Alkali Metal Intercalation Research Articles

Preparation of S-doped biochar with sodium thiosulfate as activator and sulfur source and its highly efficient adsorption for Hg2+

Sulfur-doped biochar (S4BC) was prepared with cherry kernel powder as carbon source, Na2S2O3 as sulfur source and chemical activator. Na2S2O3 can activate biochar through the reaction with carbon, intercalation of alkali metals and the generated gas rushing out of pores, and at the same time, active sulfur atoms are doped into biochar during pyrolysis. The physical and chemical properties of S4BC adsorbent were evaluated by various characterization techniques. The results show that S4BC calcined at 800 °C has huge specific surface area of 959.6 m2/g, developed pore structure, and high content of S (18.84 wt%). Moreover, due to the existence of sulfur and oxygen functional groups, S4BC-800 provides sufficient active sites for the adsorption of Hg2+. According to Langmuir model, the maximum adsorption capacity of S4BC-800 for Hg2+ is 724 mg/g at 313 K, and the adsorption speed is fast with excellent stability and reusability. The microfiltration membrane device based on S4BC-800 can effectively remove the low concentration of Hg2+ in the solution. In this study, a simple method for preparing SBC materials is developed, which is not only of great significance as an adsorbent for Hg2+, but also provides a new choice for the preparation of heteroatom-doped materials.

Strain-induced intercalation of alkali metals (Li、Na、K) into Gr/2H(1T)-MoS2 heterostructure

The MoS2/C heterostructure, characterized by sizeable interlayer spacing and good reversible capacity, exhibits excellent potential as an anode material for alkali metal ion batteries. Using first-principles calculations, we systematically analyzed the intercalation of alkali metals (Li, Na, and K) into graphene/2H(1T)-phase molybdenum disulfide (Gr/2H(1T)-MoS2) heterostructures under strain by lattice engineering. The results show that the 1T-phase heterostructure exhibits a higher intercalation energy for alkali metals than the 2H-phase heterostructure. Strain reduces the intercalation energy of the system, facilitating the intercalation of alkali metals into host materials. An 8% strain reduces the intercalation energy of Li in the 1T-phase heterostructure by 72.8%. To rationalize the results, we assessed the charge transfer between the alkali metal and the host material and studied the d-band and p-band centers as a function of strain. The findings confirm that strain significantly enhances the electrical properties of Gr/2H(1T)-MoS2 heterostructures, offering a novel approach to designing anodes for alkali metal ion batteries.

Computational Investigation of Carbon Based Anode Materials for Li- and Post-Li- Ion Batteries.

Due to its negligible capacity with respect to sodium intercalation, graphite is not suited as anode material for sodium ion batteries. Hard carbon materials, on the other hand, provide reasonably high capacities at low insertion potential, making them a promising anode materials for sodium (and potassium) ion batteries. The particular nanostructure of these functionalized carbon-based materials has been found to be crucially linked to the material performance. However, there is still a lack of understanding with respect to the functional role of structural units, such as defects, for intercalation and storage. To overcome these problems, the intercalation of Li, Na, and K in graphitic model structures with distinct defect configurations has been investigated by density functional theory. The calculations confirm that defects are able to stabilize intercalation of larger alkali metal contents. At the same time, it is shown that a combination of phonon and band structure calculations are able to explain characteristic Raman features typically observed for alkali metal intercalation in hard carbon, furthermore allowing for the quantification of the alkali metal intercalation inbetween the layers of hard carbon anodes.

Observation of novel in-gap states on alkali metal dosed Ti2O3 film

Alkali metal dosing has nowadays been extensively used in angle-resolved photoemission spectroscopy (ARPES) for the in situ surface electron doping of materials to provide access to the unoccupied states. This technique also gives rise to nontrivial physical phenomena, such as the appearance of quantum well states and effects due to alkali metal intercalation. Here, we uncovered a previously unobserved type of electronic behavior induced by alkali metal dosing. By employing ARPES to study the evolution of the electronic structure of the Ti2O3 thin film upon rubidium (Rb) dosing, we found that the electron chemical potential of the system remains unchanged throughout the process. Interestingly, a series of electron-like band dispersions first appear with Rb dosing. A further increase in the Rb dosage leads to the eventual disappearance of the electron-like bands and the emergence of a set of hole-like bands. Our finding enriches the phenomenology brought about by alkali metal surface dosing, suggesting a novel functionality of this popular surface doping technique.

