Intercalation Host Research Articles

First-Principles Study of Spinel MgTiS2 as a Cathode Material

Spinel intercalation hosts are well known to to facilitate high rate capability and high voltage Li-ion batteries. A recent experimental study has shown that Mg can reversibly intercalate in spinel TiS2, demonstrating the viability of Li intercalation host crystal structures for Mg-ion batteries [Sun, X.; Energy Environ. Sci. 2016, 9, 2273−2277]. We report on a first-principles statistical mechanics study of Mg insertion into spinel TiS2, accounting for occupancy on both octahedrally and tetrahedrally coordinated interstitial sites. In contrast to Li-containing spinels, we predict mixed octahedral and tetrahedral site occupancy at nondilute Mg concentrations consistent with the recent experimental study of Sun et al. The onset of mixed occupancy is correlated with an increase in the spinel volume upon Mg insertion, which is more pronounced in MgxTiS2 than in its Li counterpart. The results in this study suggest that the degree of mixed occupancy could be controlled through the volume of the host with addi...

In Situ Acoustic Diagnostics of Particle-Binder Interactions in Battery Electrodes

Summary The high phase-transformation strain developed upon intercalation in the host particles of a composite battery electrode affects the polymeric binder network mechanically, deteriorating the electrode cycling performance. Here, electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) is used to demonstrate a new strain-accommodation mechanism, in high-strain NaFePO 4 /PVdF electrodes, via relaxation of the binder network surrounding the intercalation particles. Complete mechanical degradation of the polymer network occurs during long-term cycling of NaFePO 4 electrodes in aqueous solutions (hard and tough behavior). In contrast, in aprotic solutions, a softened binder easily accommodates the high transformation strain, ensuring excellent electrode cycling performance (soft and tough behavior). Quantification of the high-frequency viscoelastic properties of an operating composite electrode linked to the binder's fracture toughness ensures fast and facile screening of the optimal polymeric binder/electrolyte solution combinations. This methodology should be extremely important for optimization of cycling performance of Li-Si anodes undergoing huge volume changes during cycling.

New Iron-Based Intercalation Host for Lithium-Ion Batteries

The discovery of high-performance cathode materials is imperative for advances in current lithium-ion battery technology. Although extensive efforts have been focused on developing novel cathode materials, it has been a grand challenge to find candidates that can outperform state-of-the-art cathode materials such as layered, olivine, and spinel lithium transition-metal oxides. This issue arises because there are only a limited number of intercalation hosts with appropriate redox potential and lithium solubility. Here, we present a new iron-based intercalation host for lithium ion by exploring the “host formation reaction” from the nanocomposite of lithium and transition-metal compound hosts (i.e., LiF and FeO). Fluoride ions released from LiF decomposition during charging induce an unexpected phase transition of FeO to a new host structure of cubic-FeOF, a new polymorphic structure of FeOF that is different from the well-known rutile-FeOF. Cubic-FeOF electrode exhibits a higher redox potential (3.2 V) inc...

Stabilization of a Metastable Tunnel‐Structured Orthorhombic Phase of VO2 upon Iridium Doping

Metastable compounds accessible through kinetic stabilization or under conditions of constrained equilibrium represent a richly varied landscape of structures, properties, and function that are oftentimes entirely inaccessible in thermodynamic minima. The multiple redox states of vanadium and the ability to modulate the connectivity of vanadium and oxygen atoms yields a rich diversity of structures for binary vanadium oxides. Here, it is demonstrated that an orthorhombic quasi‐1D polymorph of VO2, characterized by extended tunnels with a rectangular cross‐section, can be stabilized through the substitutional doping of iridium on the vanadium sublattice. The obtained structure is considerably distorted from a previously reported paramontroseite mineral phase. The metastable phase is obtained in nanoplatelet form and is stable with respect to the energetically proximate monoclinic/rutile thermodynamic minima up to a temperature of 350 °C. The open framework structure and the accessibility of multiple redox states at the vanadium center suggests that the polymorph could potentially serve as an intercalation host. Beyond the solubility limit of iridium on the vanadium sublattice (1.28–3.15 at.% depending on the precursor concentration), metallic Ir nanocrystals are found to be homogeneously dispersed on the surfaces of the nanoplatelets indicating a strong interaction between the metal nanocrystals and oxide lattice.

