New Insights into the Anchoring Mechanism of Polysulfides inside

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Cite This: ACS Appl. Mater. Interfaces 2018, 10, 43896−43903

New Insights into the Anchoring Mechanism of Polysulfides inside Nanoporous Covalent Organic Frameworks for Lithium−Sulfur Batteries Xuedan Song,*,† Mengru Zhang,† Man Yao,‡ Ce Hao,† and Jieshan Qiu† †

State Key Laboratory of Fine Chemicals and ‡School of Materials Science and Engineering, Dalian University of Technology, Dalian, Liaoning 116024, China

ACS Appl. Mater. Interfaces 2018.10:43896-43903. Downloaded from pubs.acs.org by YORK UNIV on 12/19/18. For personal use only.

S Supporting Information *

ABSTRACT: The application prospects of lithium−sulfur (Li−S) batteries are constrained by many challenges, especially the shuttle effect of lithium polysulfides (Li2Sx). Recently, microporous covalent organic framework (COF) materials have been used to anchor electrodes in Li−S batteries, because of their preferable characteristics, such as self-design ability, suitable pore size, and various active groups. To identify the ideal anchoring materials that can effectively restrain the shuttle of Li2Sx species, the anchoring mechanism between COF materials and Li2Sx species should be investigated in depth. Therefore, we systematically investigated the anchoring mechanism between specific COF nanomaterials (consisting of boron and oxygen atoms and benzene group) and Li2Sx (x = 1, 2, 4, 6, or 8) species on the surface and inside the pore using density functional theory methods with van der Waals interactions. The detailed analysis of the adsorption energy, difference charge density, charge transfer, and atomic density of states can be used to determine that the COF nanomaterials, with the structure of boroxine connecting to benzene groups and boroxine groups not constructed at the corner of the structure, can effectively anchor the Li2Sx series. Accordingly, this study provides the theoretical basis for the molecular-scale design of ideal anchoring materials, which can be useful to improve the performance of the Li−S batteries. KEYWORDS: lithium−sulfur batteries, shuttle effect, nanoporous materials, covalent organic frameworks, Li2Sx species, first-principles simulation

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materials,24−26 covalent organic framework (COF) materials,27−31 and so forth. COFs have received great attention for their application as anchoring cathode materials for Li−S batteries because of their preferable characteristics in various active sites, suitable pore size, self-design ability, large specific surface area, and small density. From 2014 to 2016, nitrogen (N)-doped COFs have been used to sulfur cathode materials, such as CTF-1, PorCOF, Py-COF, and Azo-COF.27−29 Then, Yoo et al. adopted the composite structure of microporous COF-1 [boron (B), oxygen (O)-doped] grown on a mesoporous carbon nanotube as new interlayer cathode materials in Li−S batteries experimentally. Meanwhile, in this study, they mainly analyzed the adsorption phenomenon of Li2S on the COF-1 using DFT and grand canonical Monte Carlo calculations and emphasized that the chemical affinity for chemical trapping of Li2S is caused by the boron atom of COF-1.31 After that, Ghazi et al. directly adopted COF-1 as cathode materials in Li−S batteries

INTRODUCTION With the increasing energy demand of modern society, lithium−sulfur (Li−S) batteries have attracted considerable attention because of their exceptional theoretical capacity (1672 mA h g−1) and high theoretical energy density (2600 W h kg−1).1−5 Moreover, because of the many advantages of sulfur, such as light weight, high natural abundance, low cost, and environmental friendliness, Li−S batteries have been recognized as the potential energy storage systems for commercial applications in the future.6,7 As noted above, Li−S batteries have numerous advantages; however, Li−S batteries face many challenges, including low Coulombic efficiency, poor cycle life, and so forth.8−12 One of the reasons for some of these challenges is the shuttle effect caused by the intermediate polysulfide products dissolved in the electrolyte during the charge and discharge processes, which leads to the loss of reactant sulfur.13,14 In recent years, many researchers have put forward various solutions to solve this problem, from the perspectives of electrolytes,15,16 SEI films,17,18 to cathode materials.19−31 Some of them adopted nanoporous materials as the anchoring material, such as carbon nanotubes,19,20 metal oxides,21−23 metal organic framework © 2018 American Chemical Society

Received: September 17, 2018 Accepted: November 27, 2018 Published: November 27, 2018 43896