Alkali metal bilayer intercalation in graphene

Alkali metal (AM) intercalation between graphene layers holds promise for electronic manipulation and energy storage, yet the underlying mechanism remains challenging to fully comprehend despite extensive research. In this study, we employ low-voltage scanning transmission electron microscopy (LV-STEM) to visualize the atomic structure of intercalated AMs (potassium, rubidium, and cesium) in bilayer graphene (BLG). Our findings reveal that the intercalated AMs adopt bilayer structures with hcp stacking, and specifically a C6M2C6 composition. These structures closely resemble the bilayer form of fcc (111) structure observed in AMs under high-pressure conditions. A negative charge transferred from bilayer AMs to graphene layers of approximately 1~1.5×1014 e−/cm−2 was determined by electron energy loss spectroscopy (EELS), Raman, and electrical transport. The bilayer AM is stable in BLG and graphite superficial layers but absent in the graphite interior, primarily dominated by single-layer AM intercalation. This hints at enhancing AM intercalation capacity by thinning the graphite material.

Alkaline Metal Intercalates of VSe2 by Electrochemical Intercalation

AbstractWe report on the series of the alkali metal intercalates of VSe2 synthesised by electrochemical means in an aqueous environment. For all alkali metals we find water‐conintercalated structures (stage I and stage II), of which only the sodium structure had been reported so far. The new structures are analyzed by powder X‐ray diffraction and Rietveld refinement. Their (meta‐)stability is investigated in terms of the open circuit potential, revealing the sensitivity towards oxygen. Except for the lithium intercalate these structures transform into water‐free alkali metal intercalates under vacuum. In addition, scanning electron microscopy reveals the impact of different electrochemical intercalation techniques yielding different intercalation rates. This paves the way for future single crystal investigations.

Unravelling the mechanisms behind oxidative transformations of vivianite and parasymplesite into previously not recognized materials with unexpected oxidation states of iron – a systematic review

AbstractIn this paper, we describe the mechanisms behind the oxidative transformation of vivianite and parasymplesite into formerly not recognized materials that could prove to be novel players in, for example, water splitting or alkali metal intercalation reactions. Based on a sophisticated interpretation of hydrogen‐bonded networks, we were able to identify those phases that have erroneously been classified and to present the crystalline end‐members of the corresponding oxidation chains.

Boosting the gas sensing performances of 2H–MoSe2 bilayer upon alkali metal intercalation: Insights from DFT calculations

Realizing the multilayer or bulk MoSe2 cross from indirect bandgap to direct bandgap has drawn increasing attention due to the more practically useable and novel optoelectronic properties. In this work, the feasibility to realize indirect-to-direct band gap transition by intercalating alkali metals into 2H–MoSe2 bilayer was explored and its effect on the gas adsorption performance was evaluated utilizing first-principles calculation. The calculated results show that only Li and Na can be stably intercalated into the interlayer of 2H–MoSe2 bilayer. And the intercalated alkali metals as n-type dopant can realize the band gap transition from indirect to direct of 2H–MoSe2 bilayer, which is mainly ascribed to the decoupled interlayer interaction and built-in electric field in 2H–MoSe2 bilayer. Additionally, the adsorption performance of reducing gases is basically unchanged, while that of oxidizing gases (NO, NO2 and O2) is gradually enhanced with the intercalation concentrations of alkali metals increasing. The enhancement in adsorption performance for oxidizing gases is mainly ascribed to an indirect-to-direct bandgap transition along with the built-in electric field along the z-axis of 2H–MoSe2 bilayer. Through alkali metal intercalation, this research can provide a new method for the design and synthesis of transition metal dichalcogenides with enhanced gas-sensing performances.

Prediction of superconductivity in Li, K, Ca, and Sr-intercalated blue phosphorene bilayer using first-principle calculations

Blue phosphorene is an interesting two-dimensional (2D) material, which has attracted the attention of researchers, due to its affluent physical and chemical properties. In recent years, it was discovered that the intercalation of alkali metals and alkaline earth metals in 2D materials may lead to conventional Bardeen–Cooper–Schrieffer (BCS) superconductivity. In this work, the electronic structure, phonon dispersion, Eliashberg spectral function, electron–phonon coupling (EPC), and the critical temperature of blue phosphorene bilayer intercalated by alkali metals (Li, and K) and alkaline earth metals (Ca, and Sr) for both AB and AC stacking orders are studied using the density functional theory and the density functional perturbation theory, within the generalized gradient approximation with van der Waals correction. The present work shows that the blue phosphorene bilayer is dynamically stable in AB stacking for Li and AC stacking for K, Ca, and Sr, and after intercalation, it transforms from a semiconductor to a metal owing to charge transfer between intercalated atoms and phosphorene. Furthermore, the EPC constant and the critical temperature are higher than those of 2D BCS-type superconductors. They are about 3 and 24.61 K respectively for K-intercalated blue phosphorene bilayer. Thus, our results suggest that blue phosphorene is a good candidate for a superconductor.

