SnS2 Nanoparticles on Graphene

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Rationally Incorporated MoS2/SnS2 Nanoparticles on Graphene Sheets for Lithium-ion and Sodium-ion Batteries Yong Jiang, Yibo Guo, WenJun Lu, Zhenyu Feng, Baojuan Xi, Shuangshuang Kai, Junhao Zhang, Jinkui Feng, and Shenglin Xiong ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b06572 • Publication Date (Web): 01 Aug 2017 Downloaded from http://pubs.acs.org on August 1, 2017

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ACS Applied Materials & Interfaces

Rationally Incorporated MoS2/SnS2 Nanoparticles on Graphene Sheets for Lithium-Ion and SodiumIon Batteries Yong Jiang,a Yibo Guo,a Wenjun Lu,a Zhenyu Feng,a Baojuan Xi, *,a Shuangshuang Kai,a Junhao Zhangb, Jinkui Feng,c Shenglin Xiong*,a a

Key Laboratory of the Colloid and Interface Chemistry, Ministry of Education, and School of

Chemistry and Chemical Engineering, Shandong University, Jinan, 250100, PR China b

School of Environmental and Chemical Engineering, Jiangsu University of Science and

Technology, Zhejiang, Jiangsu, 212003, P.R. China c

Key Laboratory for Liquid-Solid Structural Evolution & Processing of Materials (Ministry of

Education), School of Materials Science and Engineering, Shandong University, Jinan 250061, PR China

KEYWORDS: graphene • SnS2 • MoS2 • Na-ion batteries • Li-ion batteries

ACS Paragon Plus Environment

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ABSTRACT: Herein, we have designed and first synthesized a unique ternary hybrid structure by simultaneously growing SnS2 and MoS2 particles on graphene sheets (denoted as MoS2/SnS2GS) via one-pot hydrothermal route. The charge incompatibility between MoO42- as Mo source and graphene oxide with negative charged functional groups on surface can be compromised with the aid of Sn4+ cations, which renders the final in-situ formation of SnS2 and MoS2 on GS surface. Here, it’s the first time to report the co-hybridization of MoS2 and SnS2 with GS matrix from anionic and cationic precursors in the absence of pre-mediation of graphene surface. When MoS2/SnS2-GS acts as anodes for lithium-ion batteries, the hybrids exhibit much better cycling stability than MoS2-GS and SnS2-GS counterparts. The compact adhesion of MoS2/SnS2 nanoparticles helps offset the undesired result of destruction of electrode materials resulting from volume expansion during repeated cycles. Furthermore, by combination with their synergetic effect on interface and the presence of discrepant asynchronous electrochemical reactions for SnS2 and MoS2, MoS2/SnS2-GS hybrids are endowed with improvement of electrochemical capabilities. Besides, they also showed outstanding Na-storage ability.

INTRODUCTION Lithium-ion batteries (LIBs) were applied as the major power source for portable electronic devices in the past decades. In recent years, as electrified transportation has developed rapidly, the present commercial LIBs can not be competent for the extensive application of electric vehicles due to the low energy storage ability and the expensive cost. Considering the fact1,2 that the graphite which is ubiquitously applied in commercial LIBs has a low theoretical capacity of


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372 mA h g-1, explorations of new electrode materials with high energy/power densities for nextgeneration energy storage devices are very urgent. Layered metal dichalcogenides (LMDs), such as MoS2, SnS2, SnS and WS2, have been widely researched as potential anode candidates for LIBs, as well as Na-ion batteries (NIBs).2-15 This is generally ascribed to their higher specific capacity of LMDs comparing with graphite. Moreover, these sulfides with characteristic layered structure have a large interlayer spacing which greatly favors the migration of guest species and relief of the volume variations during cycling.12 However, the intrinsic low-conductivity of these LMDs and the surviving volume changes usually disable the competence in respect of capacity, cycle stability and rate ability which are quantitative indicators assessing a new electrode material. To circumvent these obstacles, combination of these LMDs with carbon matrix is an effectively developed solution. Among the multitudinous carbon matrixes, two-dimensional (2D) carbon materials (i.e. graphene) with the strong mechanical flexibility and excellent electronic conductivity have good structural compatibility with LMDs. These merits of graphene impart the outstanding electrochemical performance to the hybrid materials comprising LMDs and graphene. For example, our group reported the SnS2 ultrafine nanocrystals bonded on amino-functionalized graphene, showing enhanced cycling stability.4 Qu et al.12 synthesized SnS2-reduced graphene oxide hybrid (SnS2RGO) for NIB anode material. Relative to the disappointed performance of pristine SnS2, SnS2RGO improved sodium storage ability was borne by reduced graphene oxide (RGO). Zhou et al.13 examined SnS@graphene as anode for NIBs which showed a reversible capacity of ~940 mAh g-1 at 30 mA g-1. Hybrids, wherein MoS2 sheets were distributed on graphene, verified a striking Li+ storage ability, which was attributed to the synergistic interaction on the interfaces of the two components.14


