Tin Disulfide Nanosheets with Active Site Enriched Surface

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Energy, Environmental, and Catalysis Applications

Tin Disulfide Nanosheets with Active Site Enriched Surface Interfacially Bonded on rGO Sheets as UltraRobust Anode for Lithium and Sodium Storage Zijia Zhang, Hailei Zhao, Jiejun Fang, Xiwang Chang, Zhaolin Li, and Lina Zhao ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b07741 • Publication Date (Web): 03 Aug 2018 Downloaded from http://pubs.acs.org on August 4, 2018

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ACS Applied Materials & Interfaces

Tin Disulfide Nanosheets with Active Site Enriched Surface Interfacially Bonded on rGO Sheets as Ultra-Robust Anode for Lithium and Sodium Storage Zijia Zhang1, Hailei Zhao1,2,*, Jiejun Fang1, Xiwang Chang3, Zhaolin Li1, Lina Zhao1 1

School of Materials Science and Engineering, University of Science and Technology Beijing,

Beijing 100083, China 2

Beijing Key Lab of New Energy Materials and Technology, Beijing 100083, China

3

State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing,

Beijing 100083, China KEYWORDS: Tin disulfide, graphene, interlinked bond, anode, lithium and sodium ion batteries.

ABSTRACT: Two-dimensional (2D) tin disulfide (SnS2) has attracted intensive research owing to its high specific capacity for Li and Na storage, natural abundance as well as environmental friendliness. However, the poor reaction kinetics, low intrinsic electrical conductivity and severe volumetric variation upon cycling processes impede its widespread application. In this work,

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SnS2 nanosheets with active site enriched surface intimately grown on reduced graphene oxide (rGO) via C-O-Sn chemical bonds are prepared. The aligning affords more active sites for electrode reaction and short transport pathways for Li+/Na+ and electrons. The strong chemical bonding enhances the interfacial affinity of SnS2 with rGO and inhibits the detachment of active SnS2 from rGO during repeated charge and discharge processes, which can ensure an integrated electrode structure. The 3D conductive and flexible rGO network improves the conductivity of the entire composite and buffers the volume change of SnS2 upon charge/discharge. These advantages enable the designed SnS2/rGO nanocomposite to have high specific capacity, superior rate capability and outstanding long-cycling stability for both Li and Na storage.

1. INTRODUCTION The increased use of portable smart devices and electric vehicles along with increasing energy demands have stimulated much research on high-performance energy storage systems. Among them, rechargeable lithium-ion batteries (LIBs) have attracted intense attention due to their high energy density and long-cycling life.1-5 In addition, considerable efforts has been dedicated to research alternative sodium-ion batteries (SIBs) in view of the natural abundance and low cost of sodium resources.6-8 Driven by the surging demands for energy storage applications, the development of high performance LIBs and SIBs is crucially desired. However, commercially used graphite in LIBs has relatively limited specific capacity (372 mAh g-1) for lithium-ion storage and exhibits sluggish reaction kinetics toward sodium-ion storage,9 thus cannot fulfill the increasing demands for new promising rechargeable batteries, which have high energy storage density and power density. Hence, exploring alternative anode materials with high reversible


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capacity, stable cycling performance as well as superior rate capability is critical for both LIBs and SIBs. SnS2, a representative laminar material, has received growing interests as a potential LIBs and SIBs anode material because of its high lithium and sodium storage capacities, natural abundance and eco-friendliness.10,11 Despite these advantages, the practical application of SnS2 anodes is still handicapped by the poor cycling stability, due to the large volume fluctuation during Liion/Na-ion uptake/release process, which results in electrode fracture and gradual electrical disconnection among active particles and between electrode film and the current collector.12,13 To address these issues, great efforts toward integrating nanostructured SnS2-based materials with conductive carbonaceous materials have been devoted.14-19 Among them, graphene, has been considered as a versatile matrix for Li- and Na-storage hosts,20-23 owing to its promising features such as large specific surface area,24 good mechanical resilience,25,26 and superior electronic conductivity.27 Graphene, acting as a glue, can prevent the electronic segregation of the bulk active material even upon localized fracture.18,20,21 Recently,

many

studies

were

conducted

on

the

preparation

of

SnS2/graphene

composites.12,14,15,17,21 These materials exhibit enhanced electrochemical performance in comparison with the pristine SnS2. In the reported works, however, the assembly between nanoSnS2 and graphene sheets is mostly based on poor physical interconnection, which, to some extent, is difficult to keep the electrode integrity because of the weak connection between graphene and active particle when large stress is generated due to volume change of active material during repeated intercalation/deintercalation of Li+ and Na+. In this regard, the design and fabrication of highly durable SnS2-graphene materials with super-stable cycling performance still remains challenging, owing to the lack of rational interface design from molecular level.


