Intercalation Of Alkali Metal Ions Research Articles

First principles investigation of voltage, structure, ionic and electronic conduction of olivine and maricite NaMnPO4

Mn2+/Mn3+ redox couple is expected to provide high operating voltage, but the Mn-based orthophosphate is difficult to achieve stable and reversible (de)intercalation of alkali-metal ions. Using first principles calculations, we investigated the structure, voltage, ionic and electronic transport properties of olivine and maricite NaMnPO4, trying to unveil the factors affecting the electrochemical performance. Our calculations show that the energetically favored structure transforms from the electrochemically active olivine to the inactive maricite with the decrease of sodium. This is likely to cause Mn to occupy Na site, blocking the diffusion channel along b axis. Lattice strain was found to have significantly influence on the relative structural stability. Both compressive and tensile ac biaxial strains induce the olivine MnPO4 to be in an energetically stable state. The enhanced structural stability of desodiated phase may prevent the irreversible structural transformation, contributing to the stable and reversible (de)intercalation of sodium ions.

Interfacial configuration and interfacial regulation of electronic properties of MoS2 heterophase junctions

The transition of 1H-transition metal dichalcogenides (TMDCs) to 1H-1T’ heterophase junction can be induced by alkali metal ion intercalation, laser irradiation, electric-field-induced etc, but the interfacial configuration is complex and the effect of the interface on the properties of TMDCs heterophase junction is not well known. Herein, we propose two kinds of interface models, namely, steep interface and gradient interface. The properties of 1H–MoS2 and 1T′-MoS2 phases are well preserved in the steep interface model due to clean atomic interface. In the gradient interface model, the interface configuration is relatively complex, but we find that the defects at the interface can release the local strain to improve the stability of the system. Interestingly, it is found that the 1H-1T’ MoS2 heterophase junction with higher intensity of density of state at the Fermi level (N(EF)) is more stable among the gradient interface model. Finally, it is found that the atoms in the interface of 1H-1T’ MoS2 heterophase junction have the largest out-of-plane deformation due to lattice mismatch regardless of the steep interface model or the gradient interface model, and the key factor affecting the electronic properties of the 1H-1T’ MoS2 heterophase junction is the electronic states of the atoms at the interface. We believe that our research provides a theoretical scheme for the interface regulation to achieve the application of 1H-1T’ heterophase junction based on TMDCs.

Decoupling the Effect of Electrolyte Infiltration on the Intercalation of Alkali Metal Ions in Highly Oriented Pyrolytic Graphite

Diffusion coefficients of ion in graphitic materials are responsible for high-rate batteries. However, the complex electrochemical response presented a challenge to accurately measure the diffusion coefficient of alkali-metal ions in graphitic materials. Here we design a method to identify the diffusion coefficients of Li+ and Na+ in highly oriented pyrolytic graphite (HOPG) with and without presence of liquid electrolyte infiltration. The results reveal inherent high diffusivity of Li+ in HOPG (∼10−7 cm2·s−1), as compared to HOPG with electrolyte infiltration (∼10−8 cm2·s−1), while Na+ has almost no interlayer diffusion without solvent infiltration. The presence of electrolyte has different effect on the interlayer diffusion of Li+ and Na+.

Initiating Jahn–Teller Effect in Vanadium Diselenide for High Performance Magnesium‐Based Batteries Operated at −40 °C

AbstractPoor electronic and ionic conductivity of electrode materials at low temperatures of −20 °C and below has significantly impeded development of batteries for cold conditions. However, for the first time, layer‐structured metallic vanadium diselenide (1T‐VSe2) is reported as a cathode material for low‐temperature Mg2+/Li+ hybrid batteries. A high electronic conductivity and fast ion diffusion kinetics for 1T‐VSe2 are demonstrated at selected temperatures, and a very safe 1T‐VSe2/Mg battery for operation at temperatures to −40 °C. The battery exhibits 97% capacity retention over 500 cycles, which is better performance than reported Mg‐based batteries. The Jahn–Teller effect in compressed configuration is initiated in 1T‐VSe2 with the change of electronic state occurring on electrochemical intercalation of alkali metal ions. Using combined experiment and theory via operando synchrotron X‐ray diffraction, ex situ X‐ray absorption spectroscopy and DFT computation, it is confirmed that the weak Jahn–Teller distortion contributes significantly to fast‐overall kinetics, structural stability, and high electronic conductivity of the electrode. Understanding at an atomic level of the mechanism is demonstrated, that provides valuable guidance in designing high‐performance electrode materials for low‐temperature batteries.

