Edge effects on Li atom adsorption and migration of MoS2 zigzag nanoribbons

Applied Surface Science 494 (2019) 223–229

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Edge effects on Li atom adsorption and migration of MoS2 zigzag nanoribbons

T

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Yan-Ni Wena, , Peng-Fei Gaob, Hui-Hui Yanga, Xiao Tiana, Wen-Jia Danga, Cheng-Xi Hua, ⁎ Sheng-Li Zhangb, a b

Xi'an Aeronautical University, Shannxi 710077, People's Republic of China Department of Applied Physics, School of Science, Xi'an Jiaotong University, 710049, People's Republic of China

A R T I C LE I N FO

A B S T R A C T

Keywords: Edge effects Adsorption Migration MoS2 Nanoribbon First-principles

In this paper, the effects of the two edges, i.e., S and Mo terminals for zigzag MoS2 nanoribbons, on Li atom adsorption and migration were studied from first principles. The lattice constants of NRs are width-dependent. The adsorption energy of single or multi-lithium adatoms is stronger when they are bound to the top of Mo atoms and when a Li atom is closer to the edge of a nanoribbon, particularly the S terminal edge. The symmetric twosided adsorption configuration is more to form for multi-lithium adatoms. In addition, Li atoms initially adsorbed at the S or Mo terminal edge always prefer to diffuse along their corresponding edges. For other ones, they prefer to diffuse towards their nearby S or Mo terminal edge. These results indicate that zigzag MoS2 nanoribbons can significantly increase the Li binding energy while providing a high mobility path for Li. We hope our theoretical studies will inspire experimental studies on zigzag MoS2 nanoribbons for use as cathode materials.

1. Introduction At present, Li ion batteries (LIBs) are one of the most mature energy storage technologies. They have been widely used in all walks of life after several years of rapid growth [1]. They provide high electrical storage capacity, high charging and discharging rates, and safety without environmental pollution [2]. In recent years, LIBs are being developed to have lower costs, higher storage capacity and high power, and longer life cycle. However, the electrode in a LIB is a crucial part of battery design and innovation of battery materials [3]. Extensive research has focused on the use of two-dimensional (2D) materials like MoS2, which can provide high specific capacity, long cyclic stability, high discharge rate, and safety [4–6]. For example, MoS2/graphene nanocomposites showed high specific capacity of 1400 mAh/g during the first cycle and specific capacity of 1351 mAh/g after 200 cycles [4]. A nanoflower MoS2 anode decorated with crumpled reduced graphene oxides exhibited high specific capacity (1225 mAh/ g) and cycling performance (680 mAh/g) after 250 cycles [5]. Ultrathin MoS2 nano-layers on N-doped carbon shells showed high specific capacity of ~1000 mAh/g [6]. These results indicate that MoS2 is a potentially useful material for anodes in LIBs. Quasi-one-dimensional (Q1D) structures offer a range of potential

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applications that are quite different from those offered by their 2D counterparts [7–9]. For example, Yang et al. found that MoS2 nanoribbons (NRs) may be a promising cathode material for use in rechargeable Mg batteries [10]. Li et al. found that the zigzag edge state with 100% and 50% S coverage in MoS2 NRs may provide stronger binding interaction with Li atoms [11]. However, in their calculations, the lattice parameters within the ribbons remained nearly unchanged compared to the corresponding 2D material. This may lead to some unreasonable results [7]. In addition, two kinds of boundary structures are often considered, i.e., S terminal (100% S coverage) and Mo terminal (no S coverage), when studying the properties of MoS2 NRs [12,13]. These gaps in the literature drive us to study the effects of S and Mo terminal edges on adsorption and migration of Li when the lattice parameters are optimized. In this paper, we first optimized the lattice constant of the NRs based on calculations from first principles. We then found that a single Li adatom is bound to the top of a Mo atom in a MoS2 NR, and the adsorption energy is stronger when a Li atom is closer to the edge of an NR, particularly the S terminal edge. Next, we found that the symmetric two-sided adsorption configuration is more to form for two Li adatoms, particularly at the S terminal edge too. Finally, diffusion of single Li adatoms was studied. We found if a Li atom is first adsorbed at a S or

Corresponding authors. E-mail addresses: [email protected] (Y.-N. Wen), [email protected] (S.-L. Zhang).

https://doi.org/10.1016/j.apsusc.2019.07.112 Received 15 February 2019; Received in revised form 29 June 2019; Accepted 14 July 2019 Available online 19 July 2019 0169-4332/ © 2019 Elsevier B.V. All rights reserved.

