Intercalation Compounds Research Articles

Ion-exchange enabled new intercalation Li metal fluorides

Most metal fluorides-based Li ion battery cathodes suffer from large voltage polarization, volume change, slow rate, and capacity loss in battery cycling due to Li conversion reactions. Here we report a new type of intercalation Li metal fluorides obtained from Li/Na ion exchange of Na-intercalation compounds. The strategy enables a broad chemical design space of new intercalation compounds through the coupling of chemical and electrochemical synthesis pathways at drastically different temperatures. Both voltage plateau and cyclability can be tuned by composition control from chemical synthesis. Our Na/Li ion-exchange strategy thus opens the door to a family of intercalation Li metal fluorides that were not accessible previously due to conversion reactions of such compounds from direct chemical synthesis.

Co-Intercalation Batteries (CoIBs): The Use of TiS2 As Electrode for Solvent Co-Intercalation in Sodium-Ion Batteries

With the rising demand for lithium-ion batteries (LIBs), sodium-ion batteries (SIBs) have become an attractive alternative with the promise of improved safety, reduced cost, and lower environmental impact.1 However, the larger ion size of sodium cation has major consequence on the battery chemistry, which provides several challenges and opportunities for designing electrode materials and electrolyte solutions.2 Graphite is the currently most used anode material in LIBs. However, its use in SIBs, with traditional carbonate-based electrolytes, results in very poor specific capacities due to unfavorable thermodynamic processes.3 A strategy around this problem is to choose different solvents: Ethers and in particular glymes can exhibit a co-intercalation behavior into the graphite structure by forming ternary graphite intercalation compounds.4, 5 Although the co-intercalation of solvent molecules with sodium cation leads to a large increase in the graphite framework, the cycle life and rate capability of the reaction are excellent.Regardless of this, there is a lack of evidence for a comparable reaction with other electrode materials. Hence, it would be of interest to identify a cathode material that operates via this same mechanism. A battery based on solvent co-intercalation at both electrodes can have minimized charge-transfer resistances due to the absence of desolvation steps, and great cycle life. Thus, such a system can show high power density over many cycles. It has also been shown that stripping of the solvation shell can be the rate limiting step for battery operation, especially at subzero temperatures.6 Such a solvent co-intercalation battery (CoIB) could therefore be more energy efficient compared to other batteries or could enable a better low-temperature performance.Transition metal dichalcogenides (TMDs) have emerged as promising anode materials owing to their low cost, high electric conductivity, good thermal stability and environmental friendliness. Among them, titanium sulphide (TiS2), with a two-dimensional framework, exhibits several advantages such as a high conductivity (compare to other metal oxides), a larger interlayer distance (0.569 nm) compared to graphite (0.335 nm) and high stability. 7 Several papers have reported on the use of TiS2 as an anode material for SIBs, and observed that the voltage profiles and electrochemical behaviour of the system is highly dependent on the choice of electrolyte. However, this has seldomly been explicitly stated and the cause of the electrolyte dependence has never been investigated. By using operando and in-situ techniques such as Operando XRD and dilatometry, Na-diglyme complexes were showed to co-intercalate, similar as graphite, into TiS2. In contrast, no signs of solvent co-intercalation are observed in cyclic ethers and conventional carbonate-based electrolytes – where instead the redox reaction with TiS2 results in the formation of different NaxTiS2 compounds.As we identified TiS2 as “co-intercalation electrode” in glyme-based electrolytes it served to create the first ever solvent co-intercalation battery (CoIB – pronounced Co-IB) which was done by pairing TiS2 (positive electrode) with graphite (negative electrode).8 This work could enable the development of highly energy efficient batteries with minimum charge transfer resistances and References I. Hasa, S. Mariyappan, D. Saurel, P. Adelhelm, A. Y. Koposov, C. Masquelier, L. Croguennec and M. Casas-Cabanas, J. Power Sources, 2021, 482, 228872. P. Adelhelm, P. Hartmann, C. L. Bender, M. Busche, C. Eufinger and J. Janek, Beilstein Journal of Nanotechnology, 2015, 6, 1016-1055. B. Jache and P. Adelhelm, Angew. Chem., 2014, 126, 10333-10337. B. Jache, J. O. Binder, T. Abe and P. Adelhelm, Physical Chemistry Chemical Physics, 2016, 18, 14299-14316. M. Goktas, C. Bolli, J. Buchheim, E. J. Berg, P. Novák, F. Bonilla, T. f. Rojo, S. Komaba, K. Kubota and P. Adelhelm, ACS applied materials & interfaces, 2019, 11, 32844-32855. S. S. Zhang, K. Xu and T. R. Jow, Journal of Power Sources, 2003, 115, 137-140. Q. Yun, L. Li, Z. Hu, Q. Lu, B. Chen and H. Zhang, Adv. Mater., 2020, 32, 1903826. G. A. Ferrero, G. Avall, K. A. Mazzio, Y. Son, K. Janssen, S. Risse and P. Adelhelm, Adv. Energy Mater., 2022, 2202377. an improved low temperature performance, where the charge transfer can become rate limiting. Figure 1