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Moreover, from the perspective of spatial geometry, controlling growth orientation of layers of SnS2 versus basal plane of graphene can result in the construction of various nanostructures. Parallel growth of SnS2 layers on graphene can form sheet-on-sheet composites with less active sites, while vertical growth can get SnS2 crystals with more active site exposure (edge side, (hk0) plane), which is beneficial for lithium and sodium ions reactions. Herein, a one-step method for the synthesis of a unique 2D/2D lamellar hybrid structure built from active site enriched SnS2 nanosheets closely anchored on the surface of graphene sheets through strong C-O-Sn bond is reported. The chemical coupling between SnS2 and rGO can prevent the detachment of SnS2 active particle from graphene sheet upon charge/discharge, and therefore enhance the cycling stability of the hybrid SnS2/graphene electrode, especially for SIB with large size Na+ reaction. The aligning of SnS2 nanosheets on rGO sheets can afford sufficient active sites for lithium and sodium ions reaction, while the chemical bonding between SnS2 and rGO can provide fast conductive pathways for the electronic transport, accelerating the electrochemical reaction kinetics. As a result, a durable SnS2/rGO electrode with high capacities, stable cycling performance and superior rate capability for Li+ and Na+ storage can be expected. The prepared SnS2/rGO nanosheets deliver high specific capacities of 1010 and 575 mAh g-1 at 0.1 A g-1 and excellent rate capability of 670 and 320 mAh g-1 at a high current density of 10 A g-1 for LIBs and SIBs, respectively. More attractively, the composite presents superstable cycling performance at 1 A g-1 for over 1000 cycles with reversible capacities close to 910 mAh g-1 and 480 mAh g-1 for LIBs and SIBs, respectively, without detectable capacity degradation. 2. EXPERIMENTAL SECTION 2.1 Materials Synthesis


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The SnS2/rGO nanosheets were prepared via a one-step hydrothermal method. Typically, GO suspension in deionized water was first prepared from natural graphite by the modified Hummers’ method.29 The as-synthesized GO suspension (8 mL) was then diluted by 52 mL deionized water. Afterwards, 0.176 g SnCl4·5H2O was added, followed by the addition of 0.023 g carboxymethyl cellulose (CMC) and 0.226 g thioacetamide (TAA). The mixture was then added into a 100 ml Teflon-lined stainless steel autoclave. The autoclave was heated in an oven up to 180 °C. During the hydrothermal treatment, the initial GO sheets are reduced to rGO via protonation of the surface oxygen functional groups by H+ from water and the followed condensation and dehydration of these functional groups. After reacting for 12 h , the autoclave cooled down naturally until 25 °C. The powders were collected after washing with deionized water and ethanol for several times, and drying overnight in air. For comparison, pure SnS2 nanosheets were prepared under the same condition, but without the addition of CMC and GO suspension. 2.2 Structural Characterization The crystallographic phase of the as-prepared powder was determined by X-ray diffraction (XRD) (Rigaku D/max-A X-ray diffractometer, Cu Kα, Japan). The structure was measured by a LabRAM HR Evolution Raman spectroscope with a 523 nm laser (France). Field emission scanning electron microscopy (FE-SEM) (SUPRA55, Germany) was used to reveal the morphology of the samples. A Tecnai F20 transmission electron microscopy (TEM) (USA) outfitted with scanning TEM (STEM) and high resolution TEM (HR-TEM) measurement was further conducted to investigate the crystal structure. An ESCALAB 250Xi X-ray photoelectron spectrometer (Thermo Fisher, USA) was used to record X-ray photoelectron spectra (XPS). Fourier transform infrared spectroscopy (FT-IR) was obtained using a Bruker TENSOR 27