Cover Feature: Alloying in an Intercalation Host: Metal Titanium Niobates as Anodes for Rechargeable Alkali‐Ion Batteries (Chem. Asian J. 3/2018)

Cover Feature: Alloying in an Intercalation Host: Metal Titanium Niobates as Anodes for Rechargeable Alkali‐Ion Batteries (Chem. Asian J. 3/2018)

Alloying in an Intercalation Host: Metal Titanium Niobates as Anodes for Rechargeable Alkali-Ion Batteries.

We discuss here a unique flexible non-carbonaceous layered host, namely, metal titanium niobates (M-Ti-niobate, M: Al3+ , Pb2+ , Sb3+ , Ba2+ , Mg2+ ), which can synergistically store both lithium ions and sodium ions via a simultaneous intercalation and alloying mechanisms. M-Ti-niobate is formed by ion exchange of the K+ ions, which are specifically located inside galleries between the layers formed by edge and corner sharing TiO6 and NbO6 octahedral units in the sol-gel synthesized potassium titanium niobate (KTiNbO5 ). Drastic volume changes (approximately 300-400 %) typically associated with an alloying mechanism of storage are completely tackled chemically by the unique chemical composition and structure of the M-Ti-niobates. The free space between the adjustable Ti/Nb octahedral layers easily accommodates the volume changes. Due to the presence of an optimum amount of multivalent alloying metal ions (50-75 % of total K+ ) in the M-Ti-niobate, an efficient alloying reaction takes place directly with ions and completely eliminates any form of mechanical degradation of the electroactive particles. The M-Ti-niobate can be cycled over a wide voltage range (as low as 0.01 V) and displays remarkably stable Li+ and Na+ ion cyclability (>2 Li+ /Na+ per formula unit) for widely varying current densities over few hundreds to thousands of successive cycles. The simultaneous intercalation and alloying storage mechanisms is also studied within the density functional theory (DFT) framework. DFT expectedly shows a very small variation in the volume of Al-titanium niobate following lithium alloying. Moreover, the theoretical investigations also conclusively support the occurrence of the alloying process of Li ions with the Al ions along with the intercalation process during discharge. The M-Ti-niobates studied here demonstrate a paradigm shift in chemical design of electrodes and will pave the way for the development of a multitude of improved electrodes for different battery chemistries.

Reticular V2O5·0.6H2O Xerogel as Cathode for Rechargeable Potassium Ion Batteries.

Potassium ion batteries (KIBs), because of their low price, may exhibit advantages over lithium ion batteries as potential candidates for large-scale energy storage systems. However, owing to the large ionic radii of K-ions, it is challenging to find a suitable intercalation host for KIBs and thus the rechargeable KIB electrode materials are still largely unexplored. In this work, a reticular V2O5·0.6H2O xerogel was synthesized via a hydrothermal process as a cathode material for rechargeable KIBs. Compared with the orthorhombic crystalline V2O5, the hydrated vanadium pentoxide (V2O5·0.6H2O) exhibits the ability of accommodating larger alkali metal ions of K+ because of the enlarged layer space by hosting structural H2O molecules in the interlayer. By intercalation of H2O into the V2O5 layers, its potassium electrochemical activity is significantly improved. It exhibits an initial discharge capacity of ∼224.4 mA h g-1 and a discharge capacity of ∼103.5 mA h g-1 even after 500 discharge/charge cycles at a current density of 50 mA g-1, which is much higher than that of the V2O5 electrode without structural water. Meanwhile, X-ray diffraction and X-ray photoelectron spectroscopy combined with energy dispersive spectroscopy techniques are carried out to investigate the potassiation/depotassiation process of the V2O5·0.6H2O electrodes, which confirmed the potassium intercalation storage mechanisms of this hydrated material. The results demonstrate that the interlayer-spacing-enlarged V2O5·0.6H2O is a promising cathode candidate for KIBs.