(Invited) Carbon Nano-Onions: Potassium Intercalation and Reductive Covalent Functionalization

Functionalization of carbon nanomaterials is a promising approach to controllably engineer the band gap structure, create novel architectures, and manipulate the interfacial characteristics of graphene and carbon nanotubes, increasing their processability.[1,2] Herein we report the synthesis of covalently functionalized carbon nano-onions (CNOs) via a reductive approach using unprecedented alkali-metal CNO intercalation compounds. For the first time, an in situ Raman study of the controlled intercalation process with potassium has been carried out revealing a Fano resonance in highly doped CNOs. The intercalation was further confirmed by electron energy loss spectroscopy and X-ray diffraction. Moreover, the experimental results have been rationalized with DFT calculations. Covalently functionalized CNO derivatives were synthesized by using phenyl iodide and n-hexyl iodide as electrophiles in model nucleophilic substitution reactions. The functionalized CNOs were exhaustively characterized by statistical Raman spectroscopy, thermogravimetric analysis coupled with gas chromatography and mass spectrometry, dynamic light scattering, UV–vis, and ATR-FTIR spectroscopies. This work provides important insights into the understanding of the basic principles of reductive CNOs functionalization and will pave the way for the use of CNOs in a wide range of potential applications, such as energy storage, photovoltaics, or molecular electronics.[3] [1] Abellán, G.; Schirowski, M.; Edelthalhammer, K. F.; Fickert, M.; Werbach, K.; Peterlik, H.; Hauke, F.; Hirsch, A. J. Am. Chem. Soc. 2017, 139, 5175.[2] Schirowski, M.; Abellán, G.; Nuin, E.; Pampel, J.; Dolle, C.; Wedler, V.; Fellinger, T. P.; Spiecker, E.; Hauke, F.; Hirsch, A. J. Am. Chem. Soc. 2018, 140, 3352.[3] M. E. Pérez-Ojeda, E. Castro, C. Kröckel, M. A. Lucherelli, U. Ludacka, J. Kotakoski, K. Werbach, H. Peterlik, M. Melle-Franco, J. C. Chacón-Torres, F. Hauke, L. Echegoyen, A. Hirsch, G. Abellán, J. Am. Chem. Soc. 2021, 143, 18997. Figure 1