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spectrometer (Thermo Fisher Scientific, USA). The tested samples were prepared through the KBr pellet method. A NETZSCH STA 449C thermogravimetric/differential thermal analysis (TG/DTA) thermal analyzer (Germany) was used to estimate the carbon content of the samples under air atmosphere in the temperature range of room temperature to 700 °C at a heating rate of 10 °C min-1. The electrical conductivity was measured at ambient temperature using a twoelectrode method with a digital multimeter (BM857, China). Before the measurement, the sample was compressed into a disc with a diameter of 10 mm under a pressure of 10 MPa. Solidstate magic angle spinning nuclear magnetic resonance (MAS-NMR) measurements were performed at 1 MHz on a Bruker AVWB III600 spectrometer using a 4 mm MAS probe a rotor spinning speed of 12 kHz. In order to study the electron properties, the calculations were conducted via the plane-wave pseudopotential method within density functional theory (DFT) in CASTEP code.30 We used the generalized gradient approximation (GGA) in Perdew-Burke-Ernzerhof (PBE) format to describe the ground state structure.31 SnS2 with a 5 × 2 supercell deposited on (4 × 6) graphene was employed for calculating the density of states (DOS). The energy cut-off was set at 340 eV. The Broy-den-Fletcher-Goldfarb-Shanno (BFGS) method with stress, convergence of energy change per atom and residual force less than 0.05 GPa, 1 × 10-6 eV and 0.03 Å-1, respectively, was used to conduct the geometry optimization. . 2.3 Electrochemical Li-/Na-ion Storage Performance To prepare the working electrodes, 80 wt. % active material was blended with10 wt. % acetylene black and 10 wt. % CMC and uniformly dispersed in water. Then the slurry was homogeneously blade-coated onto copper foil, vacuum dried at 70 °C and cut into 8 mm circular


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pellets. Prior to cell assemble, the electrodes were further vacuum-dried overnight at 120 °C. We used Celgard 2400 as the separator and lithium foil as the counter electrode. The electrolyte was 1 M LiPF6 in a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) (1:1:1, in vol %). For SIBs, glass microfibers of Whatman GF/F was employed as the separator, sodium foil as the counter electrode, and 1.0 M NaClO4 in mixed EC and DMC (volume ratio, 1:1) as the electrolyte. Galvanostatic cycling tests were conducted in the voltage range from 0.01 to 2.5 V on a multichannel battery testing instrument (LAND CT-2001A, China). Electrochemical impedance spectra (EIS) in the 0.1-106 Hz frequency range were collected by a Solartron 1260A frequency response analyzer (United Kingdom).


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3. RESULTS AND DISCUSSION

Figure 1. XRD patterns of SnS2/rGO nanosheets and pure SnS2 (a); structural illustrations of SnS2 with terminated (001) and (100) planes (b). XRD patterns of pure SnS2 and SnS2/rGO nanosheets are displayed in Figure 1a. The pristine SnS2 material exhibits a typical hexagonal structure, which is in accordance with hexagonal SnS2. The SnS2/rGO composite basically retains the position of the diffraction peaks of SnS2. However, the intensity of the (001) plane is the strongest for pure SnS2, while a predominant peak of (100) plane is observed for SnS2/rGO, suggesting the different crystal orientations of SnS2 in the two samples. SnS2 has a layered structure, as shown in Figure 1b. The crystallographic feature of SnS2 makes it tend to form 2D materials with (001) plane exposed. Apparently, the incorperation of GO suppresses the growth of (001) plane but promotes the development of Sn atom exposed plane (i.e., (100) plane). A small diffraction peak detected at 2θ = 26o of SnS2/rGO composite indicates the existence of rGO in the composite.32,33 The Raman


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result further verifies the presence of rGO component (Supporting Information (SI), Figure S1). The Raman peaks at 1332, 1602, 2684, and 2907 cm-1 can be assigned to the D, G, 2D, and D+G bands of graphene sheets,34-37 respectively.