Mitigating Cation Diffusion Limitations and Intercalation-Induced Framework Transitions in a 1D Tunnel-Structured Polymorph of V2O5

The design of cathodes for intercalation batteries requires consideration of both atomistic and electronic structure to facilitate redox at specific transition metal sites along with the concomitant diffusion of cations and electrons. Cation intercalation often brings about energy dissipative phase transformations that give rise to substantial intercalation gradients as well as multiscale phase and strain inhomogeneities. The layered α-V2O5 phase is considered to be a classical intercalation host but is plagued by sluggish diffusion kinetics and a series of intercalation-induced phase transitions that require considerable lattice distortion. Here, we demonstrate that a 1D tunnel-structured ζ-phase polymorph of V2O5 provides a stark study in contrast and can reversibly accommodate Li-ions without a large distortion of the structural framework and with substantial mitigation of polaronic confinement. Entirely homogeneous lithiation is evidenced across multiple cathode particles (in contrast to α-V2O5 partic...

A Promising High-Voltage Cathode Material Based on Mesoporous Na3 V2 (PO4 )3 /C for Rechargeable Magnesium Batteries.

The lack of suitable high-voltage cathode materials has hindered the development of rechargeable magnesium batteries (RMBs). Here, mesoporous Na3 V2 (PO4 )3 /C (NVP/C) spheres have been synthesized through a facile spray-drying-annealing method, and their electrochemically desodiated phase NaV2 (PO4 )3 /C (ED-NVP/C) has been investigated as an intercalation host for Mg2+ ions. The obtained ED-NVP/C exhibits an average discharge voltage of around 2.5 V (vs. Mg2+ /Mg), higher than those of most previously reported cathode materials. In addition, it can deliver an initial discharge capacity of 88.8 mA h g-1 at 20 mA g-1 , with good cycling stability. Ex situ X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results demonstrate that the electrochemical reaction is based on an intercalation mechanism and shows good reversibility. Galvanostatic intermittent titration technique (GITT) data have revealed that the intercalation process involves a two-phase transition. The reported ED-NVP/C cathode material with high working voltage offers promising potential for application in RMBs.

High-Voltage Aqueous Magnesium Ion Batteries.

Nonaqueous rechargeable magnesium (Mg) batteries suffer from the complicated and moisture-sensitive electrolyte chemistry. Besides electrolytes, the practicality of a Mg battery is also confined by the absence of high-performance electrode materials due to the intrinsically slow Mg2+ diffusion in the solids. In this work, we demonstrated a rechargeable aqueous magnesium ion battery (AMIB) concept of high energy density, fast kinetics, and reversibility. Using a superconcentration approach we expanded the electrochemical stability window of the aqueous electrolyte to 2.0 V. More importantly, two new Mg ion host materials, Li superconcentration approach we expanded the electrochemical stability window of the aqueous electrolyte to 2.0 V. More importantly, two new Mg ion host materials, Li3V2(PO4)3 and poly pyromellitic dianhydride, were developed and employed as cathode and anode electrodes, respectively. Based on comparisons of the aqueous and nonaqueous systems, the role of water is identified to be critical in the Mg ion mobility in the intercalation host but remaining little detrimental to its non-diffusion controlled process. Compared with the previously reported Mg ion cell delivers an unprecedented high power density of 6400 W kg ion cell delivers an unprecedented high power density of 6400 W kg while retaining 92% of the initial capacity after 6000 cycles, pushing the Mg ion cell to a brand new stage.

Chemical Preintercalation of Bilayered Vanadium Oxide for Versatile, High Capacity Electrodes in Ion-Based Batteries

