Monolayer Transition Metal Dichalcogenide Mo1-xWxS2 Alloys as

Subscriber access provided by University of South Dakota

C: Energy Conversion and Storage; Energy and Charge Transport

Monolayer Transition Metal Dichalcogenide Mo1-xWxS2 Alloys as Efficient Anode Materials for Lithium Ion Batteries Gayatree Barik, and Sourav Pal J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b07876 • Publication Date (Web): 26 Oct 2018 Downloaded from http://pubs.acs.org on October 29, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Monolayer Transition Metal Dichalcogenide Mo𝟏 - 𝐱𝐖𝐱𝐒𝟐 Alloys as Efficient Anode Materials for Lithium Ion Batteries Gayatree Barik1 and Sourav Pal1, 2* 1Department 2Department

of Chemistry, Indian Institute of Technology Bombay, Mumbai 400 076, India

of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur Nadia 741 246, West Bengal, India Email: [email protected]

ABSTRACT Intercalation of metal ions in the van der Waals gap of layered materials forms the basis for large scale electrochemical energy storage. In this work, by means of periodic density functional theory calculations, transition metal dichalcogenide Mo1 ― 𝑥𝑊𝑥𝑆2 alloys have been explored as efficient materials for lithium storage. Our study reveals that lithium prefers to bind efficiently to the monolayer alloy and diffuses easily with short diffusion distances. All bare phases of alloys are semiconducting and a semiconducting to metallic phase transition occurs after lithiation which ensures good electrical conductivity and is crucial for electrode material. We find negligible average open-circuit voltage (OCV), at different chemical stoichiometry of 0.67, 1.33 and 2. Effects of both strain and concentration on adsorption energy and diffusion barriers are calculated. Effect of strain has manifested significant rise in adsorption energy, whereas in case of diffusion barrier the effect is almost negligible and it remains close to the standard observed values. However, effect of concentration has yielded very optimistic results which are very close to the standard observed values in either case, concluding to negligible variations in both adsorption energy and diffusion barrier. All the superior properties including high adsorption energy, low diffusion barrier, low open-circuit voltage, high specific capacity and good electrical conductivity suggest that monolayer Mo1 ― 𝑥𝑊𝑥𝑆2 could be used as promising electrode materials in LIBs. 1. INTRODUCTION Electrochemical storage devices with high energy and power densities are most desirable for portable electronic devices. Lithium ion batteries (LIBs)1 have recently been the main sources 1 ACS Paragon Plus Environment

The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 34

of energy storage2 and the capability of LIBs is critically dependent on the reliability of their electrode materials. With an intention to achieve high energy and power densities of LIBs, development of innovative kind of materials has become evident.

3–8

Although graphene9 is

being widely used as an excellent electrode material, but its low theoretical capacity (372 mAhg−1) has clipped it to meet the growing demand of high power density.10,11 The arrival of layered nanostructure materials such as transition metal dichalcogenides (TMDs)11–16, has brought in a revolution in the field of electronics and optoelectronics17. The enhanced demand of graphene like ultrathin 2D transition metal dichalcogenides (TMDs) is because of high surface area, low diffusion distance, low cost, design flexibility, high electrical conductivity and flexible porous structure as well.18,19 Amongst all transition metals dichalcogenides (TMDs), molybdenum disulfide (MoS2)20– 22

and tungsten disulfide (WS2)23–25 are of paramount significance. This is due to their redundant

existence in different phases26,27 in contrast to other representative monolayer 2D materials, such as graphene and hexagonal boron nitride (h-BN), which do not exhibit different structural phases. It has been actively investigated that MoS2 posses high specific capacity.28 TMDs of ‘Mo’ and ‘W’ have been widely used in many areas. MoS2 has been used as a catalyst in hydrogen evolution reactions,29 and it has been observed that doping the material with other transition metal ions enhances the effectiveness of such catalyst. So strategy of doping and alloying30,31 provides a versatile way to tune the crystal structure and physical properties.32Alloying or doping of the TMDs permits permissible and accurate band gap tuning over a longer energy range. Alloying TMDs within the same transition metal group is conventionally possible because of the same lattice symmetry as well as only miniaturised mismatches.33 Possibility of synthesis of Mo1 ― 𝑥𝑊𝑥𝑆2 alloy with variation of x from zero to one has been proved theoretically and as well as experimentally.31,34,35 X-ray study indicates that Mo1 ― 𝑥𝑊𝑥𝑆2 compounds are synthesized proportionately from the constituent elements and crystallized in a layered type structure which exists in H phase.36 Recently metallic Mo1 ― 𝑥𝑊𝑥𝑆2 nano sheets have been synthesized with larger interlayer spacing which shows better HER performance.37 A systematic Raman spectral study for Mo1 ― 𝑥𝑊𝑥𝑆2 layered material synthesized by chemical vapour deposition (CVD) techniques were investigated for a variety range of composition with 0 ≤ x ≤ 1, which maintains hexagonal symmetry.38 The growth and study of 2D 2 ACS Paragon Plus Environment

Page 3 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


alloys with either transition-metal or chalcogen substitution, e.g. Mo1 ― 𝑥𝑊𝑥𝑆2 and MoS2𝑥Se2 ― 2𝑥 , have been studied extensively and were observed to be thermodynamically persistent at room temperature.39 Mo1 ― 𝑥𝑊𝑥𝑆2 alloy can be synthesized by sulfurization of Mo1 ― 𝑥𝑊𝑥𝑂𝑦 and spectroscopic results also indicate that the Mo1 ― 𝑥𝑊𝑥𝑆2 alloys have complete mixing of Mo and W atoms.40 Scanning transmission electron microscope images of Mo1 ― 𝑥𝑊𝑥𝑆2 quantitatively describes degree of alloying for both of the transition metal elements (Mo or W) and also provides a methodology for visualization of the atomic distributions.41 Recently, Qun et al.37 synthesized Mo1 ― 𝑥𝑊𝑥𝑆2 nano sheets which exhibit excellent cycling stability and outstanding HER behaviour with the lowest over potential. In-plane compressive strain induced structural transformation of 1T−1H phase of Mo1 ― 𝑥𝑊𝑥𝑆2 have been intensively explored by CVD growth and large-scale 1T−1H two-phase mono layers can be grown in a controllable manner by CVD.42 Although alloying of semiconducting material is a general phenomenon, there is still acute shortage of experimental and theoretical approaches for studying synthesis of an alloy of metallic character. There are sufficient strategies by which semiconducting to metallic phase transition is possible. Phase transition in monolayer MoS2 can be induced by alkali metal intercalation, strain, electron beam and laser beam irradiation.43–48 With the availability of all methods, intercalation method is one of the most widely accepted method to tune the crystal structure of the TMDs and it involves the intercalation of alkali metal ions in the van der Waals gap of the layered materials. This layered structure enables convenient intercalation and exfoliation of Li+ ions and involves structural phase transition. Brandt et al.49 suggested that a lithium molybdenum disulphide (Li𝑥MoS2) compound exhibits discrete phases when used as anode material in a battery. Many TMD materials with a single layer or few layers have been proposed to be used as electrode materials in LIBs both in and outside the laboratory, i.e. MoS2,28,50–53

VS2,

54,55

WS2,56 SnS2,57 SnS,58

MnO259 and Phsophorous60 which involves

intercalation method. Chang et al.61 synthesized nano flower of MoS2 by ionic liquid assisted hydrothermal reaction and that nano flower MoS2 exhibit a high reversible capacity of ~900 mAh/g. Recently, Wang et. al62 synthesized three layered TiO2-carbon-MoS2 tubular nanostructures by a sequential method which exhibits enhanced lithium storage properties in terms of high capacity, long cycle life, and dominant rate performance. Sun et al. obtained Mo2C monolayer as an appealing anode material for both lithium-ion and sodium-ion batteries.63 3 ACS Paragon Plus Environment


