The production parameters were optimized by the single factor experiments, the optimal conditions were the ball mill speed 500 r/min for 4 h (6 mm diameter of the stainless-steel beads as ball milling media), the decomposition temperature 200 ℃ for 4 h, and 1:1 mass ratio of flake graphite to sodium bicarbonate. SEM results revealed that the prepared product appears the lamellar separation, pores, and semi-open morphology characteristic of GIC. FT-IR results indicated that the preparation method does not change the carbon-based structure, and the sodium bicarbonate intercalant has entered the interlayer of graphite flakes to form GIC. XRD results further showed that the GIC products still maintained the structure of carbon atoms or molecules, and the sodium bicarbonate intercalation agent has entered the interlayer of the graphite, and increased the interlayer distance of the layered graphite. The expandability of GIC products was studied, and the results show that it was expandable, and the expandable volume of GIC products prepared under optimal conditions has reached 142 mL/g. The theoretical basis for large-scale production was provided by studied the mechanism of the preparation method and designed the flow chart. The method has the advantages of simple process, products free of impurities, no use of aggressive reagents, process stable, and does not pollute the environment, being favorable to mass production, and provided new preparation method and idea for two-dimensional nanomaterials with preparation technical difficulties.

LiCl2]− Superhalide: A New Charge Carrier for Graphite Cathode of Dual‐Ion Batteries

AbstractNew acceptor‐type graphite intercalation compounds (GICs) offer candidates of cathode materials for dual‐ion batteries (DIBs), where superhalides represent the emerging anion charge carriers for such batteries. Here, the reversible insertion of [LiCl2]− into graphite from an aqueous deep eutectic solvent electrolyte of 20 m LiCl + 20 m choline chloride is reported. [LiCl2]− is the primary anion species in this electrolyte as revealed by the femtosecond stimulated Raman spectroscopy results, particularly through the rarely observed H–O–H bending mode. The insertion of Li–Cl anionic species is suggested by 7Li magic angle spinning nuclear magnetic resonance results that describe a unique chemical environment of Li+ ions with electron donors around. 2H nuclear magnetic resonance results suggest that water molecules are co‐inserted into graphite. Density functional theory calculations reveal that the anionic insertion of hydrated [LiCl2]− takes place at a lower potential, being more favorable. X‐ray diffraction and the Raman results show that the insertion of [LiCl2]− creates turbostratic structure in graphite instead of forming long‐range ordered GICs. The storage of [LiCl2]− in graphite as a cathode for DIBs offers a capacity of 114 mAh g−1 that is stable over 440 cycles.

Synthesis, crystal structure and electronic structure of AgxZrTe2

A systematic study of the crystal and electronic structure of the intercalation compound AgxZrTe2 in the Ag concentration range of x = 0–0.37 has been performed. It was found that the Ag atoms occupy the sites in the interlayer gap that are tetrahedrally coordinated by the Te atoms. The chemical bond is provided by the Ag 4d/Te 5p hybridization. The comparison of the studied electronic structure with the available data on the electrochemical measurements of AgxZrTe2 in the temperature range of 200–400 °C indicates the formation of covalent centers accompanied by the formation of the half-filled band of Ag 4d/Te 5p hybridized states. The shape of the phase diagram in the region of low Ag concentrations coincides with that observed for AgxTiTe2, in which the stability of the covalent centers is confirmed by the Ag 5s/Ti 3d hybridization. This indicates the universal character of the influence of the localized or extended states of conduction electrons on the phase diagram of intercalation compounds.

First principles study of layered silicon carbide as anode in lithium ion battery

AbstractIn order to advance the current technology to cope with the future challenges, the search of anode materials beyond‐graphite for use in lithium ion battery is in progress. First principles calculations were conducted to investigate the prospects of SiC layers as lithium intercalation compound. In order to investigate electrolyte decomposition triggered by high lithium reactivity in Li:SiC anode the molecular dynamics computations were performed. The simulations to model the electrode‐electrolyte interface and temperature profiling were studied via reactive force field calculations that ruled out the reactivity at room temperature whereas uniform temperature afterwards sheds light on performance of the system. The diffusion coefficient of Li in layered SiC is calculated at different values of temperature. The ionic diffusion shown an activation energy of 0.046 eV whereas diffusion coefficient is found of the order 10−11 m2/s. The intercalation voltage calculated with grand canonical Monte Carlo simulation is found as 1.85 V. The ReaxFF simulations predicted that volume expansion in SiC layers appeared less than Si which shows the improved performance of the anode material.