Chemical pre-intercalation is a wet chemistry method that allows for the insertion of positively charged inorganic ions into the crystal structure of electrode materials prior to electrochemical cycling. This synthetic methodology was proven to be efficient for layered electrode materials. In our work, we use bilayered vanadium oxide (δ-V2O5) as a high capacity intercalation host. Chemical pre-intercalation synthesis approach is based on a sol-gel process in which the vanadium oxide bilayers grow through a sequence of hydroxylation and condensation reactions. During this process, chemically preintercalated inorganic ions are added into the reaction mixture, directing formation of novel, metastable structures with controllable, large interlayer spacing. Post-synthesis treatment, such as aging, hydrothermal treatment, or annealing, can be used to further tune structure, composition, and electrochemical properties of the synthesized materials. This method can be utilized to investigate two distinct directions in electrochemical systems. First, the effect of pre-intercalation of electrochemically active, charge-carrying ions (for example Li+ for Li-ion batteries) into the open interlayer spacing of a layered host structure can be studied with the aim to understand if ionic mobility and specific capacity can be improved. We have previously demonstrated that chemical pre-intercalation of Na+ ions into the structure of bilayered vanadium oxide results in record high initial capacities above 350 mAh g-1 in Na-ion cells. This performance is attributed to the expanded interlayer spacing and predefined diffusion pathways achieved by the insertion of charge-carrying ions prior to cycling [1]. Second, the effect of pre-intercalation of electrochemically inactive, stabilizing ions (for example Mg2+ ions for Li-ion batteries) on electrochemical stability of the layered phase upon cycling in various ion-based systems can be determined. We have recently shown that d-V2O5 can be preintercalated with a range of inorganic ions, including alkali (Li+, Na+, K+) and alkali-earth (Mg2+and Ca2+) ions, via our chemical pre-intercalation approach [2]. By altering the pre-intercalated ion, the interlayer spacing of the synthesized materials can be controlled between 9.62 Å to 13.40 Å. A correlation between hydrated ionic radii and interlayer spacing was for the first time described [2]. We demonstrated that ion-stabilization can indeed be used to improve the electrochemical stability of the bilayered phase in Li-ion and Na-ion batteries and that larger interlayer spacing can lead to improved electrochemical performance. Doubly charged Mg-preintercalated δ-MgxV2O5, which has the largest interlayer spacing of 13.40 Å, shows the highest capacity retentions of 81.8% and 68.3% in Li-ion and Na-ion batteries, respectively. In this work, we will first present a systematic study of the effect of chemical pre-intercalation of charge-carrying ions in three alkali-ion intercalation-based energy storage systems (δ-LixV2O5 in Li-ion cells, d-NaxV2O5 in Na-ion cells, and δ-KxV2O5 in K-ion cells). The initial specific capacities vary depending on ion system, with δ-LixV2O5 material exhibiting a capacity of 250 mAh g-1 in Li-ion cells and δ-NaxV2O5 material exhibiting a capacity of 365 mAh g-1 in Na-ion cells, when cycled in 1.5 – 4.0 V vs. Li/Li+ and Na/Na+ range, respectively. The mechanism of charge storage differs depending on the charge-carrying ion, with Li-ion and Na-ion cells demonstrating predominantly pseudocapacitive behavior with the sloped shape of charge/discharge curves, and K-ion cells revealing diffusion limited intercalation processes characterized by distinct plateaus on charge/discharge curves. Therefore, K-preintercalated bilayered vanadium oxide was cycled in a voltage range of 2.0 – 4.3 V vs. K/K+ and demonstrated a capacity of 238 mAh g-1. Our results provide an insight on how the mobility of the charge carriers is affected by their size while the charge is maintained the same. Second, the role of chemical pre-intercalated non-cycling ions on electrochemical stability will be discussed. Indeed the larger fraction of chemically preintercalated stabilizing ions can create stronger bonds with the layers of the host material, thus improving its stability. But at the same time, additional positive charge held by stabilizing ions decreases the charge-storage capabilities of the electrode materials. Therefore, an optimum amount of the stabilizing ions need to be determined to achieve high capacity and high electrochemical stability simultaneously. We will demonstrate the effect of stabilizing ion content on electrochemical performance of δ-MgxV2O5 in alkali-ion intercalation-based energy storage systems. This work demonstrates the efficacy and versatility of the unique chemical pre-intercalation approach to synthesize a wide-range of high-capacity, advanced layered electrode materials with controllable electrochemical performance. Clites, M., B.W. Byles, Pomerantseva, E., Journal of Materials Chemistry A, 2016. 4(20), 7754.Clites, M.; Pomerantseva, E., in preparation, 2017.