Recently Zhang et al.64 studied electrochemical reaction mechanism of MoS2 electrode in lithiumion cells and they found that intercalation reaction of MoS2 is reversible, which drives to a phase transformation between 2H and 1T phases. Cyanide bridged coordination compound Prussian Blue/MoS2 nano composite has been anticipated as a superior cathode material for Sodium- and Potassium-Ion Batteries.65 MoS2 is the most widely used material in the area of electrochemical energy storage66 because of its large interlayer distance that can dexterously intercalate different metal ions in between its layers and the exceptional properties of MoS2 can be augmented further to diversified compositions of Mo1 ― 𝑥𝑊𝑥𝑆2 to obtain more diverse electronic properties. So in order to assess the electronic structure of 2D Mo1 ― 𝑥𝑊𝑥𝑆2 alloys, understanding of phase transition properties are essential. In this work, we brought out the lithium adsorption properties of Mo1 ― 𝑥𝑊𝑥𝑆2 alloys, in lithium-ion Batteries. We have prepared four varying type of semiconducting Mo1 ― 𝑥 𝑊𝑥𝑆2 alloy with variation of x from zero to one. We have explored the adsorption of lithium on Mo1 ― 𝑥𝑊𝑥𝑆2 alloy by means of periodic density functional theory calculations. Our results indicate that, Li can be adsorbed on the surface of Mo1 ― 𝑥𝑊𝑥𝑆2 monolayer, maintaining the metallic nature of the system and layered Mo1 ― 𝑥𝑊𝑥𝑆2 shows higher adsorption energy of 1.48 to 1.78 eV for Li ion and a negligible Li diffusion barrier of 0.210-0.183 eV. The calculated negligible diffusion barriers imply a high mobility and good cycling ability of Mo1 ― 𝑥𝑊𝑥𝑆2 monolayer alloy, which is pivotal for the anode materials in LIBs. So Mo1 ― 𝑥𝑊𝑥𝑆2 alloy could provide a new class of electrode materials for lithium-ion batteries. 2. COMPUTATIONAL DETAILS All evaluations are carried out by plane-wave based density functional theory (DFT) using Quantum-Espresso67 package. The exchange correlation interactions are described by generalized gradient approximation using Perdew−Burke−Ernzerhof functional68 including van der Waals (vdW) correction69 and electron−ion interactions are described by ultra soft pseudo potentials. An energy cut-off of 28 Ry is chosen for the plane-wave basis expansion for all the calculations. All atomic optimizations are performed with a criterion of convergence of 0.025 4 ACS Paragon Plus Environment

Page 4 of 34

Page 5 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


eV/Å. Brillouin zone integration is carried out with a 4 × 4 × 1 Monkhorst-Pack70 grid of k points for a 3 × 3 periodic super cell of Mo1 ― 𝑥𝑊𝑥𝑆2 alloy. To avoid interlayer interactions, a vacuum spacing of 20 Å is given in z-direction. Bader algorithm71 is used for determination of the charge transfer on the atoms. To study diffusion behaviour of Li on the surface of Mo1 ― 𝑥𝑊𝑥𝑆2 sheet and to determine the minimum energy pathways as well as for the energy barriers, the climbing image nudged elastic band (CI-NEB)72 method has been used. A series of intermediate image structures were inserted between the optimized initial and final structures. 3. RESULTS AND DISCUSSION 3.1. Adsorption of Li on a Monolayer Mo𝟏 ― 𝒙𝑾𝒙𝑺𝟐. In TMDs, each of the transition metal atom is coordinated to six chalcogen atoms with a triangular prismatic or octahedral structure. With the foundation of the coordination structure of the transition metal and the stacking sequence of MX2 layers, TMDs can be categorised into several phases including 1T and 2H, which are the widely prevalent phases. In the 2H phase, transition metal atoms are encircled by chalcogen atoms forming triangular prisms and MX2 layers are stacked in AA sequence. In the 1T phase, transition metal atoms are octahedrally coordinated, with the MX2 layers stacked in AB sequence. Amongst all TMDs, molybdenum disulfide (MoS2) have been extensively investigated as a versatile material in all fields such as optoelectronics, catalysis, and energy storage devices.53,73–75 Transition metal sulphides or selenides76 with transition metals in the same column of the periodic table have similar lattice constants and have same structure like MoS2 and WS2. Both MoS2 and WS2 exists in two different phases with completely different electronic properties such as 2H phase is semiconducting, where as 1T is metallic.77 Analogous to MoS2 and WS2, Mo1 ― 𝑥𝑊𝑥𝑆2 alloy has a layered structure, with each Mo/W atom is sandwiched between two hexagonal S atom layers. The optimised lattice parameters ‘a’ and ‘c’ obtained for both MoS2 and WS2 are equal 3.16 Å and 12.294 Å, which is in concurrence with previous reports.15 In contemporary days both MoS2 and WS2 have attracted much attention as electrode material for LIBs due to their high surface area and short diffusion 5 ACS Paragon Plus Environment


length and Li+ ions can be easily intercalated or extracted from these materials.56 The van der Waals gap

Figure 1: Four different type of alloys of monolayer transition metal dichalocogenide Mo1 ― 𝑥𝑊𝑥𝑆2. The blue, green, and yellow colours denote Mo, S, and W atom respectively.

between the layers provides a conducive environment for accommodation of Li+ ions. In the subsequent study, we institute intercalation of lithium atoms on the surface of 2D Mo1 ― 𝑥𝑊𝑥𝑆2 alloy to induce phase transition, which is a typical procedure for the intercalation/deintercalation processes in LIBs. Here we examine the adsorption and diffusion of lithium on the hexagonal Mo1 ― 𝑥𝑊𝑥𝑆2 monolayer with variation of x for 0.00, 0.33, 0.66, and 1.00. Engineering the phase of Mo1 ― 𝑥𝑊𝑥𝑆2 monolayer alloy is both fundamentally incredible and technically significant.78 The four different alloys of Mo1 ― 𝑥𝑊𝑥𝑆2 are shown in figure 1. In both the cases of MoS2 and WS2, the TMo (top site of Mo) and TW site (top site of W) where Li is adsorbed just above the 6 ACS Paragon Plus Environment

Page 6 of 34

Page 7 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


metal atoms is more favourable for lithiation than the hollow site (HMo/W) where Li atom is located at the centre of hexagonal ring. Similar to Li adsorption on MoS2 28,78–81 and WS2, there are two adsorption sites for the Li atom, for Mo1 ― 𝑥𝑊𝑥𝑆2 alloy as shown in Figure S1. This has been observed for all TMDs alloy which has been taken into account for ion adsorption. Consequently we contemplate that all Li ions are adsorbed only at top sites to evaluate their stability. The adsorption energy ( Ea ) for Li ion is defined by the following formula: 𝐸𝑎 = 𝐸Mo1 ― 𝑥𝑊𝑥𝑆2 + 𝐸Li ― 𝐸Mo1 ― 𝑥𝑊𝑥𝑆2 ― Li Here 𝐸Mo1 ― 𝑥𝑊𝑥𝑆2 ― Li, 𝐸Mo1 ― 𝑥𝑊𝑥𝑆2 and 𝐸Li are the total energies of lithium adsorbed Mo1 ― 𝑥𝑊𝑥𝑆2 , pristine Mo1 ― 𝑥𝑊𝑥𝑆2 and the energy of an isolated Li atom respectively. Our results indicate that Li atom prefers to adsorb on the top site with the adsorption energy of 1.74 eV, in case of MoS2 and 1.44 eV for WS2 and for their alloys this adsorption energy varies in between 1.74 eV and 1.44 eV (Figure 2a). These results concur well with the past results.78,82 Identically, at hollow site adsorption energy is slightly lower than the adsorption energy on the top site. But in case of MnO2, Li adsorption at hollow site is more stable than top site,59 and same phenomena has also been observed with potassium intercalation on MoS2.83

7 ACS Paragon Plus Environment


Figure 2: Variation of Li Adsorption energies of Mo1 ― 𝑥𝑊𝑥𝑆2 with different compositions of x. (a) Adsorption energy at top and hollow site (b) Adsorption energy at single side and double sides of monolayer Mo1 ― 𝑥𝑊𝑥𝑆2 sheet.

The adsorption energy is 0.04 eV more stable at double side adsorption, which indicates that Li atoms prefer to adsorb on both sides of the Mo1 ― 𝑥𝑊𝑥𝑆2 sheet in comparison to single side84 (Figure 2b). Our calculated results show that before lithium intercalation, the optimized bond distance between Mo and S atoms dMo/W−S = 2.4 Å, the distance between two S atoms for both MoS2 and WS2 dS−S = 3.16 Å, and the angle between two Mo−S bonds θS−Mo−S = 81.07° (Table S1). After Lithium intercalation, the M-S distance increases to 2.46 Å and S-S distance increases to 3.21 Å. The distance between Lithium and metal remains 3.13 Å for MoS2 and 3.17Å for WS2 and S-Li distance remains 2.39 Å for MoS2 and 2.41 Å for WS2. Similarly, the angle between two Mo−S bonds θS−Mo−S increases from 81.07° to 81.32° for MoS2 and 81.20° for WS2. The adsorptions of Li at different distances are also calculated and the adsorption distance between the Li atom and the three affected S atoms on the hollow site is 2.43 Å, while that on the top site is 2.39 Å for MoS2. Similarly, For WS2 adsorption distance between the Li atom and the three affected S atoms on the hollow site is 2.43 Å, while that on the top site is 2.49 Å. To indicate comprehensively the thermodynamic properties of Li adsorption, at a high Li concentration; we calculate the Li adsorption energies on monolayer Mo1 ― 𝑥𝑊𝑥𝑆2 by the increasing Li concentration. For this purpose nine different intercalation states (Figure S2) from Li0.22MS2 to Li2MS2 where (M=Mo, W) with Li adsorption on both sides of the monolayer surface are constructed. On the surface of this monolayer, Li atoms are distributed uniformly on the favourable top sites for both sides of the Mo1 ― 𝑥𝑊𝑥𝑆2 layer. The Li adsorption energy decreases gradually (Figure 3) with the increasing Li content because of repulsive interactions between large number of Li atoms at high concentration and still Mo1 ― 𝑥𝑊𝑥𝑆2 monolayer can hold Li atoms in Li2Mo1 ― 𝑥𝑊𝑥𝑆2 with a high adsorption energy of 1.6 eV to1.4 eV (Table 2) which suggests that the Li2Mo1 ― 𝑥𝑊𝑥𝑆2 structures have high stability even at maximum Li content (Figure S3) which is better than graphite, the preferred anode material exhibiting an intercalation reaction with lithium to yield LiC6 corresponding to a theoretical capacity of 372 mAh g−1.85 These results are in good agreement with previous reported data.84,86 8 ACS Paragon Plus Environment