Driving Force behind the Amorphization in the Crystalline Cathode Structures during Alkali Metal Ion Intercalation for Electrochemical Energy Storage

Development of cathode structures suitable for Na-ion and K-ion batteries is still one of the major challenges on the way to the design of next-generation alkali metal-ion batteries. Although Li, Na and K belong to the same alkali metal group with a single charge in their cation form, intercalation of Na+ and K+ ions in electrodes is difficult since ionic radii of Na+ (0.98 Å) and K+ (1.38 Å) are larger than that of Li+ (0.69Å). Intercalation of alkali metal ions results in volumetric expansions in the electrode structure. Even modest expansions in brittle cathodes can cause particle fracturing in a larger crystalline-size scale. Intercalation of larger ions can cause structural collapse and amorphization induced by continuous accumulation of strains and distortions. However, the lack of understanding behind the amorphization mechanisms in the crystalline electrodes upon ion intercalation materials hinders the development of electrode structures suitable for these large ions.In the first part of the talk, we will first report the utilization of in situ digital image correlation and in-operando X-ray diffraction (XRD) techniques to probe dynamic changes in the amorphous phase of iron phosphate during potassium intercalation1. A new experimental approach allows to monitor dynamic physical and structural changes in the amorphous phase of the electrodes. This method offers new insights to study mechanics of ion intercalation in the amorphous nanostructures.In the second part of the talk, we will discuss the electrochemical and mechanical response of the iron phosphate cathodes upon Li, Na and K ion intercalation. Strain evolution during Li and Na intercalation results in more linear dependence on the state of charge / discharge. However, strains generated in the electrode shows nonlinear behavior during insertion / extraction of K ions. Strain rate calculations showed that K ion intercalation results in a progressive increase in the strain rate, whereas Li and Na intercalation induce nearly constant strain rates2. Our results shows that strain rates are critical factor for the amorphization of the crystalline structure, rather than the absolute value of electrochemical strains. These observations provide a fundamental insight into the impact of alkali ions on the redox chemistry and associated chemomechanical deformations.Acknowledgement: This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences (Award number DE-SC0021251).

Alteration of oxygen evolution mechanisms in layered LiCoO2 structures by intercalation of alkali metal ions

Two oxygen evolution reaction (OER) mechanisms on layered lithium cobalt oxide (LiCoO2 and simply LCO) were demonstrated by inserting various alkali metal ions.

Electrochemical strain evolution in iron phosphate composite cathodes during lithium and sodium ion intercalation

Sodiation-induced electrochemical strain generation in composite iron phosphate (FePO4) host material is compared with lithiation-induced strain evolution. FePO4 composite materials are prepared by an electrochemical displacement technique using pristine composite LiFePO4 as the starting material. The composite FePO4 electrodes have identical composition, binder, conductive additives and particle morphology for both Na+ and Li+ ion intercalation. We employ digital image correlation to investigate potential-dependent mechanical changes in FePO4 host material during alkali-metal ion intercalation via cyclic voltammetry and galvanostatic cycling. The FePO4 electrode experience much larger strains during the first sodiation (∼2.40%) compared to the first lithiation (∼0.60%). Strains in the subsequent cycles slowly decreased and become more reversible upon both Na+ and Li+ ion intercalation. Analysis of strain derivatives during lithiation, delithiation and sodiation exhibit a single peak that coincide with the associated phase transformation. The relative expansion in the composite electrode during Na+ ion intercalation with respect to Li+ ion intercalation is much greater than the relative expansions in electrode cell volume reported by the previous diffraction studies. We hypothesize that amorphization and slower Na+ diffusion in the electrode can lead to additional strain development compared to Li intercalation. Our results provide new insights into the mechanics of alkali metal-ion intercalation in cathodes.