(Invited) Using Intercalation Compounds for Electrochemical Water Desalination

Electrochemical desalination technologies offer benefits in both scalability and energy consumption relative to pressure-driven processes (e.g., reverse osmosis). Electrodialysis using gas-evolution electrodes that sandwich a series of ion-exchange membranes is the most used of such technologies to date, but alternative electrochemical technologies using electrosorptive interactions have gained significant research attention to date. For instance capacitive deionization (CDI) uses ion adsorption within solution-phase electric double layers to remove salt. Such technology has been applied readily in brackish water desalination. Alternatively, solid-state faradaic electrodes have also been used to remove salt from water through both intercalation and chemical conversion reactions. Specifically, the desalination battery used a Na-ion intercalation cathode paired with an Ag/AgCl conversion anode.1 Intercalation materials have also been used in conjunction with capacitive electrodes to produce a hybrid CDI configuration with enhanced salt adsorption capacity per unit mass of electrode material.2 Here we report on a desalination device in which cation intercalation host compounds (IHCs) of identical chemical composition are used in both electrodes, a concept originally referred to as Na-Ion Desalination (NID).3 While the use of the same IHC in both electrodes is impractical for battery use, we show through computational modeling3,4 and later confirm by experiments5 that desalination is possible with electrodes of identical composition. We show that this mode of desalination is most efficient if an anion exchange membrane (AEM) is used to suppress Na-ion transport between the electrodes, rather than an unselective porous separator used in Na-ion batteries.3 This concept, which we refer to presently as cation intercalation desalination (CID), can be employed with generic intercalation host compounds. In our original work we predicted the performance of CID using Na0.44MnO2 (NMO) and NaTi2(PO4)3 (NTP) intercalation electrodes, which exhibit sizable volumetric charge capacities and therefore produce substantial degree of desalination even for seawater level salt concentrations. Specifically, a Na0.44MnO2-based CID-cell with 0.5 mm-thick electrodes desalinated 700 mM NaCl influent by 63% while consuming only 50% more energy (0.74 kWh/m3) than thermodynamic minimum when cycled at C/2 rate. The high volumetric charge-capacity of Na-ion battery IHCs enabled 59–64% drop in influent salinity with water-recovery levels up to 80% and 95% for 700 mM and 70 mM influent, respectively. Prussian Blue Analogues (PBAs) are an alternative class of intercalation host compounds that have shown facile intercalation and long cycle life in a variety of aqueous cation batteries. We have modeled a particular PBA, Na2NiFe(CN)6 (NiHCF), in CID operation and show that, despite its low charge capacity relative to NMO and NTP, efficient desalination of seawater-level concentrations is possible in a range of CID device configurations.4 In addition a variety of electrochemical cell architectures were explored ranging from the use of flow-through electrodes and extending to electrodialysis stacks using intercalation electrodes.4 We observe that the distribution of ionic current within flow channels is biased toward the inlet when concentrate and diluate streams flow in the same direction (i.e., parallel-flow configuration), but these effects can be mitigated by flowing concentrate and diluate streams in opposing directions (i.e., in counterflow configuration). Finally, we report on experiments using porous electrodes containing redox-active NiHCF nanoparticles in a CID configuration.5 On the basis of active-material mass NiHCF-based CID cells are shown to achieve a salt adsorption capacity in excess of typical CDI cells. These results show potential for decreased energy consumption relative to CDI cells. Initial results with electrolyte influent containing mixtures of cations also reveal preferential adsorption of K+ over Na+.

Fast kinetics of magnesium monochloride cations in interlayer-expanded titanium disulfide for magnesium rechargeable batteries

Magnesium rechargeable batteries potentially offer high-energy density, safety, and low cost due to the ability to employ divalent, dendrite-free, and earth-abundant magnesium metal anode. Despite recent progress, further development remains stagnated mainly due to the sluggish scission of magnesium-chloride bond and slow diffusion of divalent magnesium cations in cathodes. Here we report a battery chemistry that utilizes magnesium monochloride cations in expanded titanium disulfide. Combined theoretical modeling, spectroscopic analysis, and electrochemical study reveal fast diffusion kinetics of magnesium monochloride cations without scission of magnesium-chloride bond. The battery demonstrates the reversible intercalation of 1 and 1.7 magnesium monochloride cations per titanium at 25 and 60 °C, respectively, corresponding to up to 400 mAh g−1 capacity based on the mass of titanium disulfide. The large capacity accompanies with excellent rate and cycling performances even at room temperature, opening up possibilities for a variety of effective intercalation hosts for multivalent-ion batteries.