Page 8 of 34

Page 9 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


One of the major shortcomings in LIBs is Li dendrite formation from the anode which limit the operation and can cause the failure of Li-ion batteries.87 The problem arises due to weak adsorbate-adsorbent binding at high Li content which leads to the adsorbates clustering and decreases adsorbate capacity.88 In spite of the fact that 2D-materials provide more free surfaces for adsorption compared with bulk materials, thermal capacity of graphene anode has been demonstrated to be lower than that of graphite anode.89,90 The potential nucleation centres cause dendrite growth, which may turn into an issue with these types of anodes. Both experimental and theoretical studies of Li nucleation88,91 on graphene has been studied. To the best of our knowledge, Li nucleation on TMDs or any other non-graphene materials has not yet been studied so far. Hence prediction regarding Li nucleation at this stage cannot be over ruled. So to study the possibility of nucleation of Li on Mo1 ― 𝑥𝑊𝑥𝑆2 alloy, the cohesive energies of bulk Li has been calculated. Taking the value of bulk is a superior definition with regards to LIBs, as the formation of bulk Li89 represents anode failure and dendrite formation. With a specific goal to stay away from phase separation and formation of hazardous Li dendrites, the Li adsorption energy should be greater than the Li cohesive energy of bulk Li.88 The cohesive energy92 of a material with N atoms in a unit cell is defined as,

Ecoh 

 1    E x  E0  N atoms 

𝐸𝑥 is the total energy of the solid and 𝐸0 denotes the corresponding energy of the constituent atoms in bulk. As indicated by this definition, positive errors correspond to an over binding, where as negative errors correspond to under binding. The calculated bulk cohesive energies are 0.82, 0.80, 0.78 and 0.75 eV for Mo1 ― 𝑥𝑊𝑥𝑆2 alloys of x concentration 0, 0.33, 0.66 and 1 respectively which are very negligent in comparison to the adsorption energies of single lithium (1.74 eV to 1.44 eV) and adsorption energy at maximum Li concentrations (1.61 eV to 1.40 eV). This value suggests possibility of Li storage93 instead of forming Li nucleation which leads to the phase separation, aggregate into clusters and formation of macroscopic dendrites.



Figure 3: Variation of adsorption energies with increasing Li content on monolayer Mo1 ― 𝑥𝑊𝑥𝑆2 for different compositions of x.

Strain engineering is the most widely used and observable method to modulate the electronic structures of TMDs at a fundamental level.94 In TMDs, strain can be easily induced by many ways, which offers an intriguing opportunity to tune electronic properties of materials. Recently, Li et al.95,96 have shown that S-vacancies induced strain on basal plane of MoS2 surface optimizes catalytic activity of hydrogen evolution reaction which provides a new degree of freedom to employ the inherent catalytic activity of TMDs catalysts by strain. Here the quest is to find out and observe keenly the strain effect on adsorption energy. For this purpose, the adsorption energies of a single lithium atom as the function of the tensile strain ranging from 0% to 10% at an interval of 2% are calculated. Here, strain can be defined as 𝜀=

𝑎 - 𝑎0 𝑎0


Page 10 of 34

Page 11 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Here 𝑎0 and 𝑎 are the lattice constants of Mo1 ― 𝑥𝑊𝑥𝑆2 without strain and with different strains, respectively. The adsorption energy of strained materials is calculated by subtracting the total energy of lithiated Mo1 ― 𝑥𝑊𝑥𝑆2 with strain from the total energy of strained Mo1 ― 𝑥𝑊𝑥𝑆2 and total energy of isolated Li atom. Chen et al.86 studied Li adsorption on MoS2 as the function of the lattice constant ranging from 9.26 to 9.97 Å and found that adsorption energy decreases with both tensile and compressive strain and found maximum adsorption energy at 9.65 Å. External strain effects adsorption energy of alloy of MoS2 and MoSe2 ( MoS 2(1 x ) Se2 x alloy) having optimized lattice constant ‘a’ 3.198 Å and 3.328 Å respectively are studied and adsorption energy decreases quickly with elongating lattice constants.82 However, the present study which uses lattice constant of 3.16 Å97 for both MoS2 and WS2 with 0% lattice mismatch shows that (Figure 4a) the adsorption energy of Mo1 ― 𝑥𝑊𝑥𝑆2 alloy increases with increasing tensile strain (Table 2). These results are consistent with results of Hao et al..98 When the lattice constant elongates, the SMS bond angle (θS−Mo−S) increases and the inserted ions get larger space at the top site and less repulsion from the three neighbouring sulphur atoms which makes them more stable. Simultaneously the adsorption distance between lithium and Mo/W reduces greatly with increasing strain, which is in good agreement with the most universally accepted concepts of chemistry is that a shorter bond reflects a stronger bond: a correlation which relate bond shortening to bond strengthening.99,100 Figure 4(b) presents the calculated adsorption distance between lithium and Mo/W at different tensile strain.



Figure 4: (a) Variation of adsorption energies with increasing tensile strain on monolayer Mo1 ― 𝑥𝑊𝑥𝑆2 alloy for different compositions of x. (b) Effect of tensile strain on adsorption distance of Li from Mo and W in monolayer Mo1 ― 𝑥𝑊𝑥𝑆2.

3.2. Electronic Properties of Mo𝟏 ― 𝒙𝑾𝒙𝑺𝟐 sheet. TMD alloys have fascinated research enthusiasm due to its varied amalgamations of different 2D TMDs which could make them unique material having tunable electronic parameters/properties useful in various electronic applications. Such alloys can also be used as battery electrodes, and to have a better perception of the interaction of Li with the Mo1 ― 𝑥𝑊𝑥𝑆2 sheet, we calculated the electronic properties. To quantitatively calculate the amount of charge transfer from Li to Mo1 ― 𝑥𝑊𝑥𝑆2 sheet, Baders charge analysis has been performed. It shows that each Li atom donates a charge of 0.88-0.86 |e| to its adjacent S atoms which is compatible with the results of Ersan et. al.82 To get further information regarding the charge transfer and the bonding interaction of Li with the Mo1 ― 𝑥𝑊𝑥𝑆2 sheet, we calculated the corresponding charge density difference for Li inserted on monolayer Mo1 ― 𝑥𝑊𝑥𝑆2 (Figure 5) sheet. The charge density difference is defined by δρ = 𝜌Mo1 ― 𝑥𝑊𝑥𝑆2 ― Li ― 𝜌Mo1 ― 𝑥𝑊𝑥𝑆2 ― 𝜌Li where 𝜌Mo1 ― 𝑥𝑊𝑥𝑆2 ― Li, 𝜌Mo1 ― 𝑥𝑊𝑥𝑆2 and 𝜌Li are the charge densities of the system of Li adsorbed on Mo1 ― 𝑥𝑊𝑥𝑆2, pristine Mo1 ― 𝑥𝑊𝑥𝑆2 monolayer, and the isolated Li atom, respectively.


Page 12 of 34

Page 13 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5: Charge density difference distribution for Li atom adsorbed on monolayer Mo1 ― 𝑥𝑊𝑥𝑆2. The depletion and accumulation of charges, are indicated by Green and red colours respectively. (a) x=0, (b) x=0.33, (c) x=0.66, (d) x=1

From the analysis of charge density differences, there is a net loss of charge above the Li atom, which is accompanied by a net charge gain at the nearest S atoms, indicating a significant charge transfer between Li and S atoms. Metallic properties play an important role in the application of materials in LIBs. To examine the electronic properties, the DOS and band gaps of bare and Li-adsorbed Mo1 ― 𝑥𝑊𝑥𝑆2 sheets are calculated. PDOS analysis indicates that the DOS at the Fermi level are mostly dominated by d-orbital of both Mo and W atoms. We found that, after lithiation, the conduction band minimum of the Mo1 ― 𝑥𝑊𝑥𝑆2 sheet moves towards to the Fermi level, indicating formation of metallic structure. The PDOS and total DOS for all the bare and lithiated systems are shown in Figure 6.




Page 14 of 34

Page 15 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 6: Projected Density of States plot for bare and lithiated surface of monolayer Mo1 ― 𝑥𝑊𝑥𝑆2 including majority orbital contribution. (a) x=0, (b) x=0.33, (c) x=0.66, (d) x=1. The Fermi level is set to be zero.