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Such integration of graphene and LMDs has been a common concept in the design of this kind of hybrid anodes. Although the microstructure and morphology are compatible between RGO and LMDs,14 the abundant oxygen-containing groups render GO highly negatively charged which results in the repulsion between GO and anionic precursor of LMDs (MoO42-, WO42-, MoS42- and other similarity) in the solution. The charge incompatibility leads to the unfortunate problem that the obtained LMDs cannot uniformly match with RGO. Cationic surfactants, such as cetyltrimethylammonium bromide (CTAB), are picked out as a layer of modifier to make RGO surface positive charged. Hence, the adsorption of the above precursor species can be ensured, with the result of generation of crystals on GO surface. Such hybrid examples are MoS2-graphene and MoS2/WS2-nitrogen doped graphene.14,16 Recently, Teng et al. adjusted the surface charge of GO by facilely controlling the pH of GO suspension to prepare MoS2/graphene lamellar structure.17 As well known, the homogeneous SnS2-graphene hybrids can be easily prepared without addition of any surfactant because of the electrostatic interaction of Sn4+ (or Sn2+) and functional groups on graphene surface.5,18,19 In the connection, the adsorption of Sn4+cations definitely neutralize negative charges on GO surface and the formation of SnS2 nuclei will promote the neutralization trend, which paves an alternative possibility to anchor anionic precursor of LMDs. Hence, bi-component LMDs including SnS2 and other LMDs with anionic precursors can be incorporated to attain the composite of graphene. Relying on the above conception, herein, we exploited the capacity of a hydrothermal reaction to form the hybrid composed of double LMDs and graphene sheets, namely MoS2 and SnS2 nanocrystals simultaneously and uniformly grown on graphene nanosheets (MoS2/SnS2-GS), without the pre-modification. Depending on the role of Sn4+ cations, MoO42- ions were successfully anchored onto graphene surface to grow into MoS2. Based on the results and


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analyses, Sn4+ ions are reasonably proposed to play dual role of precursor for SnS2 and providing a chance to bridge MoO42- and graphene matrix. The one-pot method is successfully applied to realize in-situ formation of SnS2 and MoS2 nanoparticles simultaneously from anionic and cationic precursors onto RGO surface for the first time. Cyclic voltammetry result displays that some primary electrochemical reactions of SnS2 and MoS2 occur at different potentials, avoiding the serious volume change. The heterostructure shows the superior lithium ion storage performance to SnS2-GS and MoS2-GS. When examined as an anode material for LIBs, MoS2/SnS2-GS electrode indicates high reversible capacity of 1244 mA h g-1 at 0.15 A g-1 after 190 cycles and excellent rate capability. Besides, it also exhibits improved sodium storage ability. EXPERIMENTAL SECTION Synthesis of graphene oxide (GO). GO was prepared from the natural graphite powder through a modified Hummers’ method.20 In a typical synthesis procedure, GO was obtained through filtering and subsequently washed with diluted HCl solution for three times. Then GO was dispersed in deionization water after being sonicated for about 1.5 h. The homogeneous suspension was dialyzed in ultrapure water for about ten days to remove the acid and the metal ions. Synthesis of MoS2/SnS2-GS, MoS2-GS and SnS2-GS. The synthesis of MoS2/SnS2-GS hybrids was performed through one-pot hydrothermal route. Firstly, the obtained Graphene Oxide (60 mg) suspension was diluted to 50 mL with deionization water and sonicated for about another 30 min to assure the homogeneous dispersion. Then 421 mg (1.2 mmol) SnCl4.5H2O was added and vigorously stirred for about one hour. After that, 194 mg Na2MoO4.2H2O (0.8 mmol) was introduced into the above mixture and kept stirring for another one hour. Successively, 510 mg


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thioacetamide (TAA) was poured under stirring. After TAA was completely dissolved, the mixture was transferred to a 60 mL Teflon-lined steel autoclave and heated at 200 °C in an oven for 12 h. Finally, the prepared sample was collected by centrifugation, sufficiently washed with deionization water and lyophilized for 48 h. For comparison, SnS2-GS and MoS2-GS were prepared based on the similar procedures to MoS2/SnS2-GS, except that 2 mmol SnCl4.5H2O and 2 mmol Na2MoO4.2H2O were used as reagent, respectively. Materials characterization. The structure and morphology of the prepared samples were characterized by various measurement techniques. X-ray powder diffraction (XRD) profiles of the obtained samples were conducted on a Bruker D8 advanced X-ray diffractometer with Cu Kα radiation (λ= 1.5418 Å). The scanning electron microscopy (SEM) images were obtained using Hitachi S-4800 SEM operated at 5 kV. Transmission electron microscopy (TEM) images, high-resolution TEM (HRTEM) images, and elemental mappings were obtained on a JEM2100F operated at 200 kV. X-ray photoelectron spectroscopy (XPS) spectra were tested by ESCALAB 250 spectrometer (Perkin-Elmer). Raman spectra were detected using a JY LABRAM-HR confocal laser micro-Raman spectrometer with 514.5 nm wavelength at room temperature. The element ratios analysis of MoS2/SnS2-GS composites was performed on inductively coupled plasma-atomic emission spectrometer (ICP-AES, IRIS Intrepid II XSP). The thermogravimetric analysis (TGA) was tested using TA Q 600 thermal analyzer in air at an increasing rate of 10 °C min-1 from room temperature to 850 °C. Electrochemical measurement. The mixture composed of the as-obtained MoS2/SnS2-GS composites (80 wt.%), carbon black (10 wt.%) and carboxymethyl cellulose binder (10 wt.%, Aladdin) was wet-ground together with the addition of the appropriate amount of deionized