DOI: 10.1021/acsami.8b16172 ACS Appl. Mater. Interfaces 2018, 10, 43896−43903

Research Article

ACS Applied Materials & Interfaces

energy, difference charge density, Bader charge, and atomic density of states, we found that boroxine and benzene groups of COF-PA (adsorption energy, Eads = −3.8 to −0.7 eV) are easier to interact with the Li2Sx species during the lithiation process than COF-PB (Eads = −3.6 to −0.3 eV), and the COF nanomaterials, with relatively little steric hindrance and the structure of boroxine connecting to benzene groups, can effectively anchor the Li2Sx series, which provides the theoretical basis for the design of ideal cathode materials to restrain the shuttle effect of Li2Sx species.

experimentally, which showed a relatively stable cycle life in the charge−discharge processes.30 Till now, there is an urgent but few-reported problem: the systematic anchoring mechanism for restraining the shuttle effect of polysulfides by COF nanomaterials is ambiguous. The COF composites generally contain N, B, and O atoms and benzene groups. Because of the influence of the electronegativity, the activity of the B−O polar bond generated by the interaction of the positive B atom with the negative O atom is higher than that of the N−N nonpolar bond. The benzene group, with a large electron cloud density resulting from the conjugate π orbital electron that may interact with Li2Sx, could be an important active site to restrain the loss of polysulfides. Accordingly, we concentrated on two common active groups as research objects, consisting of B and O atoms, namely, the active boroxine group and active pentacyclic group (consisting of the boronate ester bond O−B−O bonded to an aromatic ring). Thus, we constructed two COFs, one consisting of boroxine and benzene groups, termed as COFPA, and the other consisting of an active pentacyclic group and a benzene group, termed as COF-PB, as shown in Figure 1a,b.

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METHODS

Our calculations are carried out using DFT with the VASP33 under GGA with PBE exchange-correlation functional.34 The frozen-core PAW method is adopted to describe the ion−electron interactions.35 Particularly, we choose the optPBE-vdW functional36,37 to account for the vdW interactions after making the functional tests in Table S1. Self-consistent field calculations are performed with a convergence criterion of 1 × 10−4 eV per atom. The cutoff energy is set to 520 eV, and the magnitude of the force on atoms is minimized to be less than 0.05 eV Å−1. To simulate both surface and inside pore adsorption between Li2Sx species and the modeled COFs, the six-layer constructions of COF-PA and COF-PB are constructed through the total energy and electronic computations, and the vacuum is sufficiently set to 20 Å in the z-direction. The optimized structures of COF-PA, COF-PB, and Li2Sx (x = 1, 2, 4, 6, or 8) species are shown in Figure 1a−c, respectively. To describe the interaction between Li2Sx species and the modeled COFs, the Eads can be calculated as Eads = ECOFs − Li2Sx − ECOFs − E Li2Sx

(1)

where ECOFs−Li2Sx, ECOFs, and ELi2Sx represent the total energy for the adsorption system of Li2Sx species with the modeled COFs, COFs (COF-PA or COF-PB), and Li2Sx species, respectively. To have an evident view of charge transfer between Li2Sx and the modeled COFs, the charge density difference Δρ can be defined as

Δρ = ρCOFs − Li S − ρCOFs − ρLi S 2 x

2 x

(2)

where ρCOFs−Li2Sx, ρCOFs, and ρLi2Sx represent the charge density for the adsorption system of Li2Sx species with the modeled COFs, COFs, and Li2Sx species, respectively.

Figure 1. Constructions of (a) COF-PA and (b) COF-PB are used as anchoring materials, (c) molecule configurations for Li2Sx species from Li2S to unlithiated S8 at various lithiation stages, which are all optimized with optPBE-vdW method. Color scheme: O, red; C, gray; B, pink; H, white; S, yellow; and Li, purple.

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RESULTS AND DISCUSSION To obtain the relatively stable active sites for surface adsorption, we selected the surface adsorption between Li2S2 and COF-PA as the research objects. All possible adsorption sites of COF-PA were considered, including B, O, and benzene active sites, as shown in Figure 2a. Adsorption patterns consisted of specific atoms of Li2S2 molecule anchored on specific adsorption sites of COF-PA, and seven possible cases were considered, as shown in Table 1. After comparing the adsorption energy, the energetically more favorable partial adsorption configurations were confirmed as Ap-2 and Ap-3 patterns [Figure 2(b,c)], whose adsorption energies are −2.97 and −2.95 eV, respectively. Accordingly, we considered the adsorption patterns of Ap-2 and Ap-3 separately to compare the Li2Sx adsorption properties on the surfaces of COF-PA and COF-PB. The Li2Sx species, including Li2S8, Li2S6, Li2S4, Li2S2, and Li2S, were considered, because they represent the lithiation/delithiation processes. First, the stable Ap-2 and Ap-3 adsorption configurations of the Li2Sx species on the surface of the modeled COFs were calculated and are shown in Figures S3 and S4, and the partial adsorption configurations around adsorption sites are shown in