The calculated band gap for MoS2 is ~1.86 eV and for WS2 it is ~1.99 eV, which is consistent with previous results.101,102 Band gap calculation (Table 1) shows that all bare Mo1 ― 𝑥 𝑊𝑥𝑆2 sheets are semiconducting in nature with a band gap of 1.86 eV-1.99 eV. As concentration of x increases, the value of band gap first decreases and then increases up to band gap value of WS2. This can be explained as, both Mo and W d-orbitals have different contributions to conduction bands of MoS2 and WS2 but almost identical contributions to valence bands.103 The HOMO for both MoS2 and WS2 is contributed by d xy and d x 2  y 2 orbital’s whereas the LUMO of MoS2 is contributed by d z 2 orbital only and for WS2 it is d xy , d x 2  y 2 and d z 2 orbitals.104 Because of common type of orbital contributions, W atoms directly interact in the formation of HOMO of 15 ACS Paragon Plus Environment


Page 16 of 34

Mo1 ― 𝑥𝑊𝑥𝑆2 alloy and results a linear up shift of the HOMO energy level with W composition. However, Because of different orbital compositions in the LUMO and higher LUMO energy of WS2, the energy of the W atom is not sufficient for raising the energy level and then LUMO bowing31 occurred rather than a linear increase. However in case of chalcogenide alloys of MoS 2 (1 x ) Se2 x , increase in selenide concentration leads to decrease in band gap.82 This is because

when metal-chalcogen bond length increases, the overlapping between metal d-orbital and chalcogen p-orbital decreases and magnitude of band gap decreases.103 Table 1. Calculated Band gap before Lithium intercalation and quantity of charge transferred after Lithium intercalation. Concentration x

Band gap of Bare sheets(eV)

Charge transfer (|e|)

0.00

1.86

0.88

0.33

1.84

0.87

0.66

1.91

0.87

1.00

1.99

0.86

3.3. Li Diffusion on surface of Mo𝟏 ― 𝒙𝑾𝒙𝑺𝟐 sheet. The power capability of LIBs depends critically on the speed at which Li+ ions migrate through the electrolyte and electrode. Therefore, a promising strategy is to create high-power LIBs to develop new materials with high electrical conductivity for fast electron transfer with short diffusion distances for fast lithium ion diffusion which depends on the mobility of the intercalating ion. So to find out the motion of lithium atom on the Mo1 ― 𝑥𝑊𝑥𝑆2 monolayer, we consequently identify its minimum energy paths (MEP) and calculate the corresponding diffusion barriers using the climbing image nudged elastic band (CINEB) method. Because of the structural reason, we choose two nearest neighbouring molybdenum atoms, the typical migration path of an intercalated ion is from one top site to another adjacent top site through a hollow intermediate site (Figure 7). Before the CI-NEB calculation, initial and final images of the structures are fully relaxed and a number of


Page 17 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7: Schematic representation of Li diffusion path on Mo1 - xWxS2 alloy of x=0.33 from one top position to another through hollow site. (a) Bare surface (b) Lithiated surface. The blue, green, yellow and maroon balls denote Mo, W, S and Li atoms respectively.

intermediate images were inserted between the initial and final states along the reaction coordinate as shown in Figure 7. The diffusion pathway for MoS2 and WS2, is characterized by the two symmetrical maxima and a local minimum. But in case of alloys we found two antisymmetric maxima. The migration barrier on the surface of MoS2 is 0.202 eV and it is 0.183 eV for WS2 well agreed with previous results,20,105,106 which implies that the monolayer Mo1 ― 𝑥𝑊𝑥𝑆2 could exhibit fast charge discharge capability for Li. But in case of alloys of x=0.33, when Li migrates from TW site to TMo site, the maximum at TMo site is slightly higher (0.002 eV) than the TW site. Similarly at x=0.66, when Li migrates from TMo site to TW site, the maximum at TW site is slightly (0.004 eV) lower than TMo site. An optimal path of lithium diffusion for all the alloys is from one top site to the nearest neighbouring top site passing through a hollow site, is shown in figure 8.



Figure 8: Energy profiles for Lithium Diffusion on monolayer Mo1 ― 𝑥𝑊𝑥𝑆2. Blue line indicates bare surface and red line indicate lithiated surface.

Moreover, to restrain the influence of concentration of inserted ions on the energy barriers, barrier energy at Li2Mo𝑥𝑊1 ― 𝑥𝑆2 are calculated. A lithium atom was detached from the case of nine lithium atoms adsorbed at one part of surface (i.e. maximum of lithium concentration for one-sided lithium covered surface) namely, the diffusion path for eight lithium atoms adsorbed on the MoS2 monolayer are studied in detail. The barrier energy follows the same trend as in the case of Li0.22 Mo1 xWx S 2 . On the surface of Li2MS2 (M=Mo/W), the activation energy varies between 0.315 eV to 0.173 eV (Table 2) which is comparable with that of a single lithium atom adsorbed on the Mo1 ― 𝑥𝑊𝑥𝑆2 monolayer (0.202-0.183 eV) indicating that the lithium concentration has a weaker effect on the diffusion of lithium atom. These results are in good agreement with Chen et al.86 result. However, the energy profile is affected by the concentration of more Li atoms. For a single lithium migration in bare surface, when lithium 18 ACS Paragon Plus Environment

Page 18 of 34

Page 19 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


migrates from one top site to another through hollow site, we found one local minimum at the hollow site and two maxima in between hollow and top sites. However, in a lithium covered surface, we found only one maximum at hollow site because of repulsion with other lithium atoms as shown in figure 8. In order to investigate whether Mo1 ― 𝑥𝑊𝑥𝑆2 alloy is suitable for flexible electronic devices, it is necessary to study the effect of strain on barrier energy. To quantify this, we calculated the Li diffusion barriers on Mo1 ― 𝑥𝑊𝑥𝑆2 alloy with a 6% of tensile strain. Here to precisely determine the minimum energy path (MEP) together with the diffusion barriers, 6% of tensile strain is taken because, it has been proven that 6% tensile strain can be readily achievable by experiments and the strength of individual TMDs monolayer’s are most stable at 6% tensile strain.107,108 We find that barrier energy remains unaffected by application of strain (Table 2). 3.4. Theoretical open-circuit voltage and Specific Capacity. The calculated theoretical opencircuit voltage (OCV) for Li z MS 2 (where M=Mo/W and z is no Li atoms adsorbed) well indicate the performances of material in LIBs. We estimated the open-circuit voltage (OCV) for Li adsorption as the change of Gibbs free energy divided by the number of transferred Li ions. It is noteworthy that the volume and entropy effects are customarily negligible during the reaction.109 Since the changes in entropy and volume are assumed to be zero, the free energy (ΔG) can be estimated by the formula, ΔG = ΔE+PΔV−TΔS, where the change in Gibbs free energy is dominated by the formation energy, ΔE, obtained from our calculations. The formation energy is defined as the energy difference before and after the intercalation of Li on Mo1 ― 𝑥𝑊𝑥𝑆2 sheet. The electrochemical reaction taking place is as following:

MS 2  zLi   ne   Li z MS 2 Where M is Mo/W and z is the number of Li+ ions transferred The Theoretical open-circuit voltage is calculated by



Vavg 

E Liz1MS2  E Liz2 MS2  ( z 2  z1 ) E Li ( z 2  z1 )

where E Liz1MS2 , E Liz2 MS2 , and ELi are the total energies of the system of MS2 with z1 and z2 Li adsorbed, and Energy of a Li atom in bulk body-centered cubic (bcc) structure respectively. For Li intercalation on the Mo1 ― 𝑥𝑊𝑥𝑆2 monolayer, lithium atoms are adsorbed at the top sites, which are the most stable sites for Li adsorption. As like MoS2 monolayer Mo1 ― 𝑥𝑊𝑥𝑆2 monolayer can also store Li atoms up to Li2Mo1 ― 𝑥𝑊𝑥𝑆2, (maximum lithium storage) with a high binding energy of 1.61 eV to 1.42 eV. We established a positive average open-circuit voltage which suggests that Li atoms can efficiently be absorbed onto the monolayer Mo1 ― 𝑥𝑊𝑥𝑆2 sheet. Open-circuit voltage for different Li intercalation stages with 6, 12 and 18 no of lithium atoms (x = 0.67, 1.33, and 2) are calculated. The OCV drops from 0.81 to 0.68 V for MoS2 and 0.68 to 0.61 V for WS2 (Table S3). This is between those of reported anode materials 0.11 V for graphite and 1.5-1.8 V for TiO2,110–112 On the basis of the above analyses, we accomplished that Mo1 ― 𝑥𝑊𝑥𝑆2 monolayer could be a potential anode for the application of an electrode material in LIBs. To further study the electrochemical properties of monolayer Mo1 ― 𝑥𝑊𝑥𝑆2 alloys as a anode materials, the theoretical specific capacity has been calculated, which could well imply the performances of the anode in LIBs. The specific capacity of anode material is proportional to the number of adsorbed atoms and has been calculated at maximum concentration of adsorbed atoms. The average theoretical capacity109 is estimated using the given equation, Q

nF W

In the above equation, n represents the maximum number of Li atoms adsorbed per formula unit of Mo1 ― 𝑥𝑊𝑥𝑆2 alloy (in this case, n = 2). F is the Faradays constant (26,800 mA h/mol), and M is the molecular mass of per unit cell of Mo1 ― 𝑥𝑊𝑥𝑆2. The maximum adsorption concentration corresponds to Li2 M 1 xWx S 2 and represents the highest Li storage capacity, which leads a