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terminals in 7-ZZ-MoS2 NR was studied. According to the edge structure of a ZZ-MoS2 NR shown in Fig. 2(a), seven (1–7 and 1′–7′) adatom positions were considered in our initial models for S and Mo terminals edges, respectively. After structural optimization, a Li adatom at sites 3 and 7 evolved to sites 1 and 6 at the S terminal, respectively, while a Li adatom at sites 1′, 2′, or 3′ evolved to sites 4′, 5′, or 7′ at the Mo terminal, respectively. There are four and five typical positions respectively for Mo and S terminals, respectively, as shown in Fig. 2(b) and (c). The corresponding adsorption energies were listed in Table1. From Table 1, one finds that the maximum adsorption energies 3.75 eV and 3.11 eV appeared at the top of Mo for the S and Mo terminals in a 7-ZZ-MoS2 NR. This indicates that a Li adatom is bound to the top of Mo whether in a MoS2 NR or 2D MoS2. For comparison, the adsorption energy of a Li adatom at the top of another Mo atom (a–d) in the middle of an NR shown in Fig. 2(a) was calculated, and the result is listed in Table 1. Fig. 3 shows the adsorption energy with a Li adatom sited on top of a different Mo atom in a 7-ZZ-MoS2 NR. The lowest point of the curve corresponds to the minimum adsorption energy. From Fig. 3, one can see that the adsorption energy is stronger when a Li atom is closer to the edge of the NR, particularly the S terminal edge. However, these values are all larger than the value for 2D MoS2 (1.70 eV). This illustrates that MoS2 NRs absorb Li more easily compared to 2D monolayer MoS2 structures due to the existence of edges. However, regarding the S terminal in a 7-ZZ-MoS2 NR, this result is different from that found in Ref. [11], in which the maximum adsorption energies appeared between symmetric S atoms near 6. This is attributed to the fact that the lattice constants in a 7-ZZ-MoS2 NR changed to 3.153 Å. For further explanation, the adsorption energies a Li adatom at the top of a Mo atom (1 site as in Fig. 2) and between symmetric S atoms (6 site as in Fig. 2) were calculated using 3.183 Å as the lattice constant in 7-ZZ-MoS2 NR, and adsorption energies of 3.28 and 3.54 eV were obtained for 1 and 6 sites, respectively. Obviously, the same results found in Ref. [11] can be obtained without considering a change in the lattice constant. This shows that the lattice constants of NRs are width-dependent. Next, we focus on adsorption of more Li atoms on MoS2 NRs. The structural properties of two adjacent adsorbed atoms were investigated at the edges in a 7-ZZ-MoS2 NR. When the first Li adatom is adsorbed on top of a Mo atom (sites 1 or 7′) at a S or Mo terminal, three sites (1s, d, and 1N) or four sites (7s′, a, 1′, and 7N′) should be considered for the second Li adatom, as shown in Fig. 2(a). The subscript ‘s’ indicates symmetric sites for a Li adatom about a Mo atom, and the subscript ‘N’ indicates the nearest neighbor to the 1 or 7′ site along the ribbon axis. Table 2 list the adsorption energies of the two Li atoms sited at the S (upper row) and Mo (lower row) terminals in a 7-ZZ-MoS2 NR. From Table 2, one can see that the adsorption energies 6.98 and 5.57 eV are the maximum values for the S and Mo terminals in a 7-ZZMoS2 NR, respectively. This indicates the symmetric two-sided adsorption configuration is more to form for two Li adatoms, particularly at a S terminal. However, the second most advantageous adsorption structure is a 1-1N and 7′-7N′ structure for two Li adatoms at S and Mo terminals, respectively. Thus, one can infer that multiple Li adatoms always prefer symmetric adsorption on each edge in an NR, particularly for the S terminal edge.