COF-PA and COF-PB are modeled by referring to the construction of COF-1 and COF-5 synthesized by Yaghi et al.32 The theoretical XRD patterns of COF-PA and COF-PB in bulk state after optimization are simulated and shown in Figure S1, which fits well with experimental XRD data.32 It should be noted that COF-PA is somewhat different from COF-1: the pore size of COF-1 is 0.7 nm because of its AB-staggered stacking arrangement, but the constructed COF-PA has AA stacking arrangement with a pore size of 1.5 nm, as shown in Figure S2. Considering the key factor of pore effect in most COFs and making the universal but useful conclusion on the adsorption function of the B, O, and benzene active sites in normal COFs, we have constructed the COF-PA structure. In our studies, systematic calculations of the interaction mechanism between Li2Sx (x = 1, 2, 4, 6, or 8) species, as shown in Figure 1c, and the modeled COFs on both the surface and inside the pore were performed by the DFT method. On the basis of the comparison of the adsorption 43897


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Because the adsorption energy values of Li2S4 and Li2S6 are relatively small, we take the adsorption system of Li2S4 and Li2S6 on the modeled COFs as examples. Their charge density differences in the Ap-2 and Ap-3 patterns are shown in Figure S5, and the charge density differences around adsorption sites are shown in Figure 4a−d. First, in the Ap-2 pattern, the charge transfer between COF-PA and Li2S4 (or Li2S6) is larger than that between COF-PB and Li2S4 (or Li2S6), which indicates that it is easier for COF-PA to generate chemical bonds between COF-PA and Li2Sx species. Meanwhile, charge is lost along the Li−S bond in the Li2Sx (blue part) to COFPA, which means that charge was transferred from Li2Sx to COF-PA. Second, in the Ap-3 pattern, the charge exchange between COF-PB and Li2S4 (or Li2S6) is significantly increased compared with that in the Ap-2 pattern, almost comparable to the charge exchange between COF-PA and Li2S4 (or Li2S6). Moreover, it is obvious that the charge exchange between Li2Sx species and the active benzene group plays an important role in chemical bond generation. To further investigate the charge transfer quantitatively, we selected Li2S4 and Li2S6 as examples, using the Bader charge method to calculate the number of valence electrons of the atoms in Li2Sx and the COFs in the Ap-2 and Ap-3 patterns, as shown in Table 2. The positive (negative) value of the charge transfer means gain (loss) charge; the Δe(Li) values are very small, whereas the Δe(S) values are much larger, which suggests that the chemical interaction is derived from the electron transfer between the S atoms in Li2Sx into the COFs. A detailed analysis shows that, in the Ap-2 pattern, the electron is dominantly captured by the O atom of COFs, and the ability to capture electrons of the O atom in COF-PA is better than that of the O atom in COF-PB, which increased electrostatic interactions. For the Ap-3 pattern, the analysis reveals that the electron is dominantly captured by the benzene group of COFs, and whether in the COF-PA or in COF-PB, the ability of the benzene group to capture the charge is strong. In general, COF-PA, with O−B hexatomic rings and active benzene groups, can effectively capture the electron and thus enhances the anchoring effect. In addition, to understand the nature of the chemical bonding between Li2Sx species and the COFs, analysis of the atomic partial density of states (PDOS) near the Fermi energy region was performed. The Li2S4 with the COF-PA was chosen to elucidate the difference in electronic structure in the Ap-2 and Ap-3 patterns, as shown in Figure 4e,f. The PDOS of the Li2S4 and COF-PA system in the Ap-2 pattern shown in Figure 4e indicates that the main orbital interactions of the Li2S4 and COF-PA system are between the Li1-2s and O1-2p orbitals and between the Li2-2s and O2-2p orbitals around the Fermi energy level. Additionally, no obvious overlapping is observed between the Li-2s and Ben-pz orbitals. The PDOS of the Li2S4 and COF-PA system in the Ap-3 pattern shown in Figure 4f reveals that, besides the hybridization between the Li1-2s and the O1-2p orbitals, there is an even stronger hybridization between the Li2-2s and Ben-pz orbitals. Similar interpretations can be given for the orbital interactions of the Li2S4 and COFPB system in the Ap-2 and Ap-3 patterns, as shown in Figure S6. To sum up, the analyses of the electronic structure and charge transfer further explain and agree well with the difference in adsorption energies between Li2Sx species and the modeled COFs. Because there are many regular pores in COF structures, we also considered the adsorption inside the pore, which was