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water. Then the mixture was vigorously ground into homogeneous slurry. After that, the slurry was uniformly coated onto the surface of the commercial Cu foil to acquire the electrode slice with the thickness of about 200 µm. The prepared electrode slice was then kept at 60 °C under vacuum overnight to thoroughly evaporate the solvent. Finally, the dried electrode slice was cut into disks with the diameter of 12 mm. The average mass of the loaded MoS2/SnS2-GS materials on each disk was about 1.3 mg cm-2. The CR2032 coin-type cells were assembled in a glove box under the protection of ultra-argon (O2 < 0.5 ppm, H2O < 2 ppm). For LIB test, the commercial Celgard 2400 film was employed as the separator, and the electrolyte comprised 1 M LiPF6 in mixed solvent of ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) (EC:DEC:DMC=1:1:1, volume ratio). The half cells with lithium as the counter electrode were tested on LAND CT-2001A instrument (Wuhan, China) after being aged for at least 12 hours. The galvanostatic measurements were conducted at room temperature between 0.01 V and 3.0 V. Cyclic voltammetry (CV) profiles were carried out on an electrochemistry workstation (CH 760D, Shanghai, China). The preparation process of electrodes made of MoS2-GS and SnS2GS was the same as MoS2/SnS2-GS composites. For NIB test systems, the used separator was the glass fiber (Whatman). 1 M NaClO4 was dissolved in ethylene carbonate and diethylene carbonate with the addition of 5 wt% fluoroethylene carbonate (FEC) to act as the electrolyte. The cycling tests at different current densities were measured on the LAND CT-2001A in the potential range of 0.01 V-3.0 V versus Na+/Na. The CV curves of MoS2/SnS2-GS electrode for NIBs were tested on electrochemistry workstation (CH 760E, Shanghai, China). All values of specific capacity for LIBs and NIBs in this paper were calculated based on the total mass of metal sulfides and GS. RESULTS AND DISCUSSION


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The synthesis of the MoS2/SnS2-GS hybrids is illustrated in Figure 1 (see experimental details). The homogeneous GO suspension was first coupled with the metal cations, Sn4+. According to previous documents, through an electrostatic interaction,5,18,19 Sn4+ could be easily adsorbed onto the surface. Hence, it was able to neutralize negative charges to some extent. Moreover, accompanying the formation SnS2 neuclei with thioacetamide as sulfur source, such neutralization would be promoted, thus making GO surface not repulsive to MoO42- ions. The neighboring region more favorably served as heterogeneous sites for MoS2 nucleation. Through hydrothermal treatment, the MoS2/SnS2-GS hybrids were achieved with SnS2 and MoS2 nanocrystals in-situ and uniformly grown on the graphene sheets in the absence of any surfactant. A control experiment was carried out under the same synthesis conditions except the absence of Sn4+ in the reaction system. The as-obtained products comprised two isolated parts of free-standing particles and sheets (Figure S1A-F) as reported by Li.21 The separation of GO and MoS2 testified the mediator role of Sn4+. For comparison, SnS2-GS hybrid was also synthesized through a similar route (Figure S1G-I). The MoS2/SnS2-GS hybrid was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which revealed that SnS2 and MoS2 nanocrystals were firmly pinned on the surface of the flexible graphene sheets (Figure 2A-C and S2). High-resolution TEM (HRTEM) image demonstrated the few-layered feature of the obtained RGO as marked by the white arrow in Figure 2D. Scanning TEM (STEM) and the corresponding energy dispersive X-ray (EDX) mappings of MoS2/SnS2-GS hybrid exhibited homogeneous spatial distribution of Sn, Mo, C, and S over the detected scope of the constructed hybrid material (Figure 2E). The X-ray diffraction (XRD) patterns of MoS2/SnS2-GS, MoS2-GS, SnS2-GS and pristine GO were used to analyze the phase composition. For pristine GO, only one peak at 12.4o was


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detected which coincided with the (002) diffraction index of GO (Figure S3). After combination with MoS2/SnS2, MoS2 or SnS2 (Figure 2F and S4), this sharp peak (12.4o) vanished confirming that the effective reduction of GO during the hydrothermal process. The XRD pattern of SnS2GS corresponded well with the layered structure of hexagonal SnS2 (JCPDS 23-0677) without no significant impurity. In the diffraction pattern of MoS2/GS composites in Figure S4, the characteristic diffraction peaks of hexagonal MoS2 (JCPDS 37-1492) were able to be observable.14,22 However, those peaks were weak and broad mainly due to the poor crystallinity of MoS2. For the hybrid of MoS2/SnS2-GS, the corresponding XRD pattern (curve b), it almost showed the similar profile to SnS2-GS (curve a). From the comparison of the standard patterns of MoS2 and SnS2, it was found that some main diffraction peaks of them were in close angle position. Moreover, the size of MoS2 and SnS2 particles with low crystallinity was very small, resulting in the broadening and weakness of diffraction peaks. Hence, those respective diffraction peaks characteristic of MoS2 and SnS2 would overlap in the MoS2/SnS2-GS composite and can’t be obviously differentiated. In order to find out the chemical valence of Sn and Mo in the MoS2/SnS2-GS composite, XPS technique was used. The full-scan spectrum in Figure 3A, the hybrid was composed of Sn, Mo, and S elements. As indicated in high-resolution Sn 3d and Mo 3d spectra in Figure 3B,C, notable peaks at 486.6 eV, 495.1 eV and 232.7 eV, 229.4 eV were associated with the signals of Sn3d5/2, Sn3d3/2 and Mo3d3/2, Mo3d5/2, respectively.11,21,23 Other two peaks located at 226.7 eV and 236.0 eV in Figure 3C were attributed to S 2s and Mo-O bond.27 The results confirmed the existence of Sn4+ and Mo4+. Moreover, inductively coupled plasma atomic emission spectrometer (denoted as ICP-AES) detected that the molar ratio of Sn:Mo was 2.32 : 1 for MoS2/SnS2-GS (Table S1). The