Mo terminal edge, it will prefer to diffuse along the corresponding edge. However, if a Li atom is first adsorbed at a site near the S edge, then it will prefer to diffuse towards the S edge, otherwise it will diffuse towards the Mo edge. A detailed discussion can be found in Section 3. 2. Methods In this work, all calculations were performed from first-principles using spin-polarized DFT with the projector augmented wave method [14,15]. All calculations were implemented with the Vienna ab initio simulation package (VASP) [16]. The generalized gradient approximation (GGA) and the Perdew-Burke-Ernzerhof (PBE) functional were used to describe electron exchange correlation interactions [17,18]. The cut-off of the plane-wave kinetic energy and convergence of the total energy were set to 400 eV and 10−5 eV, respectively. In order to eliminate interactions between neighboring nanoribbons, a vacuum region of at least 20 Å was defined along the two directions perpendicular to the ribbon axis. The Monkhorst and Pack k-point sampling scheme with 9 × 1 × 1 grids was used for Brillouin zone integration [19]. The geometrical structures were fully optimized with the lattice vectors and atomic positions being relaxed under a force convergence of 0.02 eV/Å. In our previous study [8], zigzag MoS2 nanoribbons (ZZ-MoS2 NRs) with seven zigzag MoeS chains along the ribbon length (7-ZZ-MoS2 NR) were used as representative models to study their various properties. In order to simplify our calculations in this study, we only considered the 7-ZZ-MoS2 NR when we study the edge effects on Li adsorption and migration in the ZZ-MoS2 NRs. However, three supercells can provide sufficient distance to suppress interactions between Li adatoms. This equates to a computing cell for a 7-ZZ-MoS2 NR with 63 atoms without Li atoms. We found that the optimized lattice constant for a 7-ZZ-MoS2 NR is 3.153 Å. The computing cell is shown in Fig. 1. 3. Results and discussion 3.1. Structural properties of MoS2 NRs with Li adatoms We first studied adsorption of single Li atom on 2D MoS2. Many theoretical [20–22] and experimental studies [23,24] referred to the potential binding sites for Li or other metal atoms on 2D MoS2. Their findings lead us to consider the following three adsorption sites for a Li adatom on 2D MoS2 in our initial calculations: top of a Mo atom (Motop), top of a S atom (S-top), and the center of the six rings (valley-top). After structural optimization, the adsorption energies were calculated using the following equation [20]:

Eads = E MoS2 + nELi − EnLi + MoS2 where EMoS2 and EnLi+MoS2 are the total energies of the unit cell with and without n Li adatoms, respectively, and ELi is the energy of a free Li atom. The values 1.70 eV, 1.01 eV, and 1.54 eV were obtained for a Li adatom adsorbed at Mo-top, S-top, and valley-top, respectively. A Li atom is most easily adsorbed at Mo-top in 2D MoS2 because this site has largest energy value, which consistent with results from previous studies [20,22]. Then the adsorption of a single lithium atom at the S and Mo

3.2. Diffusion of Li adatoms It is known that the charging/discharging rate of an electrode is determined by its electrical conductivity and Li diffusion. Therefore, it is very important to understand diffusion of a Li adatom on a MoS2 NR. We used the static relaxation method to determine the minimum energy path and saddle points. We chose the two nearest neighboring Mo atoms for their energetic favorability. The initial and final states were constructed by adsorbing a Li atom on top of a Mo atom (T1 and T2(N), where N is refers to a different Mo atom close to the edge), and then fully structural optimized. Seven intermediate images with equal

Mo-terminal S-terminal

Fig. 1. Computing cell of a 7-ZZ-MoS2 NR. There are 7 zigzag MoeS chains along the width of the NR. Purple blue balls: Mo; yellow balls: S. 224