Page 20 of 34

Page 21 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


theoretical storage capacity of 335 mAh/g for MoS2 and 216 mAh/g for WS2 well agreed with previous results.59 The theoretical specific capacity of other alloys is shown in table S3. At maximum Li concentration, minute structural deviations have been observed. The lattice constant of MoS2 expands from 3.16 to 3.27 Å i.e. increases by 3.5 %, and for WS2 it expands from 3.16 to 3.33 Å (increases by 5.33 %) This is a result of greater size of W atoms than Mo atoms and furthermore, for other different alloys it stays in the middle of the two. The lattice constant enlarges to 3.94 % in case of x=0.33 and 4.74 % in case of x=0.66 of Mo1 ― xWxS2 alloys. Hence it can be concluded that, lithiation does not have any significant effect towards the structural distortion of system parameters. From the above all analysis, we found that MoS2 has higher adsorption energy than WS2, where as WS2 has a lower diffusion barrier than MoS2. The adsorption energy versus diffusion barrier plots is shown in figure 9. Table 2. Lithium Adsorption Energy (eV) and Lithium Diffusion Barrier energy (eV) for different alloys. Effect of strain and Concentration on both Adsorption energy and Diffusion Barrier. Lithium Adsorption Energy ( eV)

Lithium Diffusion Barrier (eV)

Concentration

Observed

Effect of

Effect of

Observed

Effect of

Effect of

x

value

concentration

strain

value

concentration

strain (6 %)

(10%) 0.00

1.74

1.61

2.79

0.202

0.315

0.199

0.33

1.63

1.54

2.66

0.200

0.280

0.198

0.66

1.52

1.48

2.54

0.189

0.220

0.188

1.00

1.44

1.42

2.44

0.183

0.172

0.178



Figure 9: Li adsorption energies and diffusion barriers on monolayer Mo1-xWxS2 compared with different compositions of x. (a) migration of Li on bare surface and (b) migration of Li on lithiated surface.

Conclusions In summary, by employing periodic density functional theory calculations, we systematically investigated the adsorption and diffusion of Li atom on monolayer Mo1 ― 𝑥𝑊𝑥𝑆2 alloy. We observed that the lowest energy adsorption positions of Li are at the top site of monolayer alloy rather than the hollow site with adsorption energy of 1.78 to 1.48 eV. To get better perception of interaction between Li and Mo1 ― 𝑥𝑊𝑥𝑆2 alloy, electronic analysis has been performed. The diffusion of Li on the surface of monolayer Mo1 ― 𝑥𝑊𝑥𝑆2 alloy was calculated and a low diffusion barrier of 0.202 to 0.183 eV was observed when Li atom migrates on the surface of alloy. When the surface is covered by Li, the barrier energy varies between 0.305 eV to 0.172 eV. So the Li ions have low energy barriers for the migration in Mo1 ― 𝑥𝑊𝑥𝑆2, which is advantageous for the rate performance of batteries. We find negligible average open-circuit voltage and high specific capacity for all the systems. The effect of tensile strain exceptionally affects the lithium adsorption energy. With increasing tensile strain from 0% to 10% with intervals of 2%, the adsorption energy increases very quickly, where as adsorption distance of lithium from Mo/W decreases. Concentration of more lithium atom induces repulsive interactions and decreases adsorption energy. However, the barrier energy is affected only by concentration and remains unaffected by strain.


Page 22 of 34

Page 23 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


MoS2 has comparatively higher adsorption energy than WS2, conversely WS2 has a lower diffusion barrier than MoS2. So by taking into account the interdependent electrochemical performance, worthiness of different TMDs could be successfully achieved by alloying these two materials. Consequently, MoS2−WS2 alloy is a promising material for LIBs. Supporting Information Li adsorption at different sites, Optimized bond distances and bond angles before and after lithium adsorption. Optimized geometry of nine different intercalation states of MoS2 is shown. Top and side view of monolayer LiMo1 ― 𝑥𝑊𝑥𝑆2 at maximum lithium concentration. Effect of tensile strain on adsorption energy and adsorption distance between Li and Mo/W of monolayer Mo1 ― 𝑥𝑊𝑥𝑆2 sheets are given. Calculated adsorption energies of lithium on monolayer Mo1 ― 𝑥𝑊𝑥𝑆2, at different positions, Band gap before Li adsorption, charge transfer value for lithium adsorption, Open Circuit Voltage and Specific Capacity has been provided in the supporting information. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] Present address: 2Department

of Chemical Sciences, Indian Institute of Science Education and Research Kolkata,

Mohanpur Nadia 741 246, West Bengal, India Notes The authors declare no competing financial interest.

Acknowledgements S.P. acknowledges the J.C. Bose Fellowship grant of DST. G.B. acknowledges Council of Scientific and Industrial Research for providing Junior Research fellowship. 23 ACS Paragon Plus Environment


References: (1)

Tarascon, J.-M.; Armand, M. Issues and Challenges Facing Rechargeable Lithium Batteries. Nature 2001, 414, 359.

(2)

Kang, B.; Ceder, G. Battery Materials for Ultrafast Charging and Discharging. Nature 2009, 458, 190.

(3)

Meini, S.; Elazari, R.; Rosenman, A.; Garsuch, A.; Aurbach, D. The Use of Redox Mediators for Enhancing Utilization of Li2S Cathodes for Advanced Li–S Battery Systems. J. Phys. Chem. Lett. 2014, 5, 915–918.

(4)

Song, K.; Seo, D.-H.; Jo, M. R.; Kim, Y.-I.; Kang, K.; Kang, Y.-M. Tailored Oxygen Framework of Li4Ti5O12 Nanorods for High-Power Li Ion Battery. J. Phys. Chem. Lett. 2014, 5, 1368–1373.

(5)

Aricò, A. S.; Bruce, P.; Scrosati, B.; Tarascon, J.-M.; van Schalkwijk, W. Nanostructured Materials for Advanced Energy Conversion and Storage Devices. Nat. Mater. 2005, 4, 366.

(6)

Liu, C.; Li, F.; Ma, L.-P.; Cheng, H.-M. Advanced Materials for Energy Storage. Adv. Mater. 2010, 22, E28–E62.

(7)

Korgel, B. A. Nanomaterials Developments for Higher-Performance Lithium Ion Batteries. J. Phys. Chem. Lett. 2014, 5, 749–750.

(8)

Manthiram, A. Materials Challenges and Opportunities of Lithium Ion Batteries. J. Phys. Chem. Lett. 2011, 2, 176–184.

(9)

Wang, G.; Shen, X.; Yao, J.; Park, J. Graphene Nanosheets for Enhanced Lithium Storage in Lithium Ion Batteries. Carbon N. Y. 2009, 47, 2049–2053.

(10)

Yoo, E.; Kim, J.; Hosono, E.; Zhou, H.; Kudo, T.; Honma, I. Large Reversible Li Storage of Graphene Nanosheet Families for Use in Rechargeable Lithium Ion Batteries. Nano Lett. 2008, 8, 2277–2282.

(11)

Chhowalla, M.; Shin, H. S.; Eda, G.; Li, L.-J.; Loh, K. P.; Zhang, H. The Chemistry of Two-Dimensional Layered Transition Metal Dichalcogenide Nanosheets. Nat. Chem. 2013, 5, 263.

(12)

Huang, X.; Zeng, Z.; Zhang, H. Metal Dichalcogenide Nanosheets: Preparation, Properties and Applications. Chem. Soc. Rev. 2013, 42, 1934–1946.

(13)

Lv, R.; Robinson, J. A.; Schaak, R. E.; Sun, D.; Sun, Y.; Mallouk, T. E.; Terrones, M. 24 ACS Paragon Plus Environment

Page 24 of 34

Page 25 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Transition Metal Dichalcogenides and Beyond: Synthesis, Properties, and Applications of Single- and Few-Layer Nanosheets. Acc. Chem. Res. 2015, 48, 56–64. (14)

Tan, C.; Zhang, H. Two-Dimensional Transition Metal Dichalcogenide Nanosheet-Based Composites. Chem. Soc. Rev. 2015, 44, 2713–2731.

(15)

Rasmussen, F. A.; Thygesen, K. S. Computational 2D Materials Database: Electronic Structure of Transition-Metal Dichalcogenides and Oxides. J. Phys. Chem. C 2015, 119, 13169–13183.

(16)

Tan, C.; Cao, X.; Wu, X.-J.; He, Q.; Yang, J.; Zhang, X.; Chen, J.; Zhao, W.; Han, S.; Nam, G.-H.; et al. Recent Advances in Ultrathin Two-Dimensional Nanomaterials. Chem. Rev. 2017, 117, 6225–6331.