Ultralow diffusion barrier induced by intercalation in layered N-based cathode materials for sodium-ion batteries.

Sodium-ion batteries (SIBs) have attracted huge attention due to not only the similar electrochemical properties to Lithium-ion batteries (LIBs) but also the abundant natural reserves of sodium. However, the high diffusion barrier has hindered its application. In this work, we have theoretically studied the relationship between the strain and the diffusion barrier/path of sodium ions in layered CrN2 by first-principles calculation. Our results show that the strain can not only effectively decrease the diffusion barrier but also change the sodium diffusion path, which can be realized by alkali metal intercalation. Moreover, the diffusion barrier is as low as 0.04 eV with the Cs atoms embedding in layered CrN2 (Cs1/16CrN2), suggesting an excellent candidate cathode for SIBs. In addition, the decrease of the barrier mainly originated from the fact that interlayer electronic coupling weakened with the increase of interlayer spacing. Our findings provide an effective way to enhance sodium diffusion performance, which is beneficial for the design of SIB electrode materials.

Wet Synthesis of Graphene-Polypyrrole Nanocomposites via Graphite Intercalation Compounds

Graphene-polypyrrole (GP) nanocomposites were synthesized by a wet-way protocol using a graphite bisulfate (GBS) precursor. Consequently, GBS, a type of graphite intercalation compound, was prepared in the presence of concentrated sulfuric acid in the presence of a potassium periodate oxidizer. Three different types of graphite precursor with particle sizes of <50 μm, ≥150, ≤830 μm, and ≤2000 μm were used for this purpose. It was found that in the Raman spectra of GBS samples, the characteristic D band, which is caused by defects in the graphene layer, disappears. Therefore, the proposed synthesis protocol of GBS could be considered as a prospective intermediate stage in the preparation of graphene with low defect concentration. In contrast to alkali metal intercalation, the intercalation process involving anions with a relatively complex structure (e.g., HSO4−), which has been much less studied and requires further research. On the basis of the results obtained, structural models of graphite intercalation compounds as well as GP nanocomposites were discussed. The most relevant areas of application for GP nanocomposites, including energy storage and (bio)sensing, were considered. This work contributes to the development of cost-effective, scalable, and highly efficient intercalation methods, which still remain a significant challenge.

Borate-Based Compounds as Mixed Polyanion Cathode Materials for Advanced Batteries.

Rational design of new and cost-effective advanced batteries for the intended scale of application is concurrent with cathode materials development. Foundational knowledge of cathode materials' processing-structure-properties-performance relationship is integral. In this review, we provide an overview of borate-based compounds as possible mixed polyanion cathode materials in organic electrolyte metal-ion batteries. A recapitulation of lithium-ion battery (LIB) cathode materials development provides that rationale. The combined method of data mining and high-throughput ab initio computing was briefly discussed to derive how carbonate-based compounds in sidorenkite structure were suggested. Borate-based compounds, albeit just close to stability (viz., <30 meV at-1), offer tunability and versatility and hence, potential effectivity as polyanion cathodes due to (1) diverse structures which can host alkali metal intercalation; (2) the low weight of borate relative to mature polyanion families which can translate to higher theoretical capacity; and a (3) rich chemistry which can alter the inductive effect on earth-abundant transition metals (e.g., Ni and Fe), potentially improving the open-circuit voltage (OCV) of the cell. This review paper provides a reference on the structures, properties, and synthesis routes of known borate-based compounds [viz., borophosphate (BPO), borosilicate (BSiO), and borosulfate (BSO)], as these borate-based compounds are untapped despite their potential for mixed polyanion cathode materials for advanced batteries.