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Figure 2. FE-SEM (a), TEM (b, c) and HR-TEM (d) images of SnS2/rGO composite; the inset of (d) is the enlarged image of the selected area marked by a rectangle. (e) STEM image and corresponding Sn (pink), S (green) and C (red) elements mapping images of. The morphology of the products SnS2 and SnS2/rGO was characterized by FE-SEM and TEM. The SnS2 sample displays typical nanosheet structure (Figure S2). While, the SnS2/rGO


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composite shows a rippled sheet-like morphology. These SnS2/rGO nanosheets assemble together to form a much porous structure (215.6 m2 g-1), which, with submicro-sized pores (Figure 2a), is beneficial for the penetration of electrolyte solution and thus can increase the contact between active particles and electrolyte and facilitate the electrode reaction kinetics. With high magnification (Figure 2b), some thin strips (dark color) interweaved with semitransparent rGO are observed, which show the average width and length of ~20 nm and ~150 nm, respectively (Figure 2c). The scrutinization by HR-TEM reveals the well defined crystal feature of the thin strips, which show clear lattice fringes of 0.571 nm, consistent with the interplanar distance of (001) planes in hexagonal SnS2 crystal (Figure 2d).16,23 This result indicates that these nanosheets are SnS2 crystals, which grow vertically on rGO sheets. This means that the SnS2 sheets align with their c-axis (i.e., [001] direction) parallel to rGO sheet. The result accords well with the restrained growth of (001) plane of SnS2 nanosheets (Figure 1). Moreover, amorphous rGO substrate denoted by the arrow can be distinctly observed. STEM and elemental mapping analysis of SnS2/rGO (Figure 2e) for Sn, S and C demonstrates the homogeneous distribution of chemical composition and high structure affinity between rGO sheets and SnS2 nanosheets.

Figure 3. Schematic illustration for synthesis procedure of SnS2/rGO composite.


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The synthesis process is depicted in Figure 3. The pristine GO sheet is negatively charged in suspension, as revealed in Figure S3 in SI. With addition of SnCl4, the hydrolysis of Sn4+ occurs, resulting in the formation of strong acid atmosphere (pH≈1), which gives rise to positively charged GO (SI, Figure S3).38,39 Then the hydrolyzed Sn(OH)4 couples with GO through the dehydration reaction to form C-O-Sn bonds. TAA provides S ions to generate subsequently SnS2 nanocrystals on the GO substrate. The formation of C-O-Sn bond will induce the Sn atom plane to grow parallel to GO sheet, which is the edge side of layered SnS2 nanocrystals (i.e., (100) plane). Then, the layer structured SnS2 crystals vertically grown on rGO substrate via C-O-Sn bonds is formed. CMC long-chain molecule functions as a block to prevent the SnS2 nanocrystals from aggregation during growth. The content of rGO in the SnS2/rGO composite was determined by TGA measurement (SI, Figure S4). After heat treatment in air, the remained phase is assumed to be SnO2, the content of rGO in the SnS2/rGO composite is about 13 wt.%.


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Figure 4. XPS spectra of SnS2/rGO: (a) survey spectrum; (b) C 1s; (c) O 1s; (d) Sn 3d; (e) S 2p. The binding feature between the rGO and SnS2 was studied by XPS. Figure 4a reveals the existence of C, O, Sn and S elements in the SnS2/rGO composite. The three single peaks at 284.8, 285.9 and 288.7 eV in C 1s spectrum (Figure 4b) are assigned to nonoxygenated carbon (C-C/C=C),38,40 C-OH/C-O-Sn groups,38,40 and O-C=O groups,41,42 respectively. In the O 1s spectrum (Figure 4c), the peaks at 531.1 eV and 533.4 eV are attributed to C=O groups,41,42 and C-OH and/or C-O-C groups,41,42 respectively. The new peak located at 532.0 eV corresponds to the formation of C-O-Sn bond.38,40,43,44 Characteristic peaks of Sn 3d and S 2p are observed at 487.3 and 495.7 eV, and 162.1 and 163.3 eV (Figure 4d,e),16 respectively, which slightly shift to a higher energy (by 0.5 eV, SI, Table S1) compared to that of SnS2 (SI, Figure S5), suggesting a decreased density of electron clouds around Sn ions in SnS2/rGO composite. This shift is


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ascribed to the higher electronegativity of oxygen (3.44) than that of sulfur (2.58) on the Pauling scale and demonstrates the formation of C-O-Sn bond, as described in Figure 3.