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MoS2/SnS2-GS contained 67.7 wt% SnS2, 25.6 wt% MoS2 and 6.7 wt% GS based on the analysis of TGA in Figure S8 and ICP-AES. The microstructure of MoS2/SnS2-GS hybrids was illustrated by the HRTEM image as shown in Figure 4A. The lattice fringes of about 0.63 nm adjacently apart agreed well with the (002) planes of MoS2. The (100) plane of MoS2 with a lattice spacing of 0.27 nm was also observed. In other domains, 0.32 and 0.29 nm originated from d(100) and d(002) of SnS2. To further confirm SnS2 and MoS2 coexisting in the prepared composites, MoS2/SnS2-GS, MoS2-GS, SnS2-GS were kept at 800 °C for 2 h under the atmosphere of H2/Ar (5 vol% H2). The obtained hybrids were named as MoS2/SnS2-GS-H2 (S-1), MoS2-GS-H2 (S-2), and SnS2-GS-H2 (S-3), respectively. As shown in Figure 4B, different from the weak XRD pattern (Figure S4), the crystallinity of MoS2GS was enhanced remarkably after annealing, corresponding to hexagonal MoS2 (JCPDS 371492). Interestingly, as for the annealed S-1, the peak at 14.3o indexed to the (002)-spacing of multilayer MoS2 crystal was unable to be observed. The set of peaks at 32.7o, 33.5o, 39.5o, 58.3o, 60.1o, 69.0o could be attributed to the hexagonal MoS2. Moreover, another set of sharp peaks at 30.6o, 32.0o, 43.9o, 44.9o, 55.3o, 62.5o, 63.8o, 64.6o, 72.4o, 73.2o, 79.5o matched well with the result of S-3 which can be attributed to tetragonal Sn. By comparison, the characteristic peaks of SnS2 vanished and tetragonal Sn emerged instead, indicating that a transformation from hexagonal SnS2 to tetragonal Sn after reduction. Two more new diffraction peaks at 8.5o and 17.3o were present which inferred the corresponding interlayer separation to be 1.03 nm and 0.51 nm, respectively, implying MoS2 dispersed in S-1 composites was single-layer as reported in other works.14,15 These interlayer spacings can be directly observed by the HRTEM images in Figure 4C. After the calcination in H2/Ar flow, SnS2 was reduced to metallic Sn. Considering a low melting temperature (231.9 oC) of Sn, it became liquid at 800 °C which may exfoliate the


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multilayer MoS2 to form the single-layer MoS2 in S-1. Figure 4D showed the Raman spectra of MoS2/SnS2-GS, MoS2-GS, SnS2-GS and GO. Obviously, two well-defined peaks were dominant in all spectra. One peak at 1325 cm-1 (D band) was classified as the defects and disordering in graphitic structure. The other peak at 1586 cm-1 (G band) was assigned to the ordered sp2-bonded carbon atoms of hexagonal lattice. In comparison with pristine GO, the intensity ratio of D to G band for MoS2/SnS2-GS, MoS2-GS, SnS2-GS was much higher. The increased value confirmed the upgrowth of defects with the introduction of LMDs.2,5,19 For MoS2/SnS2-GS before annealing, the emergence of new peak at 311 cm-1 was related to the A1g mode of SnS2 which was also revealed in SnS2-GS (Figure S5A,B). After Annealing, two prominent peaks at about 379.8 and 403.2 cm-1 displayed singleor few-layer sheets of MoS2 (Figure S5C), which agreed well with the results of XRD and HRTEM.2,14 The as-obtained MoS2/SnS2-GS hybrids are first examined as anodes for LIBs. The typical discharge and charge curves of MoS2/SnS2-GS at 0.15 A g-1 were shown in Figure 5A. The initial discharge and charge capacity was 1180.4 mA h g-1 and 994.0 mA h g-1, respectively. The Coulombic efficiency (CE) was 84.2% which was blamed on the formation of solid electrolyte interface (SEI) and the electrolyte decomposition.7,12 The CE quickly increased to 97.2% in the second cycle and kept at almost 100% during the subsequent cycles. From the second cycle onwards, the MoS2/SnS2-GS hybrid displayed a superior electrochemical performance sustaining a reversible capacity as high as 1244 mA h g-1 even after 190 cycles at 150 mA g-1 (Figure 5B). For comparison, MoS2/SnS2-GS, MoS2-GS, SnS2-GS were separately cycled at 0.75 A g-1 (being activated at 0.15 A g-1 for the initial several cycles) under identical condition. As shown Figure 5C, MoS2/SnS2-GS delivered a capacity of 772 mA h g-1 after 200 cycles. However, MoS2-GNS