Solvent Co-Intercalation for Electrochemical Energy Storage

One of the major differences between sodium- and lithium-ion batteries (SIBs and LIBs) is how the ions electrochemically react with graphite, where large amounts of lithium can be stored in the graphite galleries, but sodium cannot form thermodynamically stable, high capacity binary graphite intercalation compounds (b-GICs).[1] In 2014, however, it was discovered that graphite had a much greater capacity to reversibly store sodium-ions than previously thought – but only when using ether based electrolytes.[2] The increased storage capabilities in ether based electrolytes comes about by the formation of a ternary graphite intercalation compound (t-GIC), whereby the sodium-ion is intercalated along with it solvation shell. Thus, graphite can store solvated sodium-ions, but not bare ones. This unconventional mechanism is already known to occur for certain solvents, such as propylene carbonate, but was always thought to be accompanied by complete destruction of the graphite.[3]Since then, several studies have been conducted on electrochemical solvent co-intercalation for energy storage,[4] but the topic is still unexplored. Several fundamental questions have received quite conflicting answers – Especially with regards to the SEI and the reaction mechanism - the system displaying both clear staging in graphite, with at least one well defined plateau for stage I formation, but also large pseudocapacitive features. Following development on electrochemical double-layers and confined electrolytes,[5] it appears in systems where reversible electrochemical co-intercalation occurs the system will display both clear faradaic and non-faradaic properties. This is indeed what is seen, as the system offers a moderate amount of energy density, similar to batteries, while still being highly reversible and extremely fast, even at low temperatures, similar to capacitors.[6,7] Moreover, the reaction is tunable by altering the electrolyte composition - opening up for a great deal of exploration.[8] These properties, along with using abundant materials, makes the system applicable to problems where both the properties of capacitors and batteries are needed, such as in grid storage.This talk purport to summarize our research activity on electrochemical solvent co-intercalation phenomena, ranging from fundamental questions such as how to detect solvent co-intercalation, to the nature of the electrochemical reaction. We also present our work on using solvent co-intercalation in full cells, as well as a new type of battery where both the anode and cathode operate by a solvent co-intercalation mechanism – the solvent co-intercalation battery (CoIB).[9] References [1] O. Lenchuk, P. Adelhelm, D. Mollenhaur, Phys. Chem. Chem. Phys., 21 (2019) 19378-19390.[2] B. Jache, P. Adelhelm, Angewandte Chemie, 126 (2014) 10333-10337.[3] K. Xu, Chemical reviews 104 (2004), 4303-4418[4] J. Park, Z-L. Xu, K. Kang, Frontiers in Chemistry, 8 (2020), 2296-2646[5] S. Fleischmann, Y. Zhang, X. Wang, P. T. Cummings, J. Wu, P. Simon, Y. Gogotsi, V. Presser, V. Augustyn, Nature Energy, 7 (2022),222-228.[6] J. Chen, Y. Peng, Y. Yin, Z. Fang, Y. Cao, Y. Wang, X. Dong, Y. Xia, Angew. Chem. Int. Ed. 60 (2021) 23858.[7] Z-L. Xu, G. Yoon, K-Y. Park, H. Park, O. Tamwattana, S. J. Kim, W. M. Seong, K. Kang, Nat. Commun. 10 (2019) 2598.[8] B. Jache, J. O. Binder, T. Abe, P. Adelhelm, Phys. Chem. Chem. Phys., 18 (2016) 14299-14316[9] G. A. Ferrero, G. Åvall, K. A. Mazzio, Y. Son, K. Janßen, S. Risse, P. Adelhelm, Adv. Energy Mater. 12 (2022) 2202377

Reversible Iron Oxyfluoride (FeOF)-Graphene Composites as Sustainable Cathodes for High Energy Density Lithium Batteries

Two large barriers are impeding the wide implementation of battery electric vehicles, namely driving-range and cost, primarily due to the low specific capacity/energy and high cost of mono-valence cathodes (e.g. LiNi0.8Co0.1Mn0.1O2) used in lithium-ion batteries. Iron is the ideal element of choice for cathode materials considering its abundance, low cost and toxicity. Two fundamental challenges, in particular, the poor reversibility of (de)lithiation and low electronic conductivity, prevent those iron based high specific capacity/energy multi-valence conversion cathodes from practical applications. In this work, we have developed a sustainable FeOF nanocomposite with extraordinary performance. In particular, we were able to reach the theoretical specific capacity of 621 mAh·g-1 and 1,124 Wh·kg-1 specific energy (2.1-valence change/2.1 Li+ stored per unit) and more than 100 cycles with 80% capacity retention at 0.1C (realizing the reversible (de)lithiation), which is 3 times of the specific capacity, and 2 times of the specific energy of current mono-valence intercalation LiCoO2 respectively (i.e., 145 mAh·g-1 and 551 Wh·kg-1). This is the result of an effective approach, combing the nanostructured FeOF with graphene sheets to solve these challenges, realized by (1) making the (de)lithiation reversible by immobilizing FeOF nanoparticles and the discharge products of Fe nanoparticle and LiF over the graphene surface, and sandwiching them between graphene sheets to prevent them from migration and dissolution into electrolytes and (2) providing the inter-particle electric conductivity. In situ high energy synchrotron X-ray absorption spectroscopy (XAS) reveals that this new FeOF composite has a different but reversible (de)lithiation mechanism. Importantly, it demonstrated that introducing small amount of graphene can create new materials with desired properties, opening a new avenue for altering the (de)lithiation process. Such extraordinary performance represents a significant breakthrough in developing the sustainable conversion materials for replacing the intercalation compounds, eventually overcoming the driving range and cost barriers.