Figure 2. (a) Illustration of different adsorption sites in COF-PA. The energetically more favorable partial configurations of Li2S2 molecule on the surface of COF-PA (b) in Ap-2 pattern and (c) in Ap-3 pattern. Color scheme: O, red; C, gray; B, pink; H, white; S, yellow; and Li, purple.

Table 1. Adsorption Energy or Final Adsorption Pattern between Li2S2 and COF-PA of Seven Different Kinds of Adsorption Pattern sites adsorption pattern Ap-1 Ap-2 Ap-3 Ap-4 Ap-5 Ap-6 Ap-7

O-a

O-b

B-a

Li1 Li1 Li1

Li2

S1

B-b

Ben-m

Li2 Li1 Li1 S1 S1

Li2 S2

Eads (eV) or final adsorption pattern −0.71 −2.97 −2.95 Ap-2 Ap-3 −0.82 Ap-2

Figure 3a−d. In addition, their simulated adsorption energies are presented in Figure 3e. From a general perspective, the adsorption strengths of the Li2Sx species and COF-PA (−3.8 to −0.7 eV) are clearly lower than those of the Li2Sx species and COF-PB (−3.6 to −0.3 eV). This indicates that, regardless of the Ap-2 or Ap-3 adsorption style, COF-PA has stronger interactions with the Li2Sx species during the lithiation process. A comparison of the adsorption energy curves of the Ap-2 and Ap-3 patterns reveals that the adsorption energy values in the Ap-3 pattern are generally lower than that in the Ap-2 pattern whether in COF-PA or in COF-PB. It is worth noting that the adsorption energy values of Li2S4 and Li2S6 with COF-PB in the Ap-3 pattern decreased by 0.5 and 0.4 eV, respectively, compared with that in the Ap-2 pattern. This means that in the Ap-3 pattern, the combination of O and benzene active sites plays an important role in increasing the adsorption interaction of the Li2Sx species. By Bader charge method,38,39 the Bader charge curves of the Li2Sx species at various lithiation stages in the Ap-2 and Ap-3 patterns are shown in Figure 3f. The curves reveal that the tendency of electron transfer from the Li2Sx species to the COFs is quite consistent with the adsorption energy curves, which is the reason why the adsorption energies of the Ap-2 and Ap-3 patterns have different values. On the basis of the stable adsorption configurations described above, the visualized difference in the charge transfer could be obtained by calculating the charge density difference. 43898


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Figure 3. Illustration of stable partial adsorption configurations of Li2Sx (x = 1, 2, 4, 6, or 8) series adsorbed on the surface of COF-PA (a) in Ap-2 pattern and (b) in Ap-3 pattern and of COF-PB (c) in Ap-2 pattern and (d) in Ap-3 pattern after optimization. (e) The adsorption energy curves and (f) the Bader charge curves of Li2Sx species and the modeled COFs in Ap-2 and Ap-3 adsorption patterns. The negative value of Bader charge means lose electron for Li2Sx species. Color scheme: O, red; C, gray; B, pink; H, white; S, yellow; and Li, purple.

Li2Sx (x = 4, 6) and COF-PA range from −0.6 to −0.8 eV, and the adsorption energies of Li2S4 and COF-PB range from −0.3 to −0.5 eV, which are comparable to the magnitude of the surface adsorption energies. In particular, the adsorption energy between Li2S6 and COF-PB in the Ap-b pattern is lower (about 0.5 eV) than that on the surface, and even lower (about 0.45 eV) than that between Li2S6 and COF-PA in the Ap-b pattern. The Bader charge analyses clearly establish that the Bader charges are consistent with the adsorption energies inside the pore. To further understand the distinct adsorption energies of the Li2S6 anchored in the pore of the COF-PA and COF-PB in the Ap-b patterns, the charge density difference was simulated and

performed by active sites across the layers. On the basis of the electronegativity, we considered two possible adsorption patterns inside the pore, namely, the Ap-a and Ap-b patterns, as shown in Figure 5. The Ap-a pattern represents the interaction pattern between the Li atoms in Li2Sx and the active O atoms in the COFs. The Ap-b represents the interaction pattern between the S atoms in Li2Sx and the active benzene groups in the COFs. The stable adsorption configurations of the Li2Sx (x = 4, 6) anchored in the pore of the COF-PA and COF-PB in the Ap-a and Ap-b patterns were calculated and are shown in Figure 5 and Figure S7, respectively. In addition, their simulated adsorption energy and Bader charge are listed in Table 3. The adsorption energies of 43899