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and SnS2-GNS only delivered 33 and 194 mA h g-1, respectively, both of which were much inferior than MoS2/SnS2-GS. Here, the similar behavior to transition metal oxides as LIB anodes can be observed that the specific capacity raised with cycling going on. This phenomenon can be ascribed to the emergence of gel-like polymeric layer and the electrochemical activation of the electrode materails.17,25 The superior cycling capability of MoS2/SnS2-GS can be ascribed to the synergistic interaction between MoS2 and SnS2 nanoparticles, the discrepant-electrochemical reactions of SnS2 and MoS2 which was discussed below. Moreover, the ultrasmall size of SnS2 and MoS2 in MoS2/SnS2-GS composite was another important factor which was helpful for the diffusion of lithium ion and the infiltration of the electrolyte. The rate performance of MoS2/SnS2-GS was shown in Figure 5D. With the current density increasing stepwise from 0.15 to 0.38, 0.75, 1.5 to 3.8 A g-1, the specific capacity was about 990, 890, 770, 665, and 456 mA h g-1, correspondingly. Remarkably, when the current density turns back to 0.15 A m-1, the capacity can be maintained as high as 1088 mA h g-1 after 70 cycles without any losses. The lithium storage performance of MoS2/SnS2-GS in our work was compared with related metal sulfide reported previously in Table S2. Cyclic voltammetry (CV) was conducted to investigate the electrochemistry of MoS2/SnS2-GS hybrid electrode. Figure 6A showed the first cathodic (CV) scan of MoS2-GS. The peaks at around 1.46 and 0.48 V are assigned to the intercalation of lithium ions into MoS2 and the conversion of MoS2 to Mo along with Li2S, respectively. A weak peak at 0.2 V is attributed to be the formation of SEI film.17 The peaks at 1.87 and 2.31 V in the anodic process are deduced to be related with the oxidation of Mo and Li2S.7,17,26,27,32 In the following scans, the appearance of two pronounced peaks at 2.1 and 1.42 V signifies a different discharge process from the first cycle.17 It is inferred that a mixture of MoS2, Mo, and sulfur act as the electrode material after the


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first cycle while only MoS2 is for the initial cycle.17 After the first cycle, the peak associated with reduction of LixMoS2 to Mo is imperceptible. In the first reduction process of SnS2-GS (Figure 6C), four peaks at 1.81, 1.62, 1.47 and 1.16 V are considered as the transformation of SnS2 to Sn and Li2S which can be decomposed into several steps.28,29 The solid electrolyte interface (SEI) is also formed near at 1.16 V resulting in the large irreversibility in the first cycle.5 The cathodic peak below 0.4 V and the anodic peak at 0.5 V represent the reversible alloying/dealloying reaction of Sn.5,30 Another two anodic peaks at 1.91 and 2.34 V belong to the oxygenation reaction of metallic tin.31 As shown in Figure 6E, the distinct CV peaks of MoS2/SnS2-GS are the summation of MoS2-GS and SnS2-GS on the whole, indicating that SnS2 and MoS2 both contributed to the specific capacity. The discharge/charge profiles of MoS2/SnS2-GS, MoS2-GS, and SnS2-GS (Figure 6) are in good accord with results of CVs. It’s noted that some dominant reactions of SnS2 and MoS2 occur at different potentials. For example, the reversible alloying and dealloying processes of Sn take place below 0.4 V and near 0.5 V, accompanied with the large volume change. However, for MoS2, no remarkable redox reactions happen at the vicinity of the above two potentials. That’s to say, the two components undergo asynchronously electrochemical reaction. Hence, the volume variation during cycling can be effectively relieved which is an indispensable factor for the excellent cycling stability of MoS2/SnS2-GS hybrid. The discharge/charge profiles of MoS2-GS (Figure 6B), SnS2-GS (Figure 6D), and MoS2/SnS2-GS (Figure 6F) confirmed the results and analyses of CV. Given the viewpoint that the NIBs was promising in large-scale application, the sodium storage capacity of MoS2/SnS2-GS was also evaluated in present study via CV testing. As shown in Figure S7, in the first discharge process, a weak cathodic peak at 1.68 V was associated with the insertion of Na+ into the interlayer of SnS2. Another intense reduction peak at 0.41 V was


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consistent with the conversion reaction of SnS2 and MoS2, the alloying process of Sn. The solid electrolyte interface layer was also generated at this process. After the first cycle, two reduction peaks at around 0.53 V and 0.87 V replaced. The unobvious oxidation peak at 0.41 V was related to the dealloying process of NaxSn. The anodic peaks at 1.26 V and 1.56 V were relevant to the reversible reactions to form SnSx and MoSx.33-35 A good overlap of the discharge/charge profiles after the second cycle was observed in Figure 7A, showing the remarkable electrochemical reversibility. MoS2/SnS2-GS (Figure 7B) reflected an ultrastable sodium storage ability with a reversible capacity of 655 mA h g-1 at 0.15 A g-1 for 100 cycles. At higher current density of 0.75 and 1.5 A g-1 (being activated at 0.15 A g-1 for the initial several cycles), 612 and 546 mA h g-1 can be maintained till 150 cycles, respectively as present in Figure 7C. The rate ability of MoS2/SnS2-GS was indicated in Figure 7D. The specific capacity was 680, 630, 600, 550, 435, 340 mA h g-1 when the current density varied from 0.15, 0.38, 0.75, 1.5, 3.8, to 6.0 A g-1, respectively. The capacity of 685 mA h g-1 was restored when the current density abruptly switched back to 0.15 A g-1, implying the structure robustness of the hybrid. The performance of the as-prepared MoS2/SnS2-GS could be comparable to those reported anode materials for NIBs, as shown in Figure S6. The hybrid electrode after 185 cycles was examined by TEM and STEM-EDX elemental mappings to study the structural variation. As shown Figure 8, the structure can be maintained well and the elemental maps of Sn, Mo, S, and C perfectly overlaid with each other suggesting the structure of MoS2/SnS2-GS was still intact after long cycles. Clearly, the firm immobilization of MoS2 and SnS2 on GS in the hybrid structure is beneficial for boosting the mechanical strength of electrode materials, further contributing to the superior lithium and sodium storage ability. Specifically, the presence of small and uniform binary LMD nanoparticles on the


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graphene sheets, which made double LMD nanoparticles electrochemically active since the electrons could be easily and rapidly transported to LMD nanoparticles via the highly conducting graphene and the lithium/sodium ions could effectively diffuse to binary LMD nanoparticles through pores formed between graphene sheets and binary LMD nanoparticles. More importantly, the perfect confinement of the mixed active materials and asynchronous electrochemical reaction of binary LMDs could effectively buffer volume variation of binary LMDs each other during cycling and ensure the structural integrity, thus mitigating the pulverization problem and strengthening the cycling stability.