Dual-Protective Artificial Layer on Lithium Metal Anodes for Improved Electrochemical Performance – an in-Depth Morphological and Electrochemical Characterization

The energy density of traditional lithium ion batteries (LIB) based on graphite intercalation compounds as negative active material is approaching the theoretical limit and are restricting the increasing demand of high energy battery systems for various mobile and stationary applications.[1] Consequently, the implementation of active materials with high specific energies became prerequisite for future battery technologies. Therein, lithium metal is one of the most promising anode active materials to replace state-of-the-art graphite active materials, due to its high theoretical capacity and low electrode potential.[2]However, poor cycling performance, low Coulombic efficiency, and the uncontrollable Li dendrite growth during lithium electrodeposition/dissolution processes remain as predominant challenges.[3] Several approaches were proposed to eliminate dendrite formation by implementing a mechanically and electrochemically stable artificial solid electrolyte interphase or artificial protective coatings (aPC) by in-situ or ex-situ surface modifications.[4] These designed aPCs should feature an increased and uniform Li-ion flux, mechanical robustness and/or protection against electrolyte decomposition, during substantial volume changes upon electrodeposition/dissolution. However, aPCs fail to support long term cycling stability in lithium metal batteries since they cannot cover all requirements.[5] Therefore, it is crucial to design and understand dual- and multilayer system that address multiple aforementioned requisites.[6] In this contribution, a dual-protective artificial layer is constructed on Li metal by physical vapor deposition consisting of an intermetallic LiZn-layer, providing a uniform Li-ion flux, and an inorganic Li3N-layer, which is electron-blocking, thus reveal surface protective properties. In addition to electrochemical characterization, the Li electrodeposition/dissolution behavior was investigated by cryo-FIB/SEM analysis to unravel the mechanism behind the enhanced cycling stability in symmetrical Li||Li cells and cells with a layered oxide-based positive electrode.[1] R. Schmuch, R. Wagner, G. Hörpel, T. Placke, M. Winter, Nature Energy 2018, 3, 267.[2] J. Liu, Z. Bao, Y. Cui, E. J. Dufek, J. B. Goodenough, P. Khalifah, Q. Li, B. Y. Liaw, P. Liu, A. Manthiram, Y. S. Meng, V. R. Subramanian, M. F. Toney, V. V. Viswanathan, M. S. Whittingham, J. Xiao, W. Xu, J. Yang, X.-Q. Yang, J.-G. Zhang, Nature Energy 2019, 4, 180.[3] T. Placke, R. Kloepsch, S. Dühnen, M. Winter, Journal of Solid State Electrochemistry 2017, 21, 1939.[4] N. Delaporte, Y. Wang, K. Zaghib, Frontiers in Materials 2019, 6.[5] D. Lin, Y. Liu, Y. Cui, Nature Nanotechnology 2017, 12, 194.[6] S. Lee, K.-s. Lee, S. Kim, K. Yoon, S. Han, M. H. Lee, Y. Ko, J. H. Noh, W. Kim, K. Kang, Science Advances 2022, 8, 1.