Single- and Multilayers of Alkali Metal Atoms inside Graphene/MoS2 Heterostructures: A Systematic First-Principles Study

Stacking various 2D materials in van der Waals heterostructures is a novel approach to design new systems, which can host alkali metal (AM) atoms to tune their electronic properties or store energy. Using state-of-the-art first-principles calculations, we systematically study the intercalation of the most widespread AMs (Li, Na, and K) into a graphene/MoS2 heterostructure. Contrary to the previous work on the intercalation of AMs into various heterostructures based on 2D materials, we consider not only single-, but also multi-layer configurations of AM atoms. We assess the intercalation energetics for various concentrations of AM atoms, calculate charge transfer from AM atoms to the host system, and show that although intercalation of AMs as a single layer is energetically preferable, multi-layer configurations can exist at high concentrations of AM atoms. We further demonstrate that the transition of the MoS2 layer from the H to T′ phase is possible upon Li intercalation, but not for Na or K. Our findings should help to better understand the behavior of heterostructures upon AM atom intercalation and may stimulate further experiments aimed at the tailoring of heterostructure properties and increasing the capacity of anode materials in AM ion batteries.

Revisiting Solution-Based Processing of van der Waals Layered Materials for Electronics.

Following the significant discovery of van der Waals (vdW) layered materials with diverse electronic properties over more than a decade ago, the scalable production of high-quality vdW layered materials has become a critical goal to enable the transformation of fundamental studies into practical applications in electronics. To this end, solution-based processing has been proposed as a promising technique to yield vdW layered materials in large quantities. Moreover, the resulting dispersions are compatible with cost-effective device fabrication processes such as inkjet printing and roll-to-roll manufacturing. Despite these advantages, earlier works on solution-based processing methods (i.e., direct liquid-phase exfoliation or alkali-metal intercalation) have several challenges in achieving high-performance electronic devices, such as structural polydispersity in thickness and lateral size or undesired phase transformation. These challenges hinder the utilization of the solution-processed materials in the limited fields of electronics such as electrodes and conductors. In the meantime, the groundbreaking discovery of another solution-based approach, molecular intercalation-based electrochemical exfoliation, has shown significant potential for the use of vdW layered materials in scalable electronics owing to the nearly ideal structure of the exfoliated samples. The resulting materials are highly monodispersed, atomically thin, and reasonably large, enabling the preparation of electronically active thin-film networks via successful vdW interface formation. The formation of vdW interfaces is highly important for efficient plane-to-plane charge transport and mechanical stability under various deformations, which are essential to high-performance, flexible electronics. In this Perspective, we survey the latest developments in solution-based processing of vdW layered materials and their electronic applications while also describing the field's future outlook in the context of its current challenges.

Electrochemical intercalation of alkali metal – Lewis bases adducts into layered structure of iron chalcogenides

The electrochemical intercalation of alkali metal – pyridine adducts into iron selenide matrix (FeSe0.98) was performed using galvanostatic conditions in two- and three-electrode setup. The system was examined using electrochemical impedance spectroscopy and analyzed with four-elements equivalent circuit, in which solution and charge transfer resistance, double layer capacitance, and Warburg impedance (diffusion) were identified. Charge transfer resistance was found to rise with increasing reaction time. X-ray powder diffraction analysis revealed elongation of the c axis as a result of intercalation and structural transition from primitive to body-centered unit cell in Na-intercalated system. Scanning electron microscopy with X-ray microanalysis, differential scanning calorimetry, and atomic emission spectroscopy confirmed introduction of guest species. Magnetic susceptibility measurements proved paramagnetic character of studied samples, with occurrence of transition to the superconducting state at around 9 ​K, similarly to the value observed in pure FeSe0.98.

The first progress of plasma-based transition metal dichalcogenide synthesis: a stable 1T phase and promising applications.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted attention as polymorphs depending on their phases (1T and 2H) when applying typical synthesis methods. The 2H phase is generally synthesised through chemical vapour deposition (CVD) on a wafer-scale at high temperatures, and many synthesis methods have been reported owing to their thermodynamic stability and semiconductor properties. By contrast, although the 1T phase is meta-stable with an octahedral coordination, thereby limiting the use of synthesis methods, the recent structural advantage in terms of the hydrogen evolution reaction (HER) has been emphasised. Despite this demand, no large-area thin-film synthesis method for 1T-TMDs has been developed. Among several strategies of synthesizing metallic-phase (1T) TMDs, chemical exfoliation (alkali metal intercalation) is a major strategy and others have been used for electron-beam irradiation, laser irradiation, defects, plasma hot electron transfer, and mechanical strain. Therefore, we suggest an innovative synthesis method using plasma-enhanced CVD (PECVD) for both the 1T and 2H phases of TMDs (MoS2 and WS2). Because ions and radicals are accelerated to the substrate within the sheath region, a high-temperature source is not needed for vapour ionisation, and thus the process temperature can be significantly lowered (150 °C). Moreover, a 4-inch wafer-scale of a thin film is an advantage and can be synthesised on arbitrary substrates (SiO2/Si wafer, glassy carbon electrode, Teflon, and polyimide). Furthermore, the PECVD method was applied to TMD-graphene heterostructure films with a graphene-transferred substrate, and for the first time, sequential metal seed layer depositions of W (1 nm) and Mo (1 nm) were sulfurized to MoS2-WS2 vertical heterostructures with Ar + H2S plasma. We considered the prospects and challenges of the new PECVD method in the development of practical applications in next-generation integrated electronics, HER catalysts, and flexible biosensors.