(17)

Wang, Q. H.; Kalantar-Zadeh, K.; Kis, A.; Coleman, J. N.; Strano, M. S. Electronics and Optoelectronics of Two-Dimensional Transition Metal Dichalcogenides. Nat. Nanotechnol. 2012, 7, 699.

(18)

Lai, X.; Halpert, J. E.; Wang, D. Recent Advances in Micro-/Nano-Structured Hollow Spheres for Energy Applications: From Simple to Complex Systems. Energy Environ. Sci. 2012, 5, 5604–5618.

(19)

Yu, X.-Y.; Yu, L.; Lou, X. W. (David). Metal Sulfide Hollow Nanostructures for Electrochemical Energy Storage. Adv. Energy Mater. 2015, 6, 1501333.

(20)

Mak, K. F.; Lee, C.; Hone, J.; Shan, J.; Heinz, T. F. Atomically Thin MoS2: A New Direct-Gap Semiconductor. Phys. Rev. Lett. 2010, 105, 136805.

(21)

Lee, Y.-H.; Zhang, X.-Q.; Zhang, W.; Chang, M.-T.; Lin, C.-T.; Chang, K.-D.; Yu, Y.-C.; Wang, J. T.-W.; Chang, C.-S.; Li, L.-J.; et al. Synthesis of Large-Area MoS2 Atomic Layers with Chemical Vapor Deposition. Adv. Mater. 2012, 24, 2320–2325.

(22)

Lauritsen, J. V; Kibsgaard, J.; Helveg, S.; Topsøe, H.; Clausen, B. S.; Lægsgaard, E.; Besenbacher, F. Size-Dependent Structure of MoS2 Nanocrystals. Nat. Nanotechnol. 2007, 2, 53.

(23)

Remìkar, M.; Škraba, Z.; Regula, M.; Ballif, C.; Sanjinés, R.; Lévy, F. New Crystal Structures of WS2: Microtubes, Ribbons, and Ropes. Adv. Mater. 1999, 10, 246–249.

(24)

Schutte, W. J.; De Boer, J. L.; Jellinek, F. Crystal Structures of Tungsten Disulfide and Diselenide. J. Solid State Chem. 1987, 70, 207–209.

(25)

Tenne, R.; Margulis, L.; Genut, M.; Hodes, G. Polyhedral and Cylindrical Structures of 25 ACS Paragon Plus Environment


Tungsten Disulphide. Nature 1992, 360, 444. (26)

Choe, D.-H.; Sung, H.-J.; Chang, K. J. Understanding Topological Phase Transition in Monolayer Transition Metal Dichalcogenides. Phys. Rev. B 2016, 93, 125109.

(27)

Liu, J.; Wang, H.; Fang, C.; Fu, L.; Qian, X. Van Der Waals Stacking-Induced Topological Phase Transition in Layered Ternary Transition Metal Chalcogenides. Nano Lett. 2017, 17, 467–475.

(28)

Li, Y.; Wu, D.; Zhou, Z.; Cabrera, C. R.; Chen, Z. Enhanced Li Adsorption and Diffusion on MoS2 Zigzag Nanoribbons by Edge Effects: A Computational Study. J. Phys. Chem. Lett. 2012, 3, 2221–2227.

(29)

Hinnemann, B.; Moses, P. G.; Bonde, J.; Jørgensen, K. P.; Nielsen, J. H.; Horch, S.; Chorkendorff, I.; Nørskov, J. K. Biomimetic Hydrogen Evolution: MoS2 Nanoparticles as Catalyst for Hydrogen Evolution. J. Am. Chem. Soc. 2005, 127, 5308–5309.

(30)

Pandey, M.; Jacobsen, K. W.; Thygesen, K. S. Atomically Thin Ordered Alloys of Transition Metal Dichalcogenides: Stability and Band Structures. J. Phys. Chem. C 2016, 120, 23024–23029.

(31)

Chen, Y.; Xi, J.; Dumcenco, D. O.; Liu, Z.; Suenaga, K.; Wang, D.; Shuai, Z.; Huang, Y.S.; Xie, L. Tunable Band Gap Photoluminescence from Atomically Thin Transition-Metal Dichalcogenide Alloys. ACS Nano 2013, 7, 4610–4616.

(32)

Lin, Y.-C.; Dumcenco, D. O.; Komsa, H.-P.; Niimi, Y.; Krasheninnikov, A. V; Huang, Y.S.; Suenaga, K. Properties of Individual Dopant Atoms in Single-Layer MoS2: Atomic Structure, Migration, and Enhanced Reactivity. Adv. Mater. 2014, 26, 2857–2861.

(33)

Xie, L. M. Two-Dimensional Transition Metal Dichalcogenide Alloys: Preparation, Characterization and Applications. Nanoscale 2015, 7, 18392–18401.

(34)

Srivastava, S. K.; Mandal, T. K.; Samantaray, B. K. Studies on Layer Disorder, Microstructural Parameters and Other Properties of Tungsten-Substitued Molybdenum Disulfide, Mo1-xWxS2 (0≤ x ≤1). Synth. Met. 1997, 90, 135–142.

(35)

Nath, M.; Mukhopadhyay, K.; Rao, C. N. R. Mo1-xWxS2 Nanotubes and Related Structures. Chem. Phys. Lett. 2002, 352, 163–168.

(36)

Dumcenco, D. O.; Chen, K. Y.; Wang, Y. P.; Huang, Y. S.; Tiong, K. K. Raman Study of 2H-Mo1-xWxS2 Layered Mixed Crystals. J. Alloys Compd. 2010, 506, 940–943.

(37)

He, Q.; Wan, Y.; Jiang, H.; Wu, C.; Sun, Z.; Chen, S.; Zhou, Y.; Chen, H.; Liu, D.; 26 ACS Paragon Plus Environment

Page 26 of 34

Page 27 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Haleem, Y. A.; et al. High-Metallic-Phase-Concentration Mo1-xW2S2 Nanosheets with Expanded Interlayers as Efficient Electrocatalysts. Nano Res. 2018, 11, 1687–1698. (38)

Liu, H.; Antwi, K. K. A.; Chua, S.; Chi, D. Vapor-Phase Growth and Characterization of Mo(1-x)W(x)S2 (0  x  1) Atomic Layers on 2-Inch Sapphire Substrates. Nanoscale 2014, 6, 624–629.

(39)

Komsa, H.-P.; Krasheninnikov, A. V. Two-Dimensional Transition Metal Dichalcogenide Alloys: Stability and Electronic Properties. J. Phys. Chem. Lett. 2012, 3, 3652–3656.

(40)

Song, J.-G.; Ryu, G. H.; Lee, S. J.; Sim, S.; Lee, C. W.; Choi, T.; Jung, H.; Kim, Y.; Lee, Z.; Myoung, J.-M.; et al. Controllable Synthesis of Molybdenum Tungsten Disulfide Alloy for Vertically Composition-Controlled Multilayer. Nat. Commun. 2015, 6, 7817.

(41)

Dumcenco, D. O.; Kobayashi, H.; Liu, Z.; Huang, Y.-S.; Suenaga, K. Visualization and Quantification of Transition Metal Atomic Mixing in Mo1-xWxS2 Single Layers. Nat. Commun. 2013, 4, 1351.

(42)

Wang, Z.; Shen, Y.; Ito, Y.; Zhang, Y.; Du, J.; Fujita, T.; Hirata, A.; Tang, Z.; Chen, M. Synthesizing 1T–1H Two-Phase Mo1-xWxS2 Monolayers by Chemical Vapor Deposition. ACS Nano 2018, 12, 1571–1579.

(43)

Kappera, R.; Voiry, D.; Yalcin, S. E.; Branch, B.; Gupta, G.; Mohite, A. D.; Chhowalla, M. Phase-Engineered Low-Resistance Contacts for Ultrathin MoS2 Transistors. Nat. Mater. 2014, 13, 1128.

(44)

Zhu, J.; Wang, Z.; Yu, H.; Li, N.; Zhang, J.; Meng, J.; Liao, M.; Zhao, J.; Lu, X.; Du, L.; et al. Argon Plasma Induced Phase Transition in Monolayer MoS2. J. Am. Chem. Soc. 2017, 139, 10216–10219.

(45)

Enyashin, A. N.; Yadgarov, L.; Houben, L.; Popov, I.; Weidenbach, M.; Tenne, R.; BarSadan, M.; Seifert, G. New Route for Stabilization of 1T-WS2 and MoS2 Phases. J. Phys. Chem. C 2011, 115, 24586–24591.

(46)

Wang, L.; Xu, Z.; Wang, W.; Bai, X. Atomic Mechanism of Dynamic Electrochemical Lithiation Processes of MoS2 Nanosheets. J. Am. Chem. Soc. 2014, 136, 6693–6697.

(47)

Song, S.; Keum, D. H.; Cho, S.; Perello, D.; Kim, Y.; Lee, Y. H. Room Temperature Semiconductor–Metal Transition of MoTe2 Thin Films Engineered by Strain. Nano Lett. 2016, 16, 188–193.