(Invited) Interaction and Transformation of Defects during Sodium-Ion Intercalation

Non-equilibrium defects often dictate macroscopic functional properties of materials. In energy materials, dislocations and planar defects significantly modify reversibility and kinetics. Nevertheless, transient imperfections briefly appearing during ionic transport have been challenging to capture, limiting understanding of their life cycle and impact. I will present our recent operando x-ray diffraction, x-ray nanoimaging, and resonant x-ray scattering results in sodium-ion intercalation compounds. Three-dimensional coherent x-ray imaging reveals the transformation and self-healing of a metastable domain boundary, glissile dislocation loop, and stacking faults. I will also discuss structure-selective x-ray spectroscopy, which allows us to link the long-range order with redox reactions in layered oxides during intercalation. The presence of high dimensional defects in energy materials observed with operando nanoimaging suggest their abundance and highlights the importance of defect engineering for developing next-generation energy solutions.

In Operando Strain Evolution in Sodium Chromium Oxide Cathode for Na-Ion Batteries during Battery Cycling

Layer-structured Na intercalation compounds such as NaxMO2 (M=Co, Mn, Cr) have attracted much attention as cathode materials for sodium-ion batteries due to their high volumetric and gravimetric energy densities. Among them, NaCrO2 with layered rock salt structure is one of the promising cathodes since NaCrO2 has a desirable flat and smooth charge/discharge voltage plateau.1 In addition, NaCrO2 has the highest thermal stability at charged state which makes it a potentially safer cathode material.2 The NaCrO2 exhibits a reversible capacity of 110 mAh g-1 with good cycling performance.3 However, the transition metal oxide (TMO) cathode materials in NIBs undergo severe chemo-mechanical deformations which leads to capacity fade and poor cycling and is the limiting factor of NIBs. The electrochemical characterization and examination of the electrode structure were the primary focus of several investigations. To improve the lifespan and performance of electrode materials for Na-ion batteries, it is vital to comprehend how Na ions impact the chemo-mechanical stability of the electrodes.In this talk, we will discuss the driving forces behind the structural and interfacial deformations on NaCrO2 cathodes. Digital image correlation measurements were conducted to probe strain evolution in the electrode during cycling. The free-standing composite NaCrO2 electrode was used for stain measurements in custom-cell assembly. The battery was cycled against Na metal in 1 M NaClO4 in PC. The first part of the study involves structural and interfacial deformations in the lower voltage range of 2.3 V to 3.5 V where x<0.5 in NaxCrO2. And the second part focuses on the structural and interfacial deformations in the voltage range of 2.3 V to 4.7 V where x>0.5 in NaxCrO2. In the preliminary studies, we observed that the initial insertion of Na ions leads to negative strain evolution (contraction) in the electrode, followed by expansions in the electrode at a higher state of discharge. Similar phenomena are also observed during charge cycles, where extraction of Na results in an initial contraction in the electrode, followed by expansion at a higher state of charge. Understanding the mechanisms behind chemo-mechanical deformations will allow to tune structure & material property for better electrochemical performance.Acknowledgement: This work is supported by National Science Foundation’s (NSF) Faculty Early Career Development (CAREER) Program, 2142726.

Investigation of vapochromism of 3,3′,5,5′-tetramethylbenzidine-tetrasilicicfluormica intercalation compounds through visible diffuse reflection and powder X-ray diffraction

In this study, we synthesized intercalation compounds of 3,3′,5,5′-tetramethylbenzidine (TMB) and tetrasilicicfluormica (TSFM) via a commonly used cation exchange method with TMB2+/TSFM cation exchange capacity (CEC) ratios of 1.0, 2.0, 2.7, and 5.4. These materials were characterized using powder X-ray diffraction (XRD), X-ray fluorescence, thermogravimetric-differential thermal analysis, scanning electron microscopy, and visible absorption spectroscopy. The vapochromism of each sample was assessed directly from the exterior of the glass sample tube using diffuse reflectance spectroscopy. All specimens vacuum-dried at 50 °C appeared yellow but turned green under water vapor at TMB/CEC = 2.0, 2.7, and 5.4, and blue under acetonitrile vapor at all TMB/CEC ratios. The sample with TMB/CEC = 2.0, in particular, exhibited clear vapochromic effects towards water and acetonitrile. Methanol and formic acid induced color changes similar to that of water vapor but less intense, except at TMB/CEC = 2.0. The color of each sample faded upon exposure to gaseous ammonia, whereas ethanol, acetone, iodomethane, and nonpolar solvents did not induce any color changes. The powder XRD pattern suggested changes in the array structures of TMB in the interlayer spaces due to vapor exposure.