Electrochemically Li-intercalated TiO2 nanoparticles for High performance photocatalytic production of hydrogen

Alkali metal ion intercalation into TiO2 photocatalysts is a well-known method for obtaining enhanced photocatalytic properties. Herein, an effective electrochemical lithiation method is proposed for the synthesis of lithium-intercalated TiO2 nanoparticles (NPs) suitable for high performance photocatalytic production of hydrogen. The electrochemical lithiation of TiO2 induces partial reduction of Ti ions in the crystal lattices, which introduces additional energy states within the band edge of TiO2, resulting in the improved optical properties. Consequently, Li-intercalated TiO2 NPs exhibit almost 60-times improved hydrogen generation activity under both UV and visible light exposure compared to those of commercial TiO2 NPs (P25).

The influences of Mg intercalation on the structure and supercapacitive behaviors of MoS2

Metallic 1T MoS2 greatly benefits the supercapacitance of MoS2 due to its considerably higher conductivity as compared to semiconducting 2H MoS2. Alkali metals, such as Li, Na and K, are always used to prepare 1T MoS2 through intercalation of alkali metal ions into the interlayer of 2H MoS2. Nevertheless, the influences of the alkali-earth metals as the guest in the interlayer of MoS2 on its structure and electrochemical capacitor performance are rarely investigated. Herein, we introduced hydrated Mg ions as the guest into MoS2 nanosheets. The interlayer spacing was increased to 1.144 nm after the introduction of hydrated Mg ions, larger than that of the pristine MoS2 (0.620 nm) and restacking MoS2 (0.626 nm). The enlarged interlayer spacing can accommodate more ions during intercalation process. Moreover, the 1T phase concentration after the introduction of hydrated Mg ions was as high as ~ 90%, which benefits the charge transfer during the charging/discharging processes. Consequently, the specific capacitance of the MoS2 with Mg guest ions as well as the energy densities and power densities was greatly improved as compared to those of the restacking MoS2 or pristine MoS2 counterparts. The present work not only demonstrated a new strategy for engineering the physical properties and improving the electrochemical performance of MoS2 supercapacitor electrode through pre-intercalation of alkali-earth metal ions in the interlayer of MoS2, but also has directive significance for the design of other layered electrode materials for energy storage systems.

Novel preparation of high activity 1T-phase MoS2 ultra-thin flakes by layered double hydroxide for enhanced hydrogen evolution performance

In this study, 1T phase molybdenum disulfide Ultra-thin Flakes (1T-MoS2 UFs) with high HER activity was successfully prepared by spatial confinement of layered double hydroxides (LDHs). The growth of MoS2 tends to be thin layer and high 1T phase due to the binding force of LDHs, this novel strategy is different from other phase transition methods, like alkali metal ion intercalation, electron irradiation, and stress induction, etc. The 1T-MoS2 UFs were used as hydrogen evolution reaction (HER) catalysts, when current density is 10 mA/cm2, the potential (vs. RHE) is 254 mV and the Tafel slope is only 64 mV/dec under the optimal condition. The superior HER activity is due to highly active 1T phase and rich defects.

Rational Design and in-Situ Electrochemical Characterization of Low Dimensional Nanomaterials and Devices for Energy Storage