CONCLUSION In summary, through a facile one-pot hydrothermal route, binary layered metal dichalcogenides, i.e. SnS2 and MoS2, uniformly grew on GS without any additives to modify the GO surface. With the aid of Sn4+, the charge incompatibility between MoO42- and GO was effectively compromised. The perfect confinement of the mixed active materials on GS and their asynchronous electrochemical reactions favored an outstanding energy storage ability. For LIBs, the reversible capacity of MoS2/SnS2-GS was as high as 1244 mA h g-1 at 150 mA g-1 till 190 cycles. Moreover, at 0.75 A g-1 for 200 cycles, MoS2/SnS2-GS maintained 772 mA h g-1 which was much superior to MoS2-GS and SnS2-GS. For NIBs, MoS2/SnS2-GS also displayed an excellent performance with reversible capacity of 655 mA h g-1, 612 mA h g-1 and 546 mA h g-1 at 0.15 mA g-1, 0.75 A g-1 and 1.5 A g-1 after long cycling accompanied with wonderful rate capability. Via the ingenious strategy whereby inorganic ions, Sn4+, played dual role of mediator to introduce MoO42- and precursor as another SnS2, the conductive carbon matrix was integrated with the poorly conductive LMDs. The method could be explored to prepare a wealth of


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multicomponent hybrid materials which have potential applications in batteries, catalysis, and so forth.

ASSOCIATED CONTENT Supporting information Additional SEM images, TEM images, XRD patterns, ICP-AES results, Raman spectra, XPS spectra of the samples. AUTHOR INFORMATION Corresponding Author *Email: [email protected]; [email protected] Notes The authors declare no competing financial interest. ACKNOWLEDGMENT The authors gratefully acknowledge the financial supports provided by the National Natural Science Fund of China (No. 21601108, 21371108), the Fundamental Research Funds of Shandong University (No. 2016JC033, 2016GN010) and the Taishan Scholar Project of Shandong Province (No. ts201511004). REFERENCES (1) Bruce, P. G.; Freunberger, S. A.; Hardwich, L. J.; Tarascon, J.-M. Li-O2 and Li-S Batteries with High Energy Storage. Nat. Mater., 2012, 11, 19–29.


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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


(2) Chen, Y. M.; Yu, X. Y.; Li, Z.; Paik, U.; Lou, X. W. Hierarchical MoS2 Tubular Structures Internally Wired by Carbon Nanotubes as a Highly Stable Anode Material for Lithium-Ion Batteries. Sci. Adv., 2016, 2, e1600021. (3) Hu, Z.; Wang, L. X.; Zhang, K.; Wang, J. B.; Cheng, F. Y.; Tao, Z. L.; Chen, J. MoS2 Nanoflowers with Expanded Interlayers as High-Performance Anodes for Sodium-Ion Batteries. Angew. Chem. Int. Ed., 2014, 126, 13008–13012. (4) Jiang, Y.; Wei, M.; Feng, J. K.; Ma, Y. C.; Xiong, S. L. Enhancing the Cycling Stability of Na-ion Batteries by Bonding SnS2 Ultrafine Nanocrystals on Amino-Functionalized Graphene Hybrid Nanosheets. Energy Environ. Sci., 2016, 9, 1430–1438. (5) Mei, L.; Xu, C.; Yang, T.; Ma, J.; Chen, L.; Li, Q.; Wang, T. H. Superior Electrochemical Performance of Ultrasmall SnS2 Nanocrystals Decorated on Flexible RGO in Lithium-Ion Batteries. J. Mater. Chem. A, 2013, 1, 8658–8664. (6) Jiang, X.; Yang, X. L.; Zhu, Y. H.; Shen, J. H.; Fan, K. C.; Li, C. Z. In Situ Assembly of Graphene Sheets-Supported SnS2 Nanoplates into 3D Macroporous Aerogels for HighPerformance Lithium Ion Batteries. J. Power Sources, 2013, 237, 178–186. (7) Zhu, C. B.; Mu, X. K.; Aken, P.; Yu, Y.; Maier, J. Single-Layered Ultrasmall Nanoplates of MoS2 Embedded in Carbon Nanofibers with Excellent Electrochemical Performance for Lithium and Sodium Storage. Angew. Chem. Int. Ed., 2014, 53, 2152–2156. (8) Liu, Y. C.; Zhang, N.; Kang, H.; Shang, M.; Jiao, L.; Chen, J. WS2 Nanowires as a HighPerformance Anode for Sodium-Ion Batteries. Chem. Eur. J., 2015, 21, 11878–11884. (9) Xie, X. Q.; Ao, Z.; Su, D.; Zhang, J.; Wang, G. MoS2/Graphene Composite Anodes with Enhanced Performance for Sodium-Ion Batteries: the Role of the Two-Dimensional Heterointerface. Adv. Funct. Mater., 2015, 25, 1393–1403.