Revisiting Intercalation‐Induced Phase Transitions in 2D Group VI Transition Metal Dichalcogenides

Intercalation of alkali metals is widely studied to introduce a structural phase transition from 2H to 1T′ in 2D group VI transition metal dichalcogenides (TMDCs). This highly efficient phase transition method has enabled an access to a library of phases with novel physical and chemical properties attractive for functional devices and electrochemical catalysis. However, despite numerous studies that have predicted that charge doping mainly contributes to the structural phase transition in the intercalation process, a mechanistic understanding of the phase transition at the atomic level has not been fully revealed. Furthermore, the coupled effects of strain and other intrinsic or extrinsic factors on the intercalation‐induced phase transition have not been quantitatively determined. Herein, the progress of the intercalation‐induced phase transition is briefly overviewed and the knowledge gaps in the current understanding of phase transition and intercalation in 2D TMDCs are highlighted. To fully gain the microscopic picture of the intercalation‐induced phase transition, in situ multimodal probes to monitor the real‐time structure−property relationship during intercalation are suggested. The proposed research directions further direct material scientists to efficiently engineer phase transition pathways in 2D materials to explore novel functional phases.

Bulk O2 formation and Mg displacement explain O-redox in Na0.67Mn0.72Mg0.28O2

Summary O-redox in compounds with Li on the transition-metal layers (TML) has recently been attributed to the formation of molecular O2 on charge, trapped in the lattice. Here, we show that a similar process occurs for P2-Na0.67[Mn0.72Mg0.28]O2, which contains Mg2+ on the TML. The molecular O2 is identified by high-resolution RIXS and quantified by magnetometry, showing that it equates to the charge passed. This O2 is trapped in voids that are formed by Mg2+ out-of-plane displacement and Mn4+ in-plane disordering and is then reduced on discharge associated with a large voltage hysteresis. In contrast to compounds containing Li+ in the TML, in which the honeycomb ordering and the high-voltage plateau are irreversibly lost after the first cycle, in P2-Na0.67[Mn0.72Mg0.28]O2, the plateau reappears partially on the second charge due to the partial reversibility of Mn in-plane and Mg out-of-plane migration and the local reformation of the honeycomb ordering.

Superconductivity in metal intercalated graphite-like boron-carbon-nitrogen

Ternary B-C-N materials have been widely investigated during recent decades. Additionally, previous investigations have indicated that intercalation of alkali metal could induce superconductivity emerged in layer structure. Motivated by this strategy, we attempt to establish the bulk structure of K-BC2N and explore its related properties by using density functional theory calculations. Two stable phases of K-BC2N were identified with anticipated metallic feature. Therefore, we calculated electron-phonon coupling interaction of K-BC2N within Allen-Dynes modified McMillan equation. The results confirm that bulk K-BC2N is a phonon-mediated superconductor with estimated critical temperature of 3∼6 K, providing a feasible approach for design and synthesis new superconductor at atmospheric pressure.

Charging a Negatively Curved Nanographene and Its Covalent Network.

This study explores a bottom-up approach toward negatively curved carbon allotropes from octabenzo[8]circulene, a negatively curved nanographene. Stepwise chemical reduction reactions of octabenzo[8]circulene with alkali metals lead to a unique highly reduced hydrocarbon pentaanion, which is revealed by X-ray crystallography suggesting a local view for the reduction and alkali metal intercalation processes of negatively curved carbon allotropes. Polymerization of the tetrabromo derivative of octabenzo[8]circulene by the nickel-mediated Yamamoto coupling reaction results in a new type of porous carbon-rich material, which consists of a covalent network of negatively curved nanographenes. It has a specific surface area of 732 m2 g-1 and functions as anode material for lithium ion batteries exhibiting a maximum capacity of 830 mAh·g-1 at a current density of 100 mA·g-1. These results indicate that this covalent network presents the key structural and functional features of negatively curved carbon allotropes.