Developing high performance energy storage devices such as metal ion batteries and supercapacitors are important for portable electronics, vehicle electrification and smart grid, while developing techniques for electrochemical monitoring that offer higher spatial and temporal resolution would open up new ways to study electrochemical interfaces and reaction kinetics for further developing novel energy storage devices. In this talk, I will introduce our recently developed materials optimization strategies and techniques to address their critical performance parameters related to energy density, power density, cycle, calendar life, and realize electrochemical monitoring, which includes (1) development of wafer-scale large-scale, shape & strain-controlled deterministic one-dimensional material assembly technique[1], which can be used for fabrication of single crystal nano-/microscale electrochemical devices array for in-situ electrochemical probing[2]; (2) synthesis and in-situ TEM characterization of self-adaptive strain-relaxed structure with high-stretchy protective shells through homogeneously crumpling of 3D graphene electrode showing high specific capacity, fast charge-discharge rate and long cycling stability for high-energy lithium battery materials[3]; and (3) operando observation of coupled discontinuous–continuous transitions in a series of ion-stabilized intercalation cathode[4], showing that the continuous transition at the intralayer could inhabit the irreversible ion intercalation and the consequent irreversible phase transition, while the discontinuous transitions at the interlayer of layered cathode provides the rapid adjustments in diffusion channels for the fast charge and discharge[5]. Reference: Y. Zhao, J. Yao, C.M. Lieber, et al. Shape-controlled deterministic assembly of nanowires. Nano Letters 2016, 16.4, 2644.L. Mai, M. Yan, Y. Zhao. Track batteries degrading in real time. Nature 2017, 546.7659, 469Y. Zhao, J. Feng, X. Liu, et al. Self-adaptive strain-relaxation optimization for high-energy lithium storage material through crumpling of graphene. Nature Communications 2014, 5.Y. Zhao, C. Han, et al. Stable alkali metal ion intercalation compounds as optimized metal oxide nanowire cathodes for lithium batteries. Nano Letters 2015, 15.3, 2180.G. Zhang, T. Xiong, Y. Zhao. Operando observation of coupled discontinuous–continuous transitions in ion-stabilized intercalation cathode. Submitted.

Intercalation chemistry of graphite: alkali metal ions and beyond.

Reversibly intercalating ions into host materials for electrochemical energy storage is the essence of the working principle of rocking-chair type batteries. The most relevant example is the graphite anode for rechargeable Li-ion batteries which has been commercialized in 1991 and still represents the benchmark anode in Li-ion batteries 30 years later. Learning from past lessons on alkali metal intercalation in graphite, recent breakthroughs in sodium and potassium intercalation in graphite have been demonstrated for Na-ion batteries and K-ion batteries. Interestingly, some significant differences proved to exist for the intercalation of Na+ and K+ into graphite compared with the Li+ case. Such different host-guest interactions are unique depending on the host materials and electrolytes, which greatly contribute to a deeper understanding of intercalation-type electrode materials for next generation alkali metal ion batteries. This review summarizes significant advances from both experimental and theoretical calculations with a focus on comparing the intercalation of three alkali metal ions (Li+, Na+, K+) into graphite and aims to clarify the intimate host-guest relationships and the underlying mechanisms. New approaches developed to achieve favorable intercalation coupled with the challenges in this field are also discussed. We also extrapolate alkali metal ion intercalation in graphite to mono-/multi-valent ions in layered electrode materials, which will deepen the understanding of intercalation chemistry and provide guidance to explore new guests and hosts.

A Novel Composite Li3V2(PO4)3∥Li2NaV2(PO4)3/C as Cathode Material for Li-Ion Batteries

A novel composite cathode for lithium ion batteries, Li3V2(PO4)3‖Li2NaV2(PO4)3/C, was synthesized by a sol-gel method. Cetyltrimethylammonium bromide (CTAB) was used as a surfactant while polyvinylidene difluoride (PVDF) was the carbon source. X-ray diffraction (XRD) and Raman results showed that the components of this composite are monoclinic Li3V2(PO4)3, rhombohedral Li2NaV2(PO4)3 and an amorphous carbon-coating. Four potential plateaus occur at the charge/discharge curves and the longest plateau is observed at a potential of 3.8/3.7 V. Therefore, the alkali metal ion intercalation and deintercalation mostly occur at this potential, which is different to that observed for Li3V2(PO4)3. In addition to the stable working potential, this composite also possesses an outstanding electrochemical performance. The sample containing 8.32 % carbon content delivers a capacity of 119 mAh g−1 at 0.2 C rate and 87 mAh g−1 at 12 C. After 50 charge/discharge cycles at 1 C, a coulombic efficiency of 98.4 % is maintained. This enhancement of the electrochemical performance could be attributed to the synergistic effect between monoclinic Li3V2(PO4)3 and rhombohedral Li2NaV2(PO4)3.

Hierarchical VS2 Nanosheet Assemblies: A Universal Host Material for the Reversible Storage of Alkali Metal Ions.