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Figure 4. Illustrations of charge density difference of Li2Sx (x = 4, 6) adsorbed on the COF-PA (a) in Ap-2 pattern and (b) in Ap-3 pattern and on the COF-PB (c) in Ap-2 pattern and (d) in Ap-3 pattern. Here, blue regions mean losing charge, and red regions mean gaining charge. Atomic PDOS near the Fermi energy region for Li2S4 adsorbed on the surface of COF-PA (e) in Ap-2 pattern and (f) in Ap-3 pattern. Among them, Ben means active benzene group.

Table 2. Bader Charge Differences of Li2Sx (x = 4, 6) Molecule Adsorbed on Different Atoms of the COFs in Ap-2 and Ap-3 pattern Δe(Li2Sx)

Δe(COFs)

Adsorption pattern

Li2Sx

Δe(Li)

Δe(S)

Δe(O)

Δe(B)

COF-PA-Ap-2

Li2S4 Li2S6 Li2S4 Li2S6 Li2S4 Li2S6 Li2S4 Li2S6

−0.004 0.004 −0.003 −0.001 −0.004 0.012 −0.005 0.005

−0.090 −0.118 −0.021 −0.006 −0.185 −0.103 −0.140 −0.022

0.081 0.091 0.012 −0.044 0.066 0.030 0.060 −0.026

−0.064 −0.008 0.003 0.000 0.002 −0.029 0.006 −0.010

COF-PB-Ap-2 COF-PA-Ap-3 COF-PB-Ap-3

Δe(C)

Δe(Li2Sx) = −Δe(COFs)

0.262 0.373 0.378 0.393

−0.094 −0.114 −0.024 −0.007 −0.189 −0.091 −0.145 −0.017

PB, can contribute to anchoring Li2Sx species. In addition, we also considered the solvent effect on adsorption interaction of Li2Sx and COFs inside the pore as shown in Figure S10. It indicates that, in the presence of the DME solvent, the adsorption interaction of Li2S4 and COFs is enhanced, which means the shuttle effect of polysulfide dissolution is well suppressed. In addition, the reaction potential at the active site of COFs was calculated, and the free energy diagram for the reaction coordination in the Li−S battery is shown in Figure 7. After the calculation of the Gibbs free energy of reaction, the main

is shown in Figures S8 and S9, and the pictures for charge density difference around adsorption sites are shown in Figure 6a,b. The simulations reveal that the change density difference can be visually illustrated by the relatively little steric hindrance of the COF-PB compared with that of COF-PA in Ap-b pattern. This increases the interaction between Li2S6 and the active sites (O and benzene) in two adjacent layers of COFPB, thus augmenting the charge exchange between Li2S6 and COF-PB from the charge density difference analysis in Figure 6b. To summarize, the adsorption caused by the active sites across the layers in the pore, whether in COF-PA or in COF43900


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Figure 5. Illustrations of the stable adsorption configurations of the Li2S4 anchored in the pore of the COF-PA (a) in the Ap-a pattern and (b) in Ap-b pattern and the Li2S6 anchored in the pore of the COF-PA (c) in the Ap-a pattern and (d) in Ap-b pattern.

Table 3. Adsorption Energy and the Bader Charge of Li2Sx (x = 4, 6) and the Modeled COFs in Ap-a and Ap-b Adsorption Patterns Bader chargea (e)

Eads (eV) Li2S4

Li2S6

Li2S4

Li2S6

COF

Ap-a

Ap-b

Ap-a

Ap-b

Ap-a

Ap-b

Ap-a

Ap-b

COF-PA COF-PB

−0.61 −0.30

−0.72 −0.45

−0.63 −0.33

−0.77 −1.23

−0.043 −0.019

−0.059 −0.024

−0.030 −0.022

−0.058 −0.063

a

The negative value of Bader charge means lose electron for Li2Sx species.