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Fig. 2. (a) Initial sites at Mo terminal, S terminal, and in the middle of a 7-ZZ-MoS2 NR for Li adatoms. Intermediate graph (Top graph) viewed along the c axis and bilateral graphs (Side graphs) viewed along the b axis. (b) and (c) Optimized Li adatom sites at the Mo and S terminals, respectively. Side and Top graphs are viewed along the b axis and c axis for Mo and S terminals, respectively. 1–7 and 1′–7′ refer to adsorption sites for Li at the S and Mo terminals, respectively. Purple blue balls: Mo; yellow balls: S; green balls: Li.

calculations (0.24 eV) [22]. Fig. 4(b) and (d) show that the minimum potential barrier for Li migration from the top of a Mo atom to its nearest neighbor are 0.31 eV and 0.47 eV for the S and Mo terminals in a 7-ZZ-MoS2 NR, respectively. This indicates an Li atom that is initially adsorbed at the S or Mo edge will prefer to diffuse along the S edge or Mo edge, respectively. From Fig. 4(c), the potential barrier for Li migration from the top of the middle Mo atom to its nearest neighbor close to the S terminal in a 7ZZ-MoS2 NR is 0.18 eV. However, if a Li atom is first adsorbed at an a site, as shown in Fig. 2(a), Fig. 4(b) shows that the potential barrier for Li migration from a to its nearest neighbor close to the Mo terminal in a 7-ZZ-MoS2 NR is 0.22 eV. These results indicate that Li atoms will prefer to migrate along the edge by crossing activation barriers. If the Li atom

intervals were linearly chosen between them, as shown in Fig. 4. Fig. 4(a) shows the transport path of a Li atom from Tl to T2(N) (black rough lines). However, it was mentioned in Ref. [21] that the optimal Li diffusion path is from a T1 (Mo-top) site to the nearest neighboring T2 (Mo-top) site passing through the center of the six-membered ring (valley site, viz. V-top) near T1. Fig. 4(b)–(d) shows the calculated energy profiles along the different paths for one Li atom adsorbed at the S terminal (S-T), Mo terminal (Mo-T), and in the middle (M-T) of a 7ZZ-MoS2 NR, respectively. For comparison, a single Li atom diffused at the 2D surface of MoS2 was also calculated and is shown in Fig. 4(e). The energy at the initial position (site T1) was set to 0 in all diffusion energy calculations. The calculated diffusion energy (0.23 eV) for a single Li adatom is consistent with the results from previous

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Table 1 Adsorption energies of Li adatoms at the S (labeled by the number up the diagonal line in the upper row) and Mo (labeled by the number below the diagonal line in the upper row) terminals, and in the middle of a 7-ZZ-MoS2 NR (labeled with a-d up the diagonal line in the lower row) with the one Li on the 2D surface (labeled Motop, S-top, and valley-top below the diagonal line in the lower row).

Energy (eV)

1/4′

2/5′

4/6′

5/7′

a/Mo-top

b/S-top

c/Vally-top

d

S terminal

3.75

3.44

3.50

3.52

3.64

Mo terminal

2.87

2.05

2.14

3.11

–

Middle

2.73

2.76

2.99

3.04

2.99

2D

1.70

1.01

1.54

Site

6

as shown in Fig. 5(b) and (c). For Mo-edge, the adsorption energies 3.03, 3.45, 3.53, 3.35, 3.27, and 2.59 eV can be calculated for a Li adatom at sites 1M, 2M, 3M (4M), 5M (8M), 6M, and 7M, respectively. After sorting the energy values from small to large, one can see that 2.59 eV (7M) < 3.03 eV (1M) < 3.27 eV (6M) < 3.35 eV (5M) < 3.45 eV (2M) < 3.53 eV (3M). For S-edge, the adsorption energies 2.76, 2.72 and 2.89 eV can be calculated for a Li adatom at sites 2M′ (3M′), 5M′ (6M′), 4M′ (1M′ or 7M′), respectively. The site with the highest energy has the strongest adsorption capacity. We found that Li most easily adsorbs on the top of the edge between two S atoms (3M (4M)) and two Mo atoms (4M′ (1M′ or 7M′)), respectively for the Mo- and S-edge. Combined with the previous calculation results, we find that different edge structures lead to different adsorption behavior for Li atoms. However, these values are all larger than the adsorption energy on 2D MoS2 (1.70 eV). This again illustrates that MoS2 NRs more easily absorb Li atoms than the corresponding 2D monolayer structures due to the existence of edges. Fig. 3. Adsorption energies with a Li adatom on top of different Mo atoms in a 7-ZZ-MoS2 NR.