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(10) Zhou, F.; Xin, S.; Liang, H.-W.; Song, L.-T.; Yu, S.-H. Carbon Nanofibers Decorated with Molybdenum Disulfide Nanosheets: Synergistic Lithium Storage and Enhanced Electrochemical Performance. Angew. Chem. Int. Ed., 2014, 53, 11552–11556. (11) Zhang, Y. D.; Zhu, P.; Huang, L.; Xie, J.; Zhang, S.; Cao, G.; Zhao, X. B. Few-Layered SnS2 on Few-Layered Reduced Graphene Oxide as Na-Ion Battery Anode with Ultralong Cycle Life and Superior Rate Capability. Adv. Funct. Mater., 2015, 25, 481–489. (12) Qu, B. H.; Ma, C.; Ji, G.; Xu, C.; Xu, J.; Meny, Y.; Wang, T. H.; Lee, J. Y. Layered SnS2Reduced Graphene Oxide Composite-a High-Capacity, High-Rate, and Long-Cycle Life Sodium-Ion Battery Anode Material. Adv. Mater., 2014, 26, 3854–3859. (13) Zhou, T. F.; Pang, W.; Zhang, C.; Yang, J.; Chen, Z.; Liu, H.; Guo, Z. P. Enhanced Sodium-Ion Battery Performance by Structural Phase Transition from Two-Dimensional Hexagonal-SnS2 to Orthorhombic-SnS. ACS Nano, 2014, 8, 8323–8333. (14) Wang, Z.; Chen, T.; Chen, W.; Chang, K.; Ma, L.; Huang, G.; Chen, D.; Lee, J. Y. CTAB-Assisted Synthesis of Single-Layer MoS2-Graphene Composites as Anode Materials of Li-Ion Batteries. J. Mater. Chem. A, 2013, 1, 2202–2210. (15) Jiang, H.; Ren, D. Y.; Wang, H. F.; Hu, Y. J.; Guo, S.; Yuan, H.; Hu, P.; Zhang, L.; Li, C. Z. 2D Monolayer MoS2-Carbon Interoverlapped Superstructure: Engineering Ideal Atomic Interface for Lithium Ion Storage. Adv. Mater., 2015, 27, 3687–3695. (16) Chen, D. Y.; Ji, G.; Ding, B.; Ma, Y.; Qu, B.; Chen, W.; Lee, J. Y. Double TransitionMetal Chalcogenide as a High-Performance Lithium-Ion Battery Anode Material. Ind. Eng. Chem. Res., 2014, 53, 17901–17908.


18

Page 19 of 30

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


(17) Teng, Y.; Zhao, H.; Zhang, Z.; Li, Z.; Xia, Q.; Zhang, Y.; Zhao, L.; Du, X.; Du, Z.; Lv, P.; Swierczek, K. MoS2 Nanosheets Vertically Grown on Graphene Sheets for Lithium-Ion Battery Anodes. ACS Nano, 2016, 10, 8526−8535. (18) Zhang, Q. Q.; Li, R.; Zhang, M.; Zhang, B.; Gou, X. L. SnS2/Reduced Graphene Oxide Nanocomposites with Superior Lithium Storage Performance. Electrochim. Acta, 2014, 115, 425–433. (19) Jiang, Z. F.; Wang, C.; Du, G.; Zhong, Y.; Jiang, J. In Situ Synthesis of SnS2@Graphene Nanocomposites for Rechargeable Lithium Batteries. J. Mater. Chem., 2012, 22, 9494–9496. (20) Hummers, W. S.; Offeman, R. E. Preparation of Graphitic Oxide. J. Am. Chem. Soc., 1958, 80, 1339. (21) Li, J. Y.; Hou, Y.; Gao, X.; Guan, D.; Xie, Y.; Chen, J.; Yuan, C. A Three-Dimensionally Interconnected Carbon Nanotube/Layered MoS2 Nanohybrid Network for Lithium Ion Battery Anode with Superior Rate Capacity and Long-Cycle-Life. Nano Energy, 2015, 16, 10–18. (22) Qin, S.; Lei, W.; Liu, D.; Chen, Y. Advanced N-Doped Mesoporous Molybdenum Disulﬁde Nanosheets and the Enhanced Lithium-Ion Storage Performance. J. Mater. Chem. A, 2016, 4, 1440–1445. (23) Zhao, Y.; Xie, X.; Zhang, J.; Liu, H.; Ahn, H.-J.; Sun, K.; Wang, G. X. MoS2 Nanosheets Supported on 3D Graphene Aerogel as a Highly Efficient Catalyst for Hydrogen Evolution. Chem. Eur. J., 2015, 21, 15908–15913. (24) Hu, H.; Zhao, Z.; Wan, W.; Gogotsi, Y.; Qiu, J. S. Ultralight and Highly Compressible Graphene Aerogels. Adv. Mater., 2013, 25, 2219–2223. (25) Zhou, X.; Wan, L.-J.; Guo, Y.-G. Synthesis of MoS2 Nanosheet/Graphene Nanosheet Hybrid Materials for Stable Lithium Storage. Chem. Commun., 2013, 49, 1838–1840.