Figure 7. Illustration of the free energy diagram for reaction coordination at different active sites of COF-PA and COF-PB.

the free energy diagram, it is concluded that the free energy of reaction of S8 converting into Li2S4 on the COF-PA is larger than that on the COF-PB, which means S8 is easier to convert into Li2S4 on the COF-PA than on the COF-PB during the charge and discharge processes. Meanwhile, Ap-3 adsorption style can make S8 easier to convert into Li2S4. This means a lot, because the shuttle effect is caused by Li2Sx (x = 4, 6, 8) dissolved in the electrolyte during the discharge processes. Hence, it further confirms the conclusion above.

Figure 6. Illustrations of charge density difference of Li2S6 adsorbed in the pore of (a) the COF-PA and (b) the COF-PB in Ap-b pattern. Here, blue regions mean losing charge, and red regions mean gaining charge.

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CONCLUSIONS In summary, we systematically investigated the mechanism of constraining the shuttle effect of Li2Sx (x = 1, 2, 4, 6, 8) species

reactions at the different active sites of COFs (COF-PA and COF-PB) for sulfur reduction can be summarized as follows: S8 → 2(Li2S4) → 4(Li2S2) → 8(Li2S). Through the analysis of 43901



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anchored by COF-PA (consisting of active boroxine and benzene groups) and COF-PB (consisting of active pentacyclic and active benzene groups), by DFT calculations with vdW interactions. From the surface adsorption perspective, we filtered out two relatively stable adsorption patterns, AP-2 (two Li atoms interacting with two O atom active sites in the COFs, separately) and AP-3 (two Li atoms interacting with O, benzene active sites in the COFs, separately). The adsorption energy of anchoring Li2Sx species shows that, in general, COFPA is better than COF-PB, and the AP-3 adsorption pattern plays an important role in increasing the adsorption interaction of the Li2Sx species. Through the thorough analyses of the charge density difference and Bader charge, it is determined that the active O atoms in the boroxine and benzene groups are the main contributors to the adsorption of Li2Sx (x = 4, 6) species. In addition, the PDOS confirms the above conclusion. From the perspective of the adsorption inside the pore, the adsorption energy of COF-PB with Li2S6 inside the pore (Eads = −1.02 eV) is lower than that on the surface (Eads = −0.03 eV) because of the relatively small steric hindrance of the COF-PB resulting from the exposure of active sites. Accordingly, the COF nanomaterials, with the structure of boroxine connecting to benzene groups and boroxine groups not constructed at the corner of the structure, can effectively adsorb Li2Sx species. Therefore, our study provides the theoretical basis for the molecular-scale design of ideal anchoring materials for restraining the shuttle effect of Li2Sx species, which can be useful for improving the performance of Li−S batteries.