Si- and Sn-containing SiOCN-based nanocomposites as anode materials for lithium ion batteries: synthesis, thermodynamic characterization and modeling

AbstractNovel nanocomposites consisting of silicon/tin nanoparticles (n-Si/n-Sn) embedded in silicon carbonitride (SiCN) or silicon oxycarbide (SiOC) ceramic matrices are investigated as possible anode materials for Li-ion batteries. The goal of our study is to exploit the large mass specific capacity of Si/Sn (3 579 mAh g−1/994 mAh g−1), while avoiding rapid capacity fading due to the large volume changes of Si/Sn during Li insertion. We show that a large amount (∼30–40 wt.%) of disordered carbon phase is dispersed within the SiOC/SiCN matrix and stabilizes the Si/Sn nanoparticles with respect to extended reversible lithium ion storage. Silicon nanocomposites are prepared by mixing of a polymeric precursor with commercial and “home-synthesized” crystalline and amorphous silicon. Tin nanocomposites, in contrast, are prepared using a single precursor approach, which allows the in-situ generation of Sn nanoparticles homogeneously dispersed within the SiOC host. The best electrochemical stability along with capacities of 600 – 700 mAh g−1 is obtained when amorphous/porous silicon is used. Mechanisms contributing to the increase of storage capacity and the cycle stability are clarified by analyzing elemental composition, local solid-state structures, intercalation hosts and Li-ion mobility. Our work is supplemented by first-principles based atomistic modeling and thermochemical measurements.

Evaluation of Multivalent Cation Insertion in Single- and Double-Layered Polymorphs of V2O5

Multivalent intercalation batteries have the potential to circumvent several fundamental limitations of reigning Li-ion technologies. Such batteries will potentially deliver high volumetric energy densities, be safer to operate, and rely on materials that are much more abundant than Li in the Earth's crust. The design of intercalation cathodes for such batteries requires consideration of thermodynamic aspects such as structural distortions and energetics as well as kinetic aspects such as barriers to the diffusion of cations. The layered α-V2O5 system is a canonical intercalation host for Li-ions but does not perform nearly as well for multivalent cation insertion. However, the rich V-O phase diagram provides access to numerous metastable polymorphs that hold much greater promise for multivalent cation intercalation. In this article, we explore multivalent cation insertion in three metastable polymorphs, γ', δ', and ρ' phases of V2O5, using density functional theory calculations. The calculations allow for evaluation of the influence of distinctive structural motifs in mediating multivalent cation insertion. In particular, we contrast the influence of single versus condensed double layers, planar versus puckered single layers, and the specific stacking sequence of the double layers. We demonstrate that metastable phases offer some specific advantages with respect to thermodynamically stable polymorphs in terms of a higher chemical potential difference (giving rise to a larger open-circuit voltage) and in providing access to diffusion pathways that are highly dependent on the specific structural motif. The three polymorphs are found to be especially promising for Ca-ion intercalation, which is particularly significant given the exceedingly sparse number of viable cathode materials for this chemistry. The findings here demonstrate the ability to define cation diffusion pathways within layered metastable polymorphs by alteration of the stacking sequence or the thickness of the layers.

Activating layered LiNi0.5Co0.2Mn0.3O2 as a host for Mg intercalation in rechargeable Mg batteries

Layered crystal structures are some of the most intensively studied intercalation hosts for guest ion insertion. For Mg insertion, layered transition metal sulfides or selenides have been used for reversible Mg intercalation; however, far less intercalation hosts have been found for layered oxides most likely because of the strong interaction between Mg2+ and the oxide host. Here, we demonstrate that layered LixNi0.5Co0.2Mn0.3O2 (NCM523), which is an important commercial electrode for Li-ion batteries but has been regarded as electrochemically inactive in rechargeable Mg batteries, can function as a reversible host for Mg2+ if water opens up the layers and screens the electrostatic interaction between Mg2+ and the host. Upon the formation of water-intercalated NCM523, the discharge capacity dramatically increases utilizing the multi-redox reaction of Ni2+/Ni3+/Ni4+, which exhibits an average voltage of ∼3.1V (vs. Mg/Mg2+) in rechargeable Mg batteries with an energy density of 589Whkg−1 in the first discharge.