Reversible electrochemical storage of alkali metal ions is the basis of many secondary batteries. Over years, various electrode materials are developed and optimized for a specific type of alkali metal ions (Li+ , Na+ , or K+ ), yet there are very few (if not none) candidates that can serve as a universal host material for all of them. Herein, a facile solvothermal method is developed to prepare VS2 nanosheet assemblies. Individual nanosheets are featured with a few atomic layer thickness, and they are hierarchically arranged with minimized stacking. Electrochemical measurements show that VS2 nanosheet assemblies enable the rapid and durable storage of Li+ , Na+ , or K+ ions. Most remarkably, the large reversible specific capacity and great cycling stability observed for both Na+ and K+ are extraordinary and superior to most existing electrode materials. The experimental results of this study are further supported by density functional theory calculations showing that the layered structure of VS2 has large adsorption energy and low diffusion barriers for the intercalation of alkali metal ions.

Intermediate phases in sodium intercalation into MoS2 nanosheets and their implications for sodium-ion batteries

Alkali metal ion intercalation into layered transition-metal dichalcogenide structures is a promising approach to make next generation rechargeable batteries for energy storage. It has been noted that the number of Na-ions which can be reversibly intercalated and extracted per MoS2 is limited, and the chemical and electrochemical processes/mechanisms remain largely unknown, especially for nano-sized materials. Here, sodiation of MoS2 nanosheets are studied by in-situ electron diffraction and the phase transformations in sodiation are identified with the aid of DFT calculations to reveal the reaction mechanism. Several thermodynamically stable/metastable structures are identified in the sodiation pathway of MoS2 nanosheets, previously unnoticed in bulk MoS2. The gradual reduction of Mo4+ upon Na-ion intercalation leads to a transition of the Mo-S polyhedron from a trigonal prism to an octahedron around 0.375 Na per MoS2 inserted (i.e. Na0.375MoS2). When the intercalated Na-content is larger than 1.75 per MoS2 structural unit (i.e. Na1.75MoS2), the MoS2 layered structure collapses and the intercalation reaction is replaced by an irreversible conversion reaction with the formation of Na2S and metal Mo nanoparticles. The calculated sodiation pathways reproduce the experimental sodiation voltages. The current observations provide useful insights in developing sodium-ion batteries with high cycling stability.

Investigating the Intercalation Chemistry of Alkali Ions in Fluoride Perovskites

Reversible intercalation reactions provide the basis for modern battery electrodes. Despite decades of exploration of electrode materials, the potential for materials in the nonoxide chemical space with regards to intercalation chemistry is vast and rather untested. Transition metal fluorides stand out as an obvious target. To this end, we report herein a new family of iron fluoride-based perovskite cathode materials AxK1–xFeF3 (A = Li, Na). By starting with KFeF3, approximately 75% of K+ ions were subsequently replaced by Li+ and Na+ through electrochemical means. X-ray diffraction and Fe X-ray absorption spectroscopy confirmed the existence of intercalation of alkali metal ions in the perovskite structure, which is associated with the Fe2+/3+ redox couple. A computational study by density functional theory showed agreement with the structural and electrochemical data obtained experimentally, which suggested the possibility of fluoride-based materials as potential intercalation electrodes. This study inc...

Band-gap engineering with a twist: Formation of intercalant superlattices in twisted graphene bilayers

Graphene-based materials have long been considered as promising building blocks for a new generation of high-frequency (terahertz) electronic devices, but their use is complicated by the lack of an intrinsic band gap in graphene itself. Here we exploit synthetically controllable incommensuration of twisted graphene bilayers as a scaffold for intercalation of alkali metal ions with the periodicity of the bilayer supercell. Systematic exploration of the energy profiles of the ions as a function of position suggests that the alkali metal ions aggregate commensurately with the symmetry of the twisted bilayer. The intercalated alkali metal ions act as a source of a periodic perturbation on the level of the bilayer supercell, which permits opening and engineering of a band gap between graphene's \ensuremath{\pi} bands. The twist angle between the graphene layers determines the structure and disorder of the intercalant sublattice and, consequently, the magnitude of the band gap. Appropriate choices of the intercalant and twist angle thus permit band-gap engineering in graphene. We offer arguments that the impact of intercalation on the all important charge mobility of graphene will be rather small.