(48)

Kretschmer, S.; Komsa, H.-P.; Bøggild, P.; Krasheninnikov, A. V. Structural 27 ACS Paragon Plus Environment


Transformations in Two-Dimensional Transition-Metal Dichalcogenide MoS2 under an Electron Beam: Insights from First-Principles Calculations. J. Phys. Chem. Lett. 2017, 8, 3061–3067. (49)

Haering, R. R.; Stiles, J. A. R.; Brandt, K. Lithium Molybdenum Disulphide Battery Cathode. US Pat. 1980, 4224390.

(50)

Hwang, H.; Kim, H.; Cho, J. MoS2 Nanoplates Consisting of Disordered Graphene-like Layers for High Rate Lithium Battery Anode Materials. Nano Lett. 2011, 11, 4826–4830.

(51)

Ding, S.; Zhang, D.; Chen, J. S.; Lou, X. W. (David). Facile Synthesis of Hierarchical MoS2 Microspheres Composed of Few-Layered Nanosheets and Their Lithium Storage Properties. Nanoscale 2012, 4, 95–98.

(52)

Du, G.; Guo, Z.; Wang, S.; Zeng, R.; Chen, Z.; Liu, H. Superior Stability and High Capacity of Restacked Molybdenum Disulfide as Anode Material for Lithium Ion Batteries. Chem. Commun. 2010, 46, 1106–1108.

(53)

Stephenson, T.; Li, Z.; Olsen, B.; Mitlin, D. Lithium Ion Battery Applications of Molybdenum Disulfide (MoS2) Nanocomposites. Energy Environ. Sci. 2014, 7, 209–231.

(54)

Jing, Y.; Zhou, Z.; Cabrera, C. R.; Chen, Z. Metallic VS2 Monolayer: A Promising 2D Anode Material for Lithium Ion Batteries. J. Phys. Chem. C 2013, 117, 25409–25413.

(55)

Wang, D.; Liu, Y.; Meng, X.; Wei, Y.; Zhao, Y.; Pang, Q.; Chen, G. Two-Dimensional VS2 Monolayers as Potential Anode Materials for Lithium-Ion Batteries and beyond: First-Principles Calculations. J. Mater. Chem. A 2017, 5, 21370–21377.

(56)

Bhandavat, R.; David, L.; Singh, G. Synthesis of Surface-Functionalized WS2 Nanosheets and Performance as Li-Ion Battery Anodes. J. Phys. Chem. Lett. 2012, 3, 1523–1530.

(57)

Zhai, C.; Du, N.; Yang, H. Z. D. Large-Scale Synthesis of Ultrathin Hexagonal Tin Disulfide Nanosheets with Highly Reversible Lithium Storage. Chem. Commun. 2011, 47, 1270–1272.

(58)

Karmakar, S.; Chowdhury, C.; Datta, A. Two-Dimensional Group IV Monochalcogenides: Anode Materials for Li-Ion Batteries. J. Phys. Chem. C 2016, 120, 14522–14530.

(59)

Deng, S.; Wang, L.; Hou, T.; Li, Y. Two-Dimensional MnO2 as a Better Cathode Material for Lithium Ion Batteries. J. Phys. Chem. C 2015, 119, 28783–28788.

(60)

Chowdhury, C.; Datta, A. Exotic Physics and Chemistry of Two-Dimensional 28 ACS Paragon Plus Environment

Page 28 of 34

Page 29 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Phosphorus: Phosphorene. J. Phys. Chem. Lett. 2017, 8, 2909–2916. (61)

Li, H.; Li, W.; Ma, L.; Chen, W.; Wang, J. Electrochemical Lithiation/Delithiation Performances of 3D Flowerlike MoS2 Powders Prepared by Ionic Liquid Assisted Hydrothermal Route. J. Alloys Compd. 2009, 471, 442–447.

(62)

Wang, S.; Guan, B. Y.; Yu, L.; Lou, X. W. (David). Rational Design of Three-Layered TiO2@Carbon@MoS2 Hierarchical Nanotubes for Enhanced Lithium Storage. Adv. Mater. 2017, 29, 1702724.

(63)

Sun, Q.; Dai, Y.; Ma, Y.; Jing, T.; Wei, W.; Huang, B. Ab Initio Prediction and Characterization of Mo2C Monolayer as Anodes for Lithium-Ion and Sodium-Ion Batteries. J. Phys. Chem. Lett. 2016, 7, 937–943.

(64)

Zhang, L.; Sun, D.; Kang, J.; Feng, J.; Bechtel, H. A.; Wang, L.-W.; Cairns, E. J.; Guo, J. Electrochemical Reaction Mechanism of the MoS2 Electrode in a Lithium-Ion Cell Revealed by in Situ and Operando X-Ray Absorption Spectroscopy. Nano Lett. 2018, 18, 1466–1475.

(65)

Morant-Giner, M.; Sanchis-Gual, R.; Romero, J.; Alberola, A.; García-Cruz, L.; Agouram, S.; Galbiati, M.; Padial, N. M.; Waerenborgh, J. C.; Martí-Gastaldo, C.; et al. Prussian Blue@MoS2 Layer Composites as Highly Efficient Cathodes for Sodium- and PotassiumIon Batteries. Adv. Funct. Mater. 2017, 28, 1706125.

(66)

Radisavljevic, B.; Whitwick, M. B.; Kis, A. Integrated Circuits and Logic Operations Based on Single-Layer MoS2. ACS Nano 2011, 5, 9934–9938.

(67)

Giannozzi, P.; Baroni, S.; Bonini, N.; Calandra, M.; Car, R.; Cavazzoni, C.; Ceresoli, D.; Chiarotti, G. L.; Cococcioni, M.; Dabo, I.; et al. QUANTUM ESPRESSO: A Modular and Open-Source Software Project for Quantum Simulations of Materials. J. Phys. Condens. Matter 2009, 21, 395502.

(68)

Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865–3868.

(69)

Grimme, S. Semiempirical GGA-Type Density Functional Constructed with a LongRange Dispersion Correction. J. Comput. Chem. 2006, 27, 1787–1799.

(70)

Monkhorst, H. J.; Pack, J. D. Special Points for Brillouin-Zone Integrations. Phys. Rev. B 1976, 13, 5188–5192.

(71)

Henkelman, W. T. and E. S. and G. A Grid-Based Bader Analysis Algorithm without 29 ACS Paragon Plus Environment


Lattice Bias. J. Phys. Condens. Matter 2009, 21, 84204. (72)

Henkelman, G.; Uberuaga, B. P.; Jónsson, H. A Climbing Image Nudged Elastic Band Method for Finding Saddle Points and Minimum Energy Paths. J. Chem. Phys. 2000, 113, 9901–9904.

(73)

Zhang, X.; Lai, Z.; Tan, C.; Zhang, H. Solution-Processed Two-Dimensional MoS2 Nanosheets: Preparation, Hybridization, and Applications. Angew. Chem. Int. Ed. Engl. 2016, 55, 8816–8838.

(74)

Wang, H.; Lu, Z.; Xu, S.; Kong, D.; Cha, J. J.; Zheng, G.; Hsu, P.-C.; Yan, K.; Bradshaw, D.; Prinz, F. B.; et al. Electrochemical Tuning of Vertically Aligned MoS2 Nanofilms and Its Application in Improving Hydrogen Evolution Reaction. Proc. Natl. Acad. Sci. U. S. A. 2013, 110, 19701–19706.

(75)

Wang, T.; Chen, S.; Pang, H.; Xue, H.; Yu, Y. MoS2‐Based Nanocomposites for Electrochemical Energy Storage. Adv. Sci. 2017, 4, 1600289.

(76)

Wilson, J. A.; Yoffe, A. D. The Transition Metal Dichalcogenides Discussion and Interpretation of the Observed Optical, Electrical and Structural Properties. Adv. Phys. 1969, 18, 193–335.

(77)

Lin, Y.-C.; Dumcenco, D. O.; Huang, Y.-S.; Suenaga, K. Atomic Mechanism of the Semiconducting-to-Metallic Phase Transition in Single-Layered MoS2. Nat. Nanotechnol. 2014, 9, 391.

(78)

Nasr Esfahani, D.; Leenaerts, O.; Sahin, H.; Partoens, B.; Peeters, F. M. Structural Transitions in Monolayer MoS2 by Lithium Adsorption. J. Phys. Chem. C 2015, 119, 10602–10609.

(79)

Pandey, M.; Bothra, P.; Pati, S. K. Phase Transition of MoS2 Bilayer Structures. J. Phys. Chem. C 2016, 120, 3776–3780.

(80)

Fan, S.; Zou, X.; Du, H.; Gan, L.; Xu, C.; Lv, W.; He, Y.-B.; Yang, Q.-H.; Kang, F.; Li, J. Theoretical Investigation of the Intercalation Chemistry of Lithium/Sodium Ions in Transition Metal Dichalcogenides. J. Phys. Chem. C 2017, 121, 13599–13605.

(81)

Kan, M.; Wang, J. Y.; Li, X. W.; Zhang, S. H.; Li, Y. W.; Kawazoe, Y.; Sun, Q.; Jena, P. Structures and Phase Transition of a MoS2 Monolayer. J. Phys. Chem. C 2014, 118, 1515– 1522.