4. Conclusions

is first adsorbed at a site near the S edge, then it will prefer to diffuse towards the S edge, otherwise it will diffuse towards the Mo edge. However, defects are inevitably introduced during the 2D MoS2 fabrication processes [25]. Moreover, numerous works have shown that the Mo and S edge morphologies are affected by temperature and the presence of impurities [26–30]. Typical conditions in a LIB could significantly affect adsorption and diffusion of a Li adatom on 2D MoS2 or a MoS2 NR. To illustrate this point, the edges of a 7-ZZ-MoS2 NR were modified to match the configuration in Ref. [30], and the adsorption behavior of a single Li atom on Mo- or S-edges was studied. Eight (1M-8M) and seven (1M′-7M′) adatom positions were considered in our initial models respectively based on the Mo- and S-edge structure, as shown in Fig. 5(a). After structural optimization, Li adatoms at sites 3M and 5M on the Mo-edge evolved to sites 4M and 8M, respectively. And Li adatoms at sites 3M′, 6M′ and 1M′ or 7M′ on the Sedge evolved to sites 2M′, 5M′ and 4M′, respectively. There are six and three typical positions for Li adatom respectively on a Mo- and S-edges,

In this study, the effects of S and Mo terminals on Li adsorption and migration along two edges in MoS2 NRs were systematically investigated from first principles using spin-polarized DFT and the projector augmented wave method. We found that a single Li adatom is bound to the top of a Mo atom in a MoS2 NR, and the adsorption energy is stronger when a Li atom is closer to the edge of an NR, particularly the S terminal edge. The symmetric two-sided adsorption configuration is more to form for two Li adatoms, particularly at the S terminal. If the Li atom is first adsorbed at a S or Mo edge, then it will prefer to diffuse along the S or Mo edge, respectively. However, if a Li atom is first adsorbed at a site near the S edge, then it will prefer to diffuse towards the S edge, otherwise it will diffuse towards the Mo edge. A ZZ-MoS2 NR can provide significantly higher binding energy for Li while preserving high mobility for Li adatoms. Therefore, ZZ-MoS2 NRs are promising cathode materials for use in Li-ion batteries. We hope our theoretical studies will inspire experimental studies on ZZ-MoS2 NRs for use as cathode materials. The edge structures shown in Fig. 1 were

Table 2 Adsorption energies of two adjacent adsorbed Li atoms at the S and Mo terminals in a 7-ZZ-MoS2 NR.

Energy (eV) Site

1-1N

1-d

–

1-1s

7′-7N′

7′-a

7′-1′

7′-7s′

S-terminal

6.71

6.29

–

6.98

Mo-terminal

5.23

5.13

4.93

5.57

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Fig. 4. (a) Different diffusion paths for a single Li atom migrating across a Mo-top site to valley-top to a Mo-top site. (b)–(e) Energy as a function of reaction coordinate for each pathway T1-T2 (N). The Mo terminal, S terminal, and the middle of a 7-ZZ-MoS2 NR are abbreviated Mo-T, S-T, and M-T, respectively.

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c

b

a

(a)

(b)

(c) Fig. 5. (a) Initial sites at Mo terminal, S terminal, and in the middle of a 7-ZZ-MoS2 NR for Li adatoms. Top graph viewed along the c axis and Side graphs viewed along the b axis. (b) and (c) Optimized Li adatom sites at the Mo and S terminals, respectively. Side and Top graphs are viewed along the b axis and c axis for Mo and S terminals, respectively. 1M–8M and 1M′-7M′ refer to adsorption sites for Li at the Mo and S terminals, respectively. Purple blue balls: Mo; yellow balls: S; green balls: Li.