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REFERENCES

(1) Chiang, Y.-M. Building a Better Battery. Science 2010, 330, 1485−1486. (2) Zhang, S.; Ueno, K.; Dokko, K.; Watanabe, M. Recent Advances in Electrolytes for Lithium−Sulfur Batteries. Adv. Energy Mater. 2015, 5, 1500117. (3) Manthiram, A.; Chung, S.-H.; Zu, C. Lithium−Sulfur Batteries: Progress and Prospects. Adv. Mater. 2015, 27, 1980−2006. (4) Zhang, K.; Qin, F.; Lai, Y.; Li, J.; Lei, X.; Wang, M.; Lu, H.; Fang, J. Efficient Fabrication of Hierarchically Porous GrapheneDerived Aerogel and Its Application in Lithium Sulfur Battery. ACS Appl. Mater. Interfaces 2016, 8, 6072−6081. (5) Zhang, Y.-Z.; Zhang, Z.; Liu, S.; Li, G.-R.; Gao, X.-P. FreeStanding Porous Carbon Nanofiber/Carbon Nanotube Film as Sulfur Immobilizer with High Areal Capacity for Lithium−Sulfur Battery. ACS Appl. Mater. Interfaces 2018, 10, 8749−8757. (6) Bruce, P. G.; Freunberger, S. A.; Hardwick, L. J.; Tarascon, J.-M. Li−O2 and Li−S Batteries with High Energy Storage. Nat. Mater. 2012, 11, 19−29. (7) Wang, J.-G.; Xie, K.; Wei, B. Advanced Engineering of Nanostructured Carbons for Lithium−sulfur Batteries. Nano Energy 2015, 15, 413−444. (8) Jand, S. P.; Chen, Y.; Kaghazchi, P. Comparative theoretical study of adsorption of lithium polysulfides (Li2Sx) on pristine and defective graphene. J. Power Sources 2016, 308, 166−171. (9) Ji, X.; Nazar, L. F. Advances in Li−S Batteries. J. Mater. Chem. 2010, 20, 9821−9826. (10) Scrosati, B.; Garche, J. Lithium batteries: Status, prospects and future. J. Power Sources 2010, 195, 2419−2430. (11) Manthiram, A.; Fu, Y.; Chung, S.-H.; Zu, C.; Su, Y.-S. Rechargeable Lithium−sulfur Batteries. Chem. Rev. 2014, 114, 11751−11787. (12) Fang, R.; Zhao, S.; Sun, Z.; Wang, D.-W.; Cheng, H.-M.; Li, F. More Reliable Lithium−Sulfur Batteries: Status, Solutions and Prospects. Adv. Mater. 2017, 29, 1606823. (13) Liang, X.; Hart, C.; Pang, Q.; Garsuch, A.; Weiss, T.; Nazar, L. F. A Highly Efficient Polysulfide Mediator for Lithium−sulfur Batteries. Nat. Commun. 2015, 6, 5682. (14) Wang, J.; He, Y.-S.; Yang, J. Sulfur-Based Composite Cathode Materials for High-Energy Rechargeable Lithium Batteries. Adv. Mater. 2015, 27, 569−575. (15) Natarajan, A.; Stephan, A. M.; Chan, C. H.; Kalarikkal, N.; Thomas, S. Electrochemical Studies on Composite Gel Polymer Electrolytes for Lithium Sulfur-Batteries. J. Appl. Polym. Sci. 2017, 134, 44594. (16) Fu, K.; Gong, Y.; Xu, S.; Zhu, Y.; Li, Y.; Dai, J.; Wang, C.; Liu, B.; Pastel, G.; Xie, H.; Yao, Y.; Mo, Y.; Wachsman, E.; Hu, L. Stabilizing the Garnet Solid-Electrolyte/Polysulfide Interface in Li−S Batteries. Chem. Mater. 2017, 29, 8037−8041. (17) Nandasiri, M. I.; Camacho-Forero, L. E.; Schwarz, A. M.; Shutthanandan, V.; Thevuthasan, S.; Balbuena, P. B.; Mueller, K. T.; Murugesan, V. In Situ Chemical Imaging of Solid-Electrolyte Interphase Layer Evolution in Li−S Batteries. Chem. Mater. 2017, 29, 4728−4737. (18) Li, G.; Huang, Q.; He, X.; Gao, Y.; Wang, D.; Kim, S. H.; Wang, D. Self-Formed Hybrid Interphase Layer on Lithium Metal for High-Performance Lithium−Sulfur Batteries. ACS Nano 2018, 12, 1500−1507. (19) Zhao, Y.; Wu, W.; Li, J.; Xu, Z.; Guan, L. Encapsulating MWNTs into Hollow Porous Carbon Nanotubes: A Tube-in-Tube Carbon Nanostructure for High-Performance Lithium−Sulfur Batteries. Adv. Mater. 2014, 26, 5113−5118. (20) Qie, L.; Manthiram, A. A Facile Layer-by-Layer Approach for High-Areal-Capacity Sulfur Cathodes. Adv. Mater. 2015, 27, 1694− 1700. (21) Kim, J.-S.; Hwang, T. H.; Kim, B. G.; Min, J.; Choi, J. W. A Lithium-Sulfur Battery with a High Areal Energy Density. Adv. Funct. Mater. 2014, 24, 5359−5367.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.8b16172. Theoretical XRD patterns of COFs in bulk state after optimization; illustrations of stable configurations of COF-1 in AA stacking arrangement and AB stacking arrangement (COF-PA); optimized construction and the charge density difference of Li2Sx species adsorbed on the modeled COFs in detail; illustrations of atomic PDOS for Li2S4 adsorbed on the surface of COF-PB; functional correction of vdW interactions tests (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Xuedan Song: 0000-0001-7531-4344 Man Yao: 0000-0002-7322-9258 Ce Hao: 0000-0002-4379-0474 Jieshan Qiu: 0000-0002-6291-3791 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work has been supported by the National Natural Science Foundation of China (Grant nos. 21606040 and 21677029), the Fundamental Research Funds for the Central Universities (DUT18LK26), the Supercomputing Center of Dalian University of Technology, and the National Supercomputing Center in LvLiang of China. 43902