A fast and environment-friendly method for preparing nanopowders Mo through electro- desulfidation of MoS2 in LiCl melt

Fast–reaction rate production of Mo with energy-saving and environmental protection is important for industries. However, the present preparation of Mo by pyrometallurgical process in industry is challenging. Here we demonstrate a solution route through direct electro- desulfidation solid MoS2 at 973 K in LiCl melt with a fast and environment-friendly method. When the scan rate was 50 mV/s, the total reduction (0.5 mg MoS2 in the MCE.) time was less 16 s, and the peak current density was as high as 38 A/cm2 with reference to the geometric surface of the cavity (ca. 0.004 cm2)Nano molybdenum powder can be obtained on cathode and element sulfur on anode. The current efficiency was 95% and energy consumption was 1.02 kWh/kg- Mo. The details of the electro-desulfidation mechanism of solid MoS2 was also investigated by cyclic voltammetry, potentiostatic and constant voltage electrolysis. Accordingly, the electro-desulfidation mechanism may be speculated as followings: the intercalation compound containing Li+ (LixMoS2) was first generated and then LixMoS2 was reduced to nanometer Mo powder.

In Situ Pore Formation in Graphite Through Solvent Co‐Intercalation: A New Model for The Formation of Ternary Graphite Intercalation Compounds Bridging Batteries and Supercapacitors

AbstractFor Li‐ion and Na‐ion batteries, the intercalation behavior of graphite anodes is quite different. While Li‐ions intercalate, Na‐ions only co‐intercalate with solvent molecules from the electrolyte solution leading to ternary graphite intercalation compound (t‐GIC) formation along with an expansion of the graphite interlayer spacing to 1.2 nm. This large interlayer spacing represents a micropore with parallel slit geometry. Little is known about t‐GIC formation, but it is commonly believed that throughout the reaction the ion is accompanied by either a full or partial solvation shell. Here, it is elucidated for the first time, using two independent methods – mass measurements and electrochemical impedance spectroscopy – supplemented by operando microscopy, entropymetry and simulations, that the storage mechanism is far more complex. A new model for the electrochemical solvent co‐intercalation process is proposed: As soon as solvated ions enter, the graphite structure is flooded with free solvents, which are subsequently replaced by solvated ions. Close to full sodiation, few free solvents remain and structural rearrangement take place to reach the full storage capacity. Thus, t‐GICs represent a unique case of switchable microporous systems and hence appear as a bridge between ion storage in the bulk phase and in micropores, i.e., between batteries and supercapacitors.

Advancements and Prospects of Graphite Anode for Potassium-Ion Batteries.

Potassium-ion batteries (KIBs) have recently attracted considerable attention owing to their resource abundance, low cost and environmental friendliness. Graphite as a mature commercial anode material for lithium-ion batteries, has been proved as a promising anode candidate for KIBs by reversible forming potassium-graphite intercalation compounds. However, large volume expansion and sluggish K+ kinetics caused by the incompatibility between large radius of K+ and the small interlayer spacing of graphite, result in the poor cycle stability and rate performances, hindering its practical application. Extensive research efforts have focused on improving the potassium storage performance of graphite anodes. This review provides an overview of recent advances in addressing these challenges and optimizing the electrochemical performance of graphite anodes for KIBs. Various strategies to improve the electrochemical performance of graphite and graphitic carbon anodes, such as microcrystalline regulation, heteroatom doping, morphological adjustment, and coating modification, are discussed, while the critical issues and challenges associated with graphite anodes and the prospects for their advancement in KIBs are highlighted. The review offers valuable guidelines for rational structural design and promotes the commercial development of high-performance graphite anode materials for KIBs.