Cation Diffusion Facilitated by Antiphase Boundaries in Layered Intercalation Compounds

Cation Diffusion Facilitated by Antiphase Boundaries in Layered Intercalation Compounds

Construction of novel electrochemical capacitors from lithium primary batteries using covalent-type graphite intercalation compounds

Construction of novel electrochemical capacitors from lithium primary batteries using covalent-type graphite intercalation compounds

Manipulating the Electronic Structure of Graphite Intercalation Compounds for Boosting the Bifunctional Oxygen Catalytic Performance.

Developing highly efficient bifunctional catalysts for the oxygen reduction and oxygen evolution reaction (ORR/OER) can open possibilities for future zinc air batteries (ZABs). Herein, cost-effective and highly conductive few-layer ferric and nickel chloride co-intercalated graphite intercalation compounds (FeCl3 -NiCl2 -GIC) are designed as bifunctional oxygen catalysts for ZAB. The optimized few-layer FeCl3 -NiCl2 -GIC catalyst exhibits a small overpotential of 276mV at 10mA cm-2 for the OER and achieves a high onset potential of 0.89V for the ORR. The theoretical analysis demonstrates the electron-rich state on the carbon layers of FeCl3 -NiCl2 -GIC during the catalytic process favors the kinetics of electron transfer and lowers the absorption energy barriers for intermediates. Impressively, the ZAB assembled with few-layer FeCl3 -NiCl2 -GIC catalyst displays a 160 h cycling stability and a high energy efficiency of 72.6%. This work also suggests the possibility of utilizing layer electronic structure regulation on graphite intercalation compounds as effective bifunctional catalysts for ZABs.

Graphitic carbon nitride-derived high lithium storage capacity graphite material with regular layer structure and the structural evolution mechanism

A novel graphite anode (Ni-g-C3N4) is synthesized by using graphitic carbon nitride as the precursor and nickel (Ni) as the catalyst, which dramatically decreases the reaction temperature to 850 °C. The critical role of Ni in denitrifying g-C3N4 to produce high-quality graphite is identified, with the results showing that the nitrogen content decreases from 62.1% to 1.2% and thus leading to greatly enhanced electrical conductivity as well as excellent rate capability, cycle performance and structure integrity. The Ni-g-C3N4 exhibits typical low voltage plateau characteristic of graphite anode and the transformation of graphite intercalation compounds are investigated in the in-situ XRD analysis during the discharge/charge process. The capacity retention is as high as 99.3% after 600 cycles at 0.5 A⋅g−1, demonstrating excellent structural stability. Moreover, the evolution from g-C3N4 to graphite Ni-g-C3N4 is investigated via TG-MS and high-temperature in-situ XRD, which clearly reveals that the catalytic graphitization processes mainly consist of the dissolution, re-precipitation and carbide conversion, along with the formation of intermediate Ni3C and the release of nitrogen gas. In general, this work not only proposes a novel method to synthesize high performance graphite anode from g-C3N4 for lithium ion batteries, but also unravels the catalytic graphitization mechanism.

Selective transport of water molecules through interlayer spaces in graphite

Interlayer space in graphite is impermeable to ions and molecules, including protons. Its controlled expansion would find several applications in desalination, gas purification, high-density batteries, etc. In the past, metal intercalation has been used to modify graphitic interlayer spaces; however, resultant intercalation compounds are unstable in water. Here, we successfully expanded graphite interlayer spaces by intercalating aqueous KCl ions electrochemically. Our spectroscopy studies provide clear evidence for cation-π interactions explaining the stability of the devices, though weak anion-π interactions were also detectable. The water conductivity shows several orders of enhancement when compared to unintercalated graphite. Water evaporation experiments further confirm the high permeation rate. There is weak ion permeation through interlayer spaces, up to the highest chloride concentration of 1 M, an indication of sterically limited transport. In these very few transported ions, we observe hydration energy-dependent selectivity between salt ions. These strongly suggest a soft ball model of steric exclusion, which is rarely reported. These findings improve our understanding of molecular and ionic transport at the atomic scale.

Site-Selective Surface Modification of 2D Superatomic Re6Se8.