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investigated in detail in this study. Other complex structures will be examined in greater detail in the future.

neighbor hopping, Phys. Rev. B 98 (2018) 075202. [13] O. Ávalos-Ovando, D. Mastrogiuseppe, S.E. Ulloa, Lateral interfaces of transition metal dichalcogenides: a stable tunable one-dimensional physics platform, Phys. Rev. B 99 (2019) 035107. [14] J.P. Perdew, K. Burke, M. Ernzerhof, Generalized gradient approximation made simple, Phys. Rev. Lett. 77 (1996) 3865–3868. [15] G. Kresse, D. Joubert, From ultrasoft pseudopotentials to the projector augmentedwave method, Phys. Rev. B 59 (1999) 1758–1775. [16] G. Kresse, J. Furthmüller, Efficient iterative schemes for ab-inition total-energy calculations using a plane-wave basis set, Phys. Rev. B 54 (1996) 11169–11186. [17] P. Hohenberg, W. Kohn, In homogeneous electron gas, Phys. Rev. B 136 (1964) 864–871. [18] P.E. Blöchl, Projector augmented-wave method, Phys. Rev. B 50 (1994) 17953–17979. [19] H.J. Monkhorst, J.D. Pack, Special points for Brillouin-zone integrations, Phys. Rev. B 13 (1976) 5188–5192. [20] D.B. Putungan, S.H. Lin, C.M. Wei, J.L. Kuo, Li adsorption, hydrogen storage and dissociation using monolayer MoS2: an ab initio random structure searching approach, Phys. Chem. Chem. Phys. 17 (2015) 11367–11374. [21] F. Ersan, G. Gökoğlu, E. Aktürk, Adsorption and diffusion of Li on monolayer transition metal dichalcogenides (MoS2(1−x)Se2x) alloys, J. Phys. Chem. C 119 (2015) 28648–28653. [22] D.N. Esfahani, O. Leenaerts, H. Sahin, B. Partoens, F.M. Peeters, Structural transitions in monolayer MoS2 by lithium adsorption, J. Phys. Chem. C 119 (2015) 10602–10609. [23] H. Li, S. Wang, H. Sawada, G.G.D. Han, T. Samuels, C.S. Allen, A.I. Kirkland, J.C. Grossman, J.H. Warner, Atomic structure and dynamics of single platinum atom interactions with monolayer MoS2, ACS Nano 11 (2017) 3392–3403. [24] E. Cha, M.D. Patel, J. Park, J. Hwang, V. Prasag, K. Cho, W. Choi, 2D MoS2 as an efficient protective layer for lithium metal anodes in high-performance Li-S batteries, Nat. Nanotechnol. 13 (2018) 337. [25] X. Sun, Z. Wang, Y.Q. Fu, Defect-mediated lithium adsorption and diffusion on monolayer molybdenum disulfide, Sci. Rep. 5 (2015) 18712. [26] B. Baubet, M. Girleanu, A.S. Gay, A.L. Taleb, M. Moreaud, F. Wahl, V. Delattre, E. Devers, A. Hugon, O. Ersen, P. Afanasiev, P. Raybaud, Quantitative two-dimensional (2D) morphology-selectivity relationship of CoMoS nanolayers: a combined high-resolution high-angle annular dark field scanning transmission electron microscopy (HR HAADF-STEM) and density functional theory (DFT) study, ACS Catal. 6 (2016) 1081–1092. [27] P. Raybaud, Understanding and predicting improved sulfide catalysts: insights from first principles modeling, Appl. Catal. A Gen. 322 (2007) 76–91. [28] J.F. Paul, S. Cristol, E. Payen, Computational studies of (mixed) sulfide hydrotreating catalysts, Catal. Today 130 (2008) 139–148. [29] M. Badawi, S. Cristol, J.F. Paul, E. Payen, DFT study of furan adsorption over stable molybdenum sulfide catalyst under HDO conditions, C. R. Chim. 12 (2009) 754–761. [30] M. Badawi, J.F. Paul, S. Cristol, E. Payen, Y. Romero, F. Richard, S. Brunet, D. Lambert, X. Portier, A. Popov, E. Kondratieva, J.M. Goupil, J.E. Fallah, J.P. Gilson, L. Mariey, A. Travert, F. Maugé, Effect of water on the stability of Mo and CoMo hydrodeoxygenation catalysts: a combined experimental and DFT study, J. Catal. 282 (2011) 155–164.