Figure 5. (a) 13C MAS-NMR spectra of pure GO and SnS2/rGO. (b) FT-IR spectra of pristine SnS2 and SnS2/rGO composite. Solid-state 13C MAS-NMR measurement provides additional evidence for the formation of CO-Sn bond. As shown in Figure 5a, for pure GO, the peaks around 61 ppm, 70 ppm and 133 ppm originate from the carbon atoms bonding to the epoxy group, hydroxyl group connected to the carbon atoms, and graphitic sp2 carbon,34,45 respectively. In addition, the weak peaks located at 99, 166, and 191 ppm are ascribed to the lactol, ester carbonyl, and ketone groups, respectively.45 While, for SnS2/rGO, the peaks with chemical shift of 61 and 70 ppm completely disappear, suggesting nearly complete reduction of GO sheets. The peak corresponding to graphitic sp2 shows a significant downfield shift compared with that of GO, indicating an enhanced electron density around 13C nuclei, which is due to the generation of C-O-Sn bond and the elimination of C-OH bond. The lower electro-negativity of Sn than that of H renders more electrons around


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carbon atoms. An emerging shoulder peak in the spectrum of SnS2/rGO located at 140 ppm should be assigned to the C-O-Sn bonds.46 The C-O-Sn coupling between rGO and SnS2 was further corroborated by FT-IR result (Figure 5b). The SnS2/rGO sample presents more intense adsorption at 1113 cm-1 comparing with pure SnS2, which is associated with the presence of C-O-Sn bond.40 Additionally, the emerging peak at 621 cm-1 in the spectrum of SnS2/rGO is assignable to the Sn-O bond.47

Figure 6. (a) First principle calculations models of SnS2 bonded with graphene. (b) Calculated band structure and (c) DOS of SnS2/graphene model. To study the electron properties, the band structures as well as DOS are calculated based on the optimized structure of SnS2/rGO (Figure 6a), pure SnS2 (SI, Figure S6a) and rGO (SI, Figure


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S6b). The results show that the band gap of pure SnS2 is 2.52 eV (SI, Figure S6c), which is consistent with other reported values.48,49 While pure rGO (SI, Figure S6d) and SnS2/rGO (Figure 6b) show metallic electronic structure as the Fermi level are at the bottom of the conduction band. As a consequence, the considered SnS2/rGO should have excellent conductivity. The DOS curves presented in Figure 6c indicate that the p states of C and S atoms mainly contribute to the metallic behavior of SnS2/rGO. To further strengthen the result, electrical conductivity measurements of the samples are conducted. The results (SI, Table S2) show SnS2/rGO exhibits much higher electrical conductivity than that of pure SnS2. Moreover, it is higher than that of physically mixed SnS2 and rGO, and similar with that of pure rGO. This result indicates that the intimate coupling between SnS2 and rGO via C-O-Sn bond affords efficient electronic conducting pathway inside the composite material. Galvanostatic charge/discharge in the voltage range of 0.01 and 2.5 V, the SnS2/rGO electrode delivers initial lithiation and delithiation capacities of 1450 mAh g-1 and 1020 mAh g-1 at 0.1 A g-1 (SI, Figure S7a). The related Columbic efficiency (CE) is 70%. This irreversible capacity loss could be attributed to electrolyte decomposition and solid electrolyte interface (SEI) formation.20,21 The charge/discharge profiles for Na-ion storage are similar to the curves for Liion storage, only with lower voltage and capacity, which is due to the difference in the thermodynamics and kinetics for the Li and Na ions uptake. As indicated in Figure S7b in SI, the first sodiation and desodiation capacities are 880 mAh g-1 and 600 mAh g-1, corresponding to a CE of 68%. From the 2nd cycle onwards, the voltage profiles of SnS2/rGO for LIBs and SIBs almost overlap with each other, demonstrating high electrochemical reversibility for Li- and Naion storage.