Na-catalyzed rapid synthesis and characterization of intercalated graphite CaC6

In this study, we conducted experiments on CaC6 for elucidating the Na-catalyzed formation mechanism and achieving rapid mass synthesis of graphite intercalation compounds (GICs). Rapidly synthesized CaC6 was characterized by analysis of its crystal structure and physical properties. We found that the formation of the reaction intermediate Na-GIC (NaCx, x ≈ 64) requires a larger amount of Na than is intercalated between the graphite interlayers. The requirement for excess Na may provide insights into the mechanism of Na-catalyzed GIC formation. A Na-to-C molar mixing ratio of 1.5–2.0:6 was suitable for the efficient formation of CaC6 under heat treatment at 250 °C for 2 h, and the catalytic Na remaining in the sample was demonstrably reduced to a Na:Ca ratio of approximately 3:97. The upper critical field Hc2 was enhanced approximately three times compared to those of previous reports. Based on X-ray diffraction and experimental parameter analysis, we concluded that the enhancement of Hc2 was attributed to the disordered stacking sequence in CaC6, possibly because of the rapid and low-temperature formation. Physical properties derived from specific heat measurements were comparable to those of high-quality CaC6, which is slowly synthesized using the molten Li–Ca alloy method. This study provides new avenues for future research and exploration in the rapid mass synthesis of GICs as practical materials, for applications such as battery electrodes and superconducting wires.

Peroxydisulfate activation using magnetic graphite intercalation compounds: A promising system for pharmaceuticals removal in treated wastewater matrix

The release of contaminants of emerging concern (CECs) from the effluents of municipal wastewater treatment plants (MWWTPs) into the environment is a major problem because of its influence on both the environment and human health. The Fenton system has been demonstrated to remove CECs from different aqueous matrices effectively. However, the Fenton system has been considered to be efficient at acidic pH, which hinders its application in MWWTPs. Herein, the Fenton-like oxidation catalyzed by iron species intercalated between carbon layers of graphite (as a recyclable catalyst) was studied to remove amoxicillin, as a model pharmaceutical, from effluents of MWWTPs. Response surface methodology (RSM) was used to optimize system parameters, including catalyst loading, peroxydisulfate (PDS) dosage, and reaction time. Amoxicillin removal in the proposed system reached more than 99% by utilizing a catalyst dosage of 2 g/L and 5 mM of PDS at neutral pH. Sensitivity analysis of model parameters indicated that the amoxicillin removal was highly sensitive to the dosage of the catalyst, while the model is less sensitive to PDS dosage and reaction time. The results indicated that the PDS activation employing magnetic graphite intercalation compounds could be used as a promising system for pharmaceutical removal from MWWTP effluents.

Structure and Dynamics of Graphite Intercalation Compounds Analyzed using in situ 4D-STEM.

Structure and Dynamics of Graphite Intercalation Compounds Analyzed using in situ 4D-STEM.

Transverse resistivity of acceptor graphite intercalation compounds

The temperature dependences of the transverse resistivity for acceptor intercalation compounds of different stages based on fine crystalline anisotropic graphite in the temperature range from 4.2 K up to 300 K are studied. The peculiarities of the transverse resistivity are analyzed in the terms of the Sugihara model, which assumes two mechanisms of conduction in the direction perpendicular to the graphite layers, namely the diffusive motion of the charge carriers along the graphite layers and the hopping conduction into the neighboring graphite layers. The possibility of the manifestation of quantum effects of the charge carriers’ weak localization and interaction in a low temperature transverse resistance is evaluated.