Research Article

ACS Applied Materials & Interfaces (22) Seh, Z. W.; Yu, J. H.; Li, W.; Hsu, P.-C.; Wang, H.; Sun, Y.; Yao, H.; Zhang, Q.; Cui, Y. Two-dimensional Layered Transition Metal Disulphides for Effective Encapsulation of High-Capacity Lithium Sulphide Cathodes. Nat. Commun. 2014, 5, 5017. (23) Liu, X.; Huang, J.-Q.; Zhang, Q.; Mai, L. Nanostructured Metal Oxides and Sulfides for Lithium−Sulfur Batteries. Adv. Mater. 2017, 29, 1601759. (24) Zhou, J.; Li, R.; Fan, X.; Chen, Y.; Han, R.; Li, W.; Zheng, J.; Wang, B.; Li, X. Rational Design of a Metal−Organic Framework Host for Sulfur Storage in Fast, Long-Cycle Li−S Batteries. Energy Environ. Sci. 2014, 7, 2715−2724. (25) Mao, Y.; Li, G.; Guo, Y.; Li, Z.; Liang, C.; Peng, X.; Lin, Z. Foldable Interpenetrated Metal-Organic Frameworks/Carbon Nanotubes Thin Film for Lithium-Sulfur Batteries. Nat. Commun. 2017, 8, 14628. (26) Bai, S.; Liu, X.; Zhu, K.; Wu, S.; Zhou, H. Metal−Organic Framework-Based Separator for Lithium−Sulfur Batteries. Nat. Energy 2016, 1, 16094. (27) Liao, H.; Ding, H.; Li, B.; Ai, X.; Wang, C. Covalent-Organic Frameworks: Potential Host Materials for Sulfur Impregnation in Lithium−Sulfur Batteries. J. Mater. Chem. A 2014, 2, 8854−8858. (28) Liao, H.; Wang, H.; Ding, H.; Meng, X.; Xu, H.; Wang, B.; Ai, X.; Wang, C. A 2D Porous Porphyrin-Based Covalent Organic Framework for Sulfur Storage in Lithium−Sulfur Batteries. J. Mater. Chem. A 2016, 4, 7416−7421. (29) Yang, X.; Dong, B.; Zhang, H.; Ge, R.; Gao, Y.; Zhang, H. Sulfur Impregnated in a Mesoporous Covalent Organic Framework for High Performance Lithium−Sulfur Batteries. RSC Adv. 2015, 5, 86137−86143. (30) Ghazi, Z. A.; Zhu, L.; Wang, H.; Naeem, A.; Khattak, A. M.; Liang, B.; Khan, N. A.; Wei, Z.; Li, L.; Tang, Z. Efficient Polysulfide Chemisorption in Covalent Organic Frameworks for High-Performance Lithium−Sulfur Batteries. Adv. Energy Mater. 2016, 6, 1601250. (31) Yoo, J.; Cho, S.-J.; Jung, G. Y.; Kim, S. H.; Choi, K.-H.; Kim, J.H.; Lee, C. K.; Kwak, S. K.; Lee, S.-Y. COF-Net on CNT-Net as a Molecularly Designed, Hierarchical Porous Chemical Trap for Polysulfides in Lithium−Sulfur Batteries. Nano Lett. 2016, 16, 3292−3300. (32) Cóté, A. P.; Benin, A. I.; Ockwig, N. W.; O’Keeffe, M.; Matzger, A. J.; Yaghi, O. M. Porous, Crystalline, Covalent Organic Frameworks. Science 2005, 310, 1166−1170. (33) Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for Ab Initio Total-Energy Calculations Using a Plane-Wave Basis Set. Phys. Rev. B. 1996, 54, 11169−11186. (34) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865−3868. (35) Blochl, P. E. Projector Augmented-wave Method. Phys. Rev. B. 1994, 50, 17953−17979. (36) Dion, M.; Rydberg, H.; Schrö der, E.; Langreth, D.C.; Lundqvist, B.I. Van der Waals Density Functional for General Geometries. Phys. Rev. Lett. 2004, 92, 246401. (37) Klimeš, J.; Bowler, D. R.; Michaelides, A. Chemical Accuracy for the Van der Waals Density Functional. J. Phys.: Condens. Matter 2010, 22, 022201. (38) Henkelman, G.; Arnaldsson, A.; Jónsson, H. A Fast and Robust Algorithm for Bader Decomposition of Charge Density. Comput. Mater. Sci. 2006, 36, 354−360. (39) Tang, W.; Sanville, E.; Henkelman, G. A Grid-Based Bader Analysis Algorithm Without Lattice Bias. J. Phys. Condens. Matter. 2009, 21, 084204.

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New Insights into the Anchoring Mechanism of Polysulfides inside

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