Stable alkali metal ion intercalation compounds as optimized metal oxide nanowire cathodes for lithium batteries.

Intercalation of ions in electrode materials has been explored to improve the rate capability in lithium batteries and supercapacitors, due to the enhanced diffusion of Li(+) or electrolyte cations. Here, we describe a synergistic effect between crystal structure and intercalated ion by experimental characterization and ab initio calculations, based on more than 20 nanomaterials: five typical cathode materials together with their alkali metal ion intercalation compounds A-M-O (A = Li, Na, K, Rb; M = V, Mo, Co, Mn, Fe-P). Our focus on nanowires is motivated by general enhancements afforded by nanoscale structures that better sustain lattice distortions associated with charge/discharge cycles. We show that preintercalation of alkali metal ions in V-O and Mo-O yields substantial improvement in the Li ion charge/discharge cycling and rate, compared to A-Co-O, A-Mn-O, and A-Fe-P-O. Diffraction and modeling studies reveal that preintercalation with K and Rb ions yields a more stable interlayer expansion, which prevents destructive collapse of layers and allow Li ions to diffuse more freely. This study demonstrates that appropriate alkali metal ion intercalation in admissible structure can overcome the limitation of cyclability as well as rate capability of cathode materials, besides, the preintercalation strategy provides an effective method to enlarge diffusion channel at the technical level, and more generally, it suggests that the optimized design of stable intercalation compounds could lead to substantial improvements for applications in energy storage.

New high-T c iron-selenide superconductor with hydroxide spacer layers

Iron-based superconductors include pnictides and chalcogenides. So far, the chalcogenides are much fewer in number, thus it is particularly valuable to find new superconductors in iron chalcogenides, for the “ultimate” understanding of iron-based superconductivity. The tetragonal binary iron selenide (β-Fe1+δSe) is the structurally simplest iron-based superconductor with a super-conducting critical temperature (Tc) of 8.5 K at ambient pressure. Under a hydrostatic pressure of ∼7 GPa, the Tc can be greatly enhanced to 37 K. By intercalation of alkali metal ions into adjacent iron-selenide layers, which induces more electrons into the FeSe layers, the Tc can also be increased to above 30 K. Upon applying high pressures around ∼12 GPa, an unknown secondary superconducting phase re-emerges at 48 K. Unfortunately, there exist phase separations in these intercalated compounds with only the minority phase responsible for superconductivity, which prevents revealing the intrinsic properties. Another remarkable progress is the observation of superconductivity in one-unit-cell FeSe thin film on a Sr-TiO3 substrate with impressively high Tc values up to 65 K and more recently exceeding 100 K. These findings inspire the exploration of high-Tc superconductivity in bulk FeSe-based materials.

Alkali Metal Intercalation in Curved Carbon Networks: X-Ray Structural Studies

The intercalation of alkali metal ions into carbon-based aromatic systems is of great interest in materials science due to the increased need for stable anode materials with high capacity of energy storage. Currently, graphite, a sp2-hybirdized carbon network, is the key anode component in rechargeable Li-ion batteries. Carbon allotropes with nonplanar π-surfaces, ranging from fullerenes to nanotubes, are now under investigation as prospective anode materials. The curved carbon networks of fullerenes and nanotubes are often modeled by open bowl-shaped polyaromatic hydrocarbons, such as the smallest curved fullerene fragment, corannulene (C20H10). One of the most fascinating properties of such bowl-shaped polyarenes and fullerenes is their ability to reversibly uptake and delocalize extra electrons upon multi-electron reduction without significant rearrangement and deformation of their carbon framework [1,2]. Notably, the anode material fabricated from corannulene shows a high reversible lithium capacity (602 mAh/g). This is almost twice as high as the theoretical capacity of the commonly used fully lithiated planar graphite material (LiC6, 372 mAh/g). In our work, we target the X-ray structural elucidation of metal intercalation patterns of carbon-rich curved polyarenes with light alkali metal ions, such as Li and Na, and compare those with extended planar polyaromatic systems. Recently, we expanded this study to the light alkaline earth metal, Mg, as its atomic radius is very close to that of Li. In addition, magnesium is cost effective and abundant, and thus presents great interest in the emerging energy storage technologies.