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Page 20 of 30

(26) Yang, L.; Wang, S.; Mao, J.; Deng, J.; Gao, Q.; Tang, Y.; Schmidt, O. G. Hierarchical MoS2/Polyaniline Nanowires with Excellent Electrochemical Performance for Lithium-Ion Batteries. Adv. Mater., 2013, 25, 1180–1184. (27) Tang, Y.; Wu, D.; Mai, Y.; Pan, H.; Cao, J.; Yang, C.; Zhang, F.; Feng, X. A TwoDimensional Hybrid with Molybdenum Disulfide Nanocrystals Strongly Coupled on NitrogenEnriched Graphene via Mild Temperature Pyrolysis for High Performance Lithium Storage. Nanoscale, 2014, 6, 14679–14685. (28) Jiang, Y. Feng, Y. Z.; Xi, B. J.; Kai, S. S.; Mi, K.; Feng, J. K.; Zhang, J. H.; Xiong, S. L. Ultrasmall SnS2 Nanoparticles Anchored on Well-Distributed Nitrogen-Doped Graphene Sheets for Li-Ion and Na-Ion Batteries. J. Mater. Chem. A, 2013, 1, 1117–1122. (29) Kim, T.-J.; Kim, C.; Son, D.; Choi, M.; Park, B. Novel SnS2-Nanosheet Anodes for Lithium-Ion Batteries. J. Power Sources, 2007, 167, 529–535. (30) Liu, J.; Wen, Y. R.; Aken, P. A. van; Maier, J.; Yu, Y. In Situ Reduction and Coating of SnS2 Nanobelts for Free-Standing SnS@Polypyrrole-Nanobelt/Carbon Nanotube Paper Electrodes with Superior Li-Ion Storage. J. Mater. Chem. A, 2015, 3, 5259–5265. (31) Du, Y.; Yin, Z.; Rui, X.; Zeng, Z.; Wu, X.-J.; Liu, J.; Zhu, Y.; Zhu, J.; Huang, X.; Yan, Q.; Zhang, H. A Facile, Relative Green, and Inexpensive Synthetic Approach toward LargeScale Production of SnS2 Nanoplates for High-Performance Lithium-Ion Batteries. Nanoscale, 2013, 5, 1456–1459. (32) Zhou, X.; Wan, L.; Guo, Y. Facile Synthesis of MoS2@CMK-3 Nanocomposite as an Improved Anode Material for Lithium-Ion Batteries. Nanoscale, 2012, 4, 5868–5871.


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Page 21 of 30

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(33) Sun, W.; Rui, X.; Yang, D.; Sun, Z.; Li, B.; Zhang, W.; Zong, Y.; Madhavi, S.; Dou, S.; Yan Q. Two-Dimensional Tin Disulfide Nanosheets for Enhanced Sodium Storage. ACS Nano, 2015, 9, 11371-11381. (34) Tu, F.; Xu, X.; Wang, P.; Si, L.; Zhou, X.; Bao, J. A Few-Layer SnS2/Reduced Graphene Oxide Sandwich Hybrid for Efficient Sodium Storage. J. Phys. Chem. C, 2017, 121, 3261−3269. (35) Choi, S. H.; Kang, Y. C. Synergetic Effect of Yolk−Shell Structure and Uniform Mixing of SnS−MoS2 Nanocrystals for Improved Na-ion Storage Capabilities. ACS Appl. Mater. Interfaces, 2015, 7, 24694−24702.


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Figures and captions:

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Figure 1. Schematic illustration of the formation of MoS2/SnS2-GS hybrid. (i) Sn4+ ions were first adsorbed on GO sheets. (ii) MoO42- ions were then adsorbed on GO-Sn4+. (iii) GO-Sn4+MoO42- was transformed into MoS2/SnS2-Graphene hybrids through one-pot hydrothermal process.


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A

B

C

D RGO

E

Mo

Sn F

S

C

Figure 2. Structure and composition study of MoS2/SnS2-GS hybrid. (A,B) SEM images. (C) TEM image (the inset is the corresponding SAED pattern). (D) HRTEM image. (E) STEM-EDX elemental mapping of MoS2/SnS2-GS hybrid showing clearly the homogeneous distribution of


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Sn (purple), Mo (red), S (yellow), and C (green). (F) XRD patterns. Scale bars: 500 nm (A); 200 nm (B); 0.2 µm (C); 5 nm (D); 250 nm (E).

A

B

C

D

Figure 3. XPS spectra of MoS2/SnS2-GS composites: (A) survey spectrum, (B) Sn 3d, (C) Mo 3d, (D) C 1s.


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Figure 4. Characterization of MoS2/SnS2-GS hybrid. (A) HRTEM image of MoS2/SnS2-GS. (B) XRD patterns of S-1, S-2, and S-3. (C) HRTEM image of S-2. (D) Raman spectra of MoS2/SnS2GS, MoS2-GS, SnS2-GS and GO. Scale bars: 5 nm (A&C).


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A

B

C

D

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Figure 5. Electrochemical evalution of MoS2/SnS2-GS electrode for LIBs: (A) discharge-charge voltage curves at 0.15 A g-1; (B) cycling performance at a current density of 0.15 A g-1; (C) cycling performance at a current density of 0.75 A g-1; (D) rate capability at different current densities.


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A

B

C

D

E

F

Figure 6. CV curves of the electrodes made from MoS2-GS (A), SnS2-GS (C), and MoS2/SnS2GS (E) at a scan rate of 0.1 mV s-1 in the voltage range of 0.01–3.00 V versus Li+/Li. Dischargecharge profiles for MoS2-GS (B), SnS2-GS (D), and MoS2/SnS2-GS (F) at a current density of 150 mA g-1.


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A

B

C

D

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Figure 7. Electrochemical evaluation of MoS2/SnS2-GS electrode for NIBs: (A) dischargecharge voltage curves at 0.15 A g-1; (B) cycling performance at a current density of 0.15 A g-1; (C) cycling performance at current densities of 0.75 and 1.5 A g-1, respectively; (D) rate capability at different current densities.


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A

B

C

D

E

F

G

Figure 8. Structure and composition study of MoS2/SnS2-GS hybrid electrode after 185 charge/discharge cycles. (A) TEM image. (B) STEM image. (C-F) STEM-EDX elemental mappings: (C) C, (D) Sn, (E) Mo, and (F) S. (G) The merge image of B, C, D, E, and F. Scale bars: 50 nm (A), 500 nm (B-F).


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TABLE OF CONTENTS

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SnS2 Nanoparticles on Graphene

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