Chemical Intercalations in Layered Transition Metal Chalcogenides: Syntheses, Structures, and Related Properties

Transition metal chalcogenides (TMChs) have recently attracted a great deal of interest in the chemical and physical research fields. These compounds have a common crystal structure: they usually consist of two-dimensional or quasi-two-dimensional layers stacked along the direction perpendicular to the layers. The combination between layers is generally by van der Waals interaction or weak chemical bonding, making the layered chalcogenides potential hosts for intercalation. Alkali metals, alkaline earths, rare earths, and organic groups or compounds can be intercalated into the structure as spacing layers, resulting in a variety of new compounds and exhibiting interesting physical and chemical properties. In this review, we introduce and summarize the latest advances in chemical intercalation and the role of these spacing layers in TMChs, and their relation to relevant properties. Especially, we focus on the developments of chemical intercalation in Fe chalcogenide superconductors to understand the effect...

MoS2 as a long-life host material for potassium ion intercalation

Electrochemical potassium ion intercalation into two-dimensional layered MoS2 was studied for the first time for potential applications in the anode in potassium-based batteries. X-ray diffraction analysis indicated that an intercalated potassium compound, hexagonal K0.4MoS2, formed during the intercalation process. Despite the size of K+, MoS2 was a long-life host for repetitive potassium ion intercalation and de-intercalation with a capacity retention of 97.5% after 200 cycles. The diffusion coefficient of the K+ ions in K x MoS2 was calculated based on the Randles–Sevcik equation. A higher K+ intercalation ratio not only encountered a much slower K+ diffusion rate in MoS2, but also induced MoS2 reduction. This study shows that metal dichalcogenides are promising potassium anode materials for emerging K-ion, K-O2, and K-S batteries.

Theoretical evaluation of electrochemical cell architectures using cation intercalation electrodes for desalination

Water scarcity is a dilemma facing much of the global population. Cation intercalation desalination (CID) cells, which use intercalation host compounds (IHCs) in combination with ion-exchange membranes (IEMs), could aid in addressing this challenge by treating saline water sources. Originally, the performance of such cells was predicted utilizing continuous flow of saline water through porous IHC electrodes. Here, we use two-dimensional porous-electrode theory with concentrated solution transport to evaluate the performance of various cell architectures where flow occurs through open flow channels (OFCs) when two IHC electrodes comprised of nickel hexacyanoferrate (NiHCF) are used to store Na+ ions. We show that, when two OFCs are used, cation exchange membranes (CEMs) are adjoined at flow-channel/electrode interfaces, and an anion exchange membrane (AEM) is arranged between flow channels, salt removal increases relative to the original design with flow-through (FT) electrodes. The IEM stacking sequence within such a membrane flow-by (MFB) cell is the fundamental repeat unit for electrodialysis (ED) stacks using many IEMs (CEM/AEM/…/CEM/AEM/CEM) with many diluate streams. Accordingly, we simulate the performance of such ED stacks using NiHCF IHCs, and we predict that salt adsorption capacity (per unit NiHCF mass) is amplified by twenty-fold relative to MFB and FT cells, while simultaneously decreasing 0.7M NaCl feed water to 0.2-0.3M within diluate streams. The generality of these findings is further supported by simulations using Na0.44MnO2 IHC instead of NiHCF. Thus, we propose the use of cation IHCs as alternatives to the gas-evolution reactions used in conventional ED.

P2- and P3-KxCoO2 as an electrochemical potassium intercalation host.

Reversible and topotactic potassium intercalation of P2- and P3-KxCoO2 electrodes is studied in non-aqueous K cells for the first time. They deliver a highly reversible capacity of 60 mA h g-1 in the voltage range 2.0-3.9 V accompanied by reversible phase transitions including potassium/vacancy orderings. The electrochemical properties and structural change of P2-KxCoO2 are compared to those of O2-LixCoO2 and P2-NaxCoO2.