(82)

Ersan, F.; Gökoğlu, G.; Aktürk, E. Adsorption and Diffusion of Lithium on Monolayer 30 ACS Paragon Plus Environment

Page 30 of 34

Page 31 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Transition Metal Dichalcogenides (MoS2(1-x)Se2x) Alloys. J. Phys. Chem. C 2015, 119, 28648–28653. (83)

Andersen, A.; Kathmann, S. M.; Lilga, M. A.; Albrecht, K. O.; Hallen, R. T.; Mei, D. First-Principles Characterization of Potassium Intercalation in Hexagonal 2H-MoS2. J. Phys. Chem. C 2012, 116, 1826–1832.

(84)

Ersan, F.; Ozaydin, H. D.; Gökoğlu, G.; Aktürk, E. Theoretical Investigation of Lithium Adsorption, Diffusion and Coverage on MX2 (M=Mo, W; X=O, S, Se, Te) Monolayers. Appl. Surf. Sci. 2017, 425, 301–306.

(85)

Nagaura, T.; Tozawa, K. Lithium Ion Rechargeable Battery. Prog. Batter. Sol. Cells 1990, 9, 209–217.

(86)

Chen, H. J. ; Huang, J. ; Lei, X. L. ; Wu, M. S. ; Liu, G.; Ouyang, C. Y.; Xu, B. Adsorption and Diffusion of Lithium on MoS2 Monolayer: The Role of Strain and Concentration. Int. J. Electrochem. Sci. 2013, 8, 2196–2203.

(87)

Harris, S. J.; Timmons, A.; Baker, D. R.; Monroe, C. Direct in Situ Measurements of Li Transport in Li-Ion Battery Negative Electrodes. Chem. Phys. Lett. 2010, 485, 265–274.

(88)

Liu, Y.; Artyukhov, V. I.; Liu, M.; Harutyunyan, A. R.; Yakobson, B. I. Feasibility of Lithium Storage on Graphene and Its Derivatives. J. Phys. Chem. Lett. 2013, 4, 1737– 1742.

(89)

Fan, X.; Zheng, W. T.; Kuo, J.-L.; Singh, D. J. Adsorption of Single Li and the Formation of Small Li Clusters on Graphene for the Anode of Lithium-Ion Batteries. ACS Appl. Mater. Interfaces 2013, 5, 7793–7797.

(90)

Garay-Tapia, A. M.; Romero, A. H.; Barone, V. Lithium Adsorption on Graphene: From Isolated Adatoms to Metallic Sheets. J. Chem. Theory Comput. 2012, 8, 1064–1071.

(91)

Lee, E.; Persson, K. A. Li Absorption and Intercalation in Single Layer Graphene and Few Layer Graphene by First Principles. Nano Lett. 2012, 12, 4624–4628.

(92)

Schimka, L.; Gaudoin, R.; Klimeš, J.; Marsman, M.; Kresse, G. Lattice Constants and Cohesive Energies of Alkali, Alkaline-Earth, and Transition Metals: Random Phase Approximation and Density Functional Theory Results. Phys. Rev. B 2013, 87, 214102.

(93)

Chowdhury, C.; Karmakar, S.; Datta, A. Capping Black Phosphorene by H-BN Enhances Performances in Anodes for Li and Na Ion Batteries. ACS Energy Lett. 2016, 1, 253–259.

(94)

Yun, W.S.; Han, S. W. Hong, S.C.; Kim, I.G.; Lee, J. D. Thickness and Strain Effects on 31 ACS Paragon Plus Environment


Electronic Structures of Transition Metal Dichalcogenides: 2H-MX2 Semiconductors (M=Mo, W; X= S, Se, Te). Phys. Rev. B 2012, 85, 033305. (95)

Li, H.; Du, M.; Mleczko, M. J.; Koh, A. L.; Nishi, Y.; Pop, E.; Bard, A. J.; Zheng, X. Kinetic Study of Hydrogen Evolution Reaction over Strained MoS2 with Sulfur Vacancies Using Scanning Electrochemical Microscopy. J. Am. Chem. Soc. 2016, 138, 5123–5129.

(96)

Li, H.; Tsai, C.; Koh, A. L.; Cai, L.; Contryman, A. W.; Fragapane, A. H.; Zhao, J.; Han, H. S.; Manoharan, H. C.; Abild-Pedersen, F.; et al. Activating and Optimizing MoS2 Basal Planes for Hydrogen Evolution through the Formation of Strained Sulphur Vacancies. Nat. Mater. 2015, 15, 48.

(97)

Peng, Q.; Wang, Z.; Sa, B.; Wu, B.; Sun, Z. Electronic Structures and Enhanced Optical Properties of Blue Phosphorene/Transition Metal Dichalcogenides van Der Waals Heterostructures. Sci. Rep. 2016, 6, 31994.

(98)

Hao, J.; Zheng, J.; Ling, F.; Chen, Y.; Jing, H.; Zhou, T.; Fang, L.; Zhou, M. StrainEngineered Two-Dimensional MoS2 as Anode Material for Performance Enhancement of Li/Na-Ion Batteries. Sci. Rep. 2018, 8, 2079.

(99) Shriver, D. F.; Atkins, P.; Langford, C. H. Inorganic Chemistry, 2nd ed.; Freeman: New York, 1994; pp 75-76. (100) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry, 3rd ed.; Wiley: New York 1972; p 720. (101) Liu, L.; Kumar, S. B.; Ouyang, Y.; Guo, J. Performance Limits of Monolayer Transition Metal Dichalcogenide Transistors. IEEE Trans. Electron Devices 2011, 58, 3042–3047. (102) Han, S.W.; Kwon, H.; Kim, S. K.; Ryu, S.; Yun, W. S.; Kim, D. H.; Hwang, J. H.; Kang, J.-S.; Baik, J.; Shin, H. J.; Hong, S. C. Band-Gap Transition Induced by Interlayer van Der Waals Interaction in MoS2. Phys. Rev. B 2011, 84, 045409. (103) Gan, L.-Y.; Zhang, Q.; Zhao, Y.-J.; Cheng, Y.; Schwingenschlögl, U. Order-Disorder Phase Transitions in the Two-Dimensional Semiconducting Transition Metal Dichalcogenide Alloys Mo1-xWxX2 (X = S, Se, and Te). Sci. Rep. 2014, 4, 6691. (104) Xi, J.; Zhao, T.; Wang, D.; Shuai, Z. Tunable Electronic Properties of Two-Dimensional Transition Metal Dichalcogenide Alloys: A First-Principles Prediction. J. Phys. Chem. Lett. 2014, 5, 285–291. (105) Gutiérrez, H. R.; Perea-López, N.; Elías, A. L.; Berkdemir, A.; Wang, B.; Lv, R.; López32 ACS Paragon Plus Environment

Page 32 of 34

Page 33 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Urías, F.; Crespi, V. H.; Terrones, H.; Terrones, M. Extraordinary Room-Temperature Photoluminescence in Triangular WS2 Monolayers. Nano Lett. 2013, 13, 3447–3454. (106) Splendiani, A.; Sun, L.; Zhang, Y.; Li, T.; Kim, J.; Chim, C.-Y.; Galli, G.; Wang, F. Emerging Photoluminescence in Monolayer MoS2. Nano Lett. 2010, 10, 1271–1275. (107) Bertolazzi, S.; Brivio, J.; Kis, A. Stretching and Breaking of Ultrathin MoS2. ACS Nano 2011, 5, 9703–9709. (108) Castellanos-Gomez, A.; Poot, M.; Steele, G. A.; van der Zant, H. S. J.; Agraït, N.; RubioBollinger, G. Elastic Properties of Freely Suspended MoS2 Nanosheets. Adv. Mater. 2012, 24, 772–775. (109) Courtney, I. A.; Tse, J. S.; Mao, O.; Hafner, J.; Dahn, J. R. Ab Initio Calculation of the Lithium-Tin Voltage Profile. Phys. Rev. B 1998, 58, 15583–15588. (110) Zheng, H.; Jiang, K.; Abe, T.; Ogumi, Z. Electrochemical Intercalation of Lithium into a Natural Graphite Anode in Quaternary Ammonium-Based Ionic Liquid Electrolytes. Carbon N. Y. 2006, 44, 203–210. (111) Yang, Z.; Choi, D.; Kerisit, S.; Rosso, K. M.; Wang, D.; Zhang, J.; Graff, G.; Liu, J. Nanostructures and Lithium Electrochemical Reactivity of Lithium Titanites and Titanium Oxides: A Review. J. Power Sources 2009, 192, 588–598. (112) Zhang, S. S.; Jow, T. R. Study of Poly(Acrylonitrile-Methyl Methacrylate) as Binder for Graphite Anode and LiMn2O4 Cathode of Li-Ion Batteries. J. Power Sources 2002, 109, 422–426.



TOC


Page 34 of 34

Monolayer Transition Metal Dichalcogenide Mo1-xWxS2 Alloys as

Recommend Documents