Acknowledgments This work was supported by the National Natural Science Foundation of China (NSF) (Grants Nos. 11774278, 10704059, 11774280, 11374237), Shaanxi Provincial Science and Technology Department, China (2019JM-447), Shaanxi Province Postdoctoral Science Foundation, China (2016BSHEDZZ78), Education Department of Shaanxi Province, China (17JK0394). References [1] M.L. Li, J. Luo, W.D. Wang, Compare investigation of lithiation, sodiation, and magnesiation ion adsorptions and diffusions on monolayer MoS2 for energy storages using first-principles, Proceedings of the 17th IEEE International Conference on Nanotechnology Pittsburgh, USA, July 25-28, 2017. [2] L. Lu, X. Han, J. Li, J. Hua, M. Ouyang, A review on the key issues for Li-ion battery management in electric vehicles, J. Power Sources 226 (2013) 272–288. [3] R. Marom, S.F. Amalraj, N. Leifer, D. Jacob, D. Aurbach, A review of advanced and practical Li battery materials, J. Mater. Chem. 21 (2011) 9938–9954. [4] Y.C. Liu, Y.P. Zhao, L.F. Jiao, J. Chen, A graphene-like MoS2/graphene nanocomposite as a high performance anode for Li ion batteries, J. Mater. Chem. A 2 (2014) 13109–13115. [5] F. Xiong, Z. Cai, L. Qu, P. Zhang, Z. Yuan, O.K. Asare, W. Xu, C. Lin, L. Mai, Threedimensional crumpled reduced graphene oxide/MoS2 nanoflowers: a stable anode for Li-ion batteries, ACS Appl. Mater. Interfaces 7 (2015) 12625–12630. [6] X.Y. Yu, H. Hu, Y.W. Wang, H.Y. Chen, X.W. Lou, Ultrathin MoS2 nanosheets supported on N-doped carbon nanoboxes with enhanced Li storage and electrocatalytic properties, Angew. Chem. Int. Ed. 54 (2015) 7395–7398. [7] Y.N. Wen, P.F. Gao, X. Chen, M.G. Xia, Y. Zhang, S.L. Zhang, Width-dependent structural stability and magnetic properties of monolayer zigzag MoS2 nanoribbons, Mod. Phys. Lett. B 31 (2017) 1750017. [8] Y.N. Wen, M.G. Xia, S.L. Zhang, Structural and magnetic properties of MoS2 monolayer zigzag nanoribbon doped by Ti, V, Cr, and Mn, Phys. Lett. A 382 (2018) 2354–2360. [9] Y.N. Wen, M.G. Xia, S.L. Zhang, Size effect on the magnetic and electronic properties of the monolayer lateral hetero-junction WS2-MoS2 nanoribbon, Appl. Surf. Sci. 371 (2016) 376–382. [10] S. Yang, D. Li, T. Zhang, Z. Tao, J. Chen, First-principles study of zigzag MoS2 nanoribbon as a promising cathode material for rechargeable Mg batteries, J. Phys. Chem. C 116 (2012) 1307–1312. [11] Y. Li, D. Wu, Z. Zhou, C.R. Cabrera, Z. Chen, Enhanced Li adsorption and diffusion on MoS2 zigzag nanoribbons by edge effects: a computational study, J. Phys. Chem. Lett. 3 (2012) 2221–2227. [12] A.C. Dias, F. Qu, D.L. Azevedo, J. Fu, Band structure of monolayer transition-metal dichalcogenides and topological properties of their nanoribbons: next-nearest-

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