How to efficiently intercalate alkaline-earth metals into graphite using LiCl-KCl molten salts: An overview on the case of barium

In this paper, we present the three first stages currently known Ba-based Graphite Intercalation Compounds (GIC). They are synthesized using the LiCl-KCl molten salts method, which is especially efficient in order to help the intercalation of barium into the 2D graphitic galleries. According to the chosen reaction conditions, it is possible to obtain either the BaC6 binary compound or one of the two quaternary phases whose intercalated sheets contain simultaneously lithium, potassium and barium. By combining X-ray diffraction measurements and ion beam analyses for these compounds, their chemical formula is well established: Li0.2K0.6Ba0.35C6 for the α-phase, Li0.2K0.75Ba0.6C6 for the β one and BaC6 for the binary.The intercalated sheets of this last compound are single-layered. Its repeat distance reaches 529 pm and its 2D unit cell is hexagonal and commensurate with the graphene one with a parameter of 430.6 pm However, α- and β-phases are much more complex. For α- compound, the intercalated sheets are three-layered with an interplanar distance of 650 pm, while for β-phase, they are six-layered and the interplanar distance reaches 950 pm Both 2D unit cells are hexagonal, with a planar lattice parameter a of 1074 pm and 1280 pm respectively.Finally, a model of reaction mechanism is proposed, which breaks down the intercalation process into several steps: intercalation of lithium (LiC6), then replacement by barium (BaC6), next, formation of the β-phase, and ultimately its elimination to the benefit of the α one. Thus, this latter appears as the most stable GIC in this LiCl-KCl molten medium.

Preparation of expanded graphite with (NH4)2S2O8 and H2SO4 by using microwave irradiation

BackgroundIn recent years, many researchers have paid great attention to expanded graphite (EG) due to its excellent properties and potential applications. However, the preparation of EG usually consumes a lot of chemicals and energy and generates hazardous residues, such as heavy metal containing wastewater. The main purpose of this study was to develop a green method for the preparation of EGs. Methods(NH4)2S2O8 and H2SO4 were used for the chemical intercalation process and the microwave irradiation process was employed for the expansion of graphite intercalation compounds (GICs) to obtain EGs. The Fourier transform infrared spectroscopy (FTIR) and the scanning electron microscopy (SEM) were used to examine the changes in the material microstructures. Significant findingsThe results showed that the reactant proportion of graphite : (NH4)2S2O8 : H2SO4 equal to 1 : 5 : 5.5 was the most appropriate condition to prepare GICs, and the EGs with the highest expanded volume (∼267 L/kg) was obtained by treating the GICs with microwave irradiation at 500 W for 60 s. Under these conditions, the EGs had a long axial length and few breakages. Excessive levels of microwave irradiation impaired the EGs and then left a loose structure and damaged surfaces, thus greatly increasing the specific surface area.

Atomic Structures of Multiply-Folded Graphene Layers on Flat Substrates

We have systematically studied the energetics of multiply-folded graphene layers on flat substrates, by atomistic-scale simulations using the empirical potentials proposed by Tersoff and Lennard-Jones. We find that the atomic structures of doubly-folded graphene layers consist of 2 motifs (bulge and root) for small-sized folds, and 3 motifs (bulge, root, and stacked-layer) for large-sized folds. The transition between them is caused by the competition between the adhesion-energy gain due to layer stacking and the elastic-energy loss associated with membrane distortion. Such a qualitative change in the atomic structure with increasing the fold size is a noteworthy feature of multiple folding which has not been addressed. We also calculate four-fold or more folding of graphene layers, successfully explaining an atomic force microscopy image reported in an experiment. Interspaces of different sizes and Moiré patterns appear in the atomic structures of the folds, which we believe can be exploited to generate intercalation compounds and electron states with favorable properties.

Alkali metals induced stacking phase transition of graphite

It is well known that alkali metals can intercalate into graphite to form graphite intercalation compounds but the structural change of graphite induced by alkali metals has been paid less attention. Herein, we report that alkali metals (Li, Na, K) induce the phase transition from ABC-stacking (or 3R phase) to AB-stacking (or 2H phase) of graphite. Specifically, for the graphite powder containing ∼45% 3R phase in a mixed phase, the temperature needed to ensure a complete stacking phase transition is 600 °C, 500 °C or 350 °C, for Li, Na or K, respectively, much lower than that needed in bare annealing (1800 °C) while without these alkali metals. Simulations based on density functional theory (DFT) suggest that the charge transfer from alkali metals to graphene distinctly lowers the energy barrier of transition, explaining the different phase transition temperatures for these alkali metals.