Coating two-dimensional (2D) materials with molecules bearing tunable properties imparts their surfaces with functionalities for applications in sensing, nanoelectronics, nanofabrication, and electrochemistry. Here, we report a method for the site-selective surface functionalization of 2D superatomic Re6Se8Cl2 monolayers. First, we activate bulk layered Re6Se8Cl2 by intercalating lithium and then exfoliate the intercalation compound Li2Re6Se8Cl2 in N-methylformamide (NMF). Heating the resulting solution eliminates LiCl to produce monolayer Re6Se8(NMF)2-x (x ≈ 0.4) as high-quality nanosheets. The unpaired electrons on each cluster in Re6Se8(NMF)2-x enable covalent surface functionalization through radical-based chemistry. We demonstrate this to produce four previously unknown surface-functionalized 2D superatomic materials: Re6Se8I2, Re6Se8(SPh)2, Re6Se8(SPhNH2)2, and Re6Se8(SC16H33)2. Transmission electron microscopy, chemical analysis, and vibrational spectroscopy reveal that the in-plane structure of the 2D Re6Se8 material is preserved through surface functionalization. We find that the incoming groups control the density of vacancy defects and the solubility of the 2D material. This approach will find utility in installing a broad array of chemical functionalities on the surface of 2D superatomic materials as a means to systematically tune their physical properties, chemical reactivity, and solution processability.

High‐performance Li‐ion capacitor via anion‐intercalation process

AbstractSupercapacitors are characterized by their fast charge/discharge capability, high‐power capability, and long cycle life, but low‐energy‐density impedes their practical application. The requirement of achieving a highly efficient energy storage system demands the hybridization of supercapacitors and batteries. The anion‐intercalation chemistry of graphite with high insertion potential creates a possibility of using graphite as a cathode, which works as an acceptor‐type graphite intercalation compound. Herein, we report the reversible PF6– anion storage on the graphite cathode, which occurs by the combination of pseudocapacitive and diffusion‐limited redox reaction at a higher working potential. Furthermore, a dual carbon lithium‐ion capacitor (LIC) using commercial graphite as anion‐intercalation type, battery type cathode, and commercial‐activated carbon (AC) as supercapacitor type anode is designed. The assembled preanion intercalated Graphite/AC‐based LIC assembly displayed a high‐energy density of 90.73 Wh kg–1. Moreover, the device with low‐temperature stability is advantageous over traditional electrical double‐layer capacitors, mainly in terms of its energy and low cost with much more safety features than commercial lithium‐ion batteries.

Enhancing the coupling effect in a sandwiched FeNiPS3/graphite catalyst derived from graphite intercalation compounds for efficient oxygen evolution reaction

The FeNiPS3/GL sandwich-structure prepared via in situ transforming FeCl3-NiCl2-GIC exhibits excellent catalytic OER performance, which results from the coupling effect between FeNiPS3 and graphite layers facilitating electron transfer.

Graphite Intercalation Compounds (Gics) Based Multi-Functional Interface Layer Toward Highly Reversible Zn Metal Anodes

Graphite Intercalation Compounds (Gics) Based Multi-Functional Interface Layer Toward Highly Reversible Zn Metal Anodes

Magnesium/Lithium Hybrid Batteries Based on SnS 2 -MoS 2 with Reversible Conversion Reactions

The magnesium/lithium hybrid batteries (MLHBs) featuring dendrite-less deposition with Mg anode and Li-storage cathode are a promising alternative to Li-ion batteries for large-scale energy storage. However, their limited energy density limits their practical implementation. To improve this, beyond the commonly proposed intercalation compounds, high-capacity conversion-type cathodes based on heterostructures of tin sulphide-molybdenum disulphide (SnS 2 -MoS 2 ) are proposed in this work. Individual SnS 2 is already a promising high-capacity electrode material for multivalent batteries and undergoes conversion reactions during the ion storage process. The introduction of S-deficient MoS 2 enhances the reversibility of SnS 2 in the conversion reaction via strong polysulfide anchoring and catalytic effect. Our results show that the SnS 2 -MoS 2 electrode achieves a high charge capacity of ~600 mAh g -1 at 50 mA g -1 and an excellent rate capability of 240 mAh g -1 at 1000 mAh g -1 with a negligible capacity fading rate of 0.063% per cycle across 1000 cycles. The results highlight a new direction toward designing 2D heterostructures as high-capacity cathodes beyond intercalation-type cathodes for multivalent-ion batteries.