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Figure 7. Cycling performance (a), rate performance (b) and long-cycle capability (c) of SnS2/rGO electrode for lithium storage. The cycling performance of the prepared SnS2/rGO electrode for LIBs was evaluated under the voltage range of 0.01-2.5 V at a current density of 0.1 A g-1 (Figure 7a). The lithiation capacity is 1030 mAh g-1 in the second cycle and maintains 1010 mAh g-1 after 200 cycles, corresponding to a capacity retention of 98 %. CV tests were employed to investigate the contribution of pseudocapacitance to this high reversible capacity. The result (SI, Figure S8) indicates that ~72% of the total capacity of SnS2/rGO is attributed to surface capacitive mechanism. The high surface capacitive feature will endow the electrode with high rate performance. Indeed, a superior rate capability is exhibited with reversible capacities of 900 mAh g-1, 860 mAh g-1 810 mAh g-1 and 740 mAh g-1 at 0.5 A g-1, 1 A g-1, 2 A g-1 and 5 A g-1, respectively (Figure 7b). Even at a high


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rate of 10 A g-1, the specific capacity as high as 670 mAh g-1 can be delivered. When the current rate returns back to 1 A g-1 and 0.1 A g-1, the capacity can be recovered to 880 mAh g-1 and 1015 mAh g-1, respectively, suggesting the excellent robustness of the electrode even at high current rates. For long-term cycling, the SnS2/rGO electrode delivers a high and stable reversible capacity of 910 mAh g-1 at 1 A g-1 over 1000 cycles without distinct capacity degradation (Figure 7c). Taking the SnS2-based materials reported so far for comparison (SI, Table S3), the SnS2/rGO material reported here exhibits high reversible capacity, decent cycling stability and exceptional rate capability as anodes for LIBs.

Figure 8. Cycling performance (a), rate performance (b) and long-cycle capability (c) of SnS2/rGO electrode for sodium storage.


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The Na-storage properties of SnS2/rGO were also evaluated under identical conditions. As displayed in Figure 8a, the specific capacity of the electrode reaches 620 mAh g-1 at the second cycle and stabilizes at 575 mAh g-1 for subsequent 200 cycles at 0.1 A g-1. Figure 8b indicates that the electrode delivers an outstanding rate capability with a reversible capacity of 320 mAh g1

even at a current rate of 10 A g-1. When the current rate is restored to 1 A g-1 and 0.1 A g-1, the

SnS2/rGO electrode can still regain reversible capacities of 475 mAh g-1 and 585 mAh g-1, respectively, approaching to the values in the early cycles. More importantly, the electrode can still deliver a ultra-high specific capacity up to 480 mAh g-1 at a high current rate of 1 A g-1 over 1000 cycles (Figure 8c), with capacity decay rate of only 0.009% from 2th to 1000th cycle. In comparison to other recently reported SnS2-based SIB anodes, the prepared SnS2/rGO material delivers outstanding cycling stability and superior rate capability. In contrast, SnS2 nanosheets without graphene incorporation exhibit poor electrochemical performance for both Li+ and Na+ storages with fast capacity degradation and inferior rate capability (SI, Figure S9,S10).


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Figure 9. Schematic illustration of the enhanced electrochemical performance of SnS2/rGO in the Li-/Na-ion battery system. The super high capacities and stable cycling performance for both Li- and Na-ion storage of sheet-on-sheet heterostructured SnS2/rGO composite can be ascribed to its unique structural features (Figure 9). Firstly, the aligned SnS2 nanosheets supply abundant active site for electrode reaction and short distance for ion diffusion, which guarantee a facilitated electrochemical reaction kinetics. Secondly, the strong bonding between active SnS2 and highly conductive graphene matrix not only affords effective electronic transport systems, but also ensures the structural integrity of the active particle and prevents the nanosheets of SnS2 from aggregation during repeated cycling processes. Thirdly, the mechanical resilience of graphene can buffer the volume change of SnS2 upon cycling and thus reinforce the electrode stability. Forthly, the


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micro-porous structure of the composite provides more passageways for electrolyte solution penetration to increase the contact between electrode and electrolyte and thus enhance the electrode reaction kinetics. The EIS measurement reveals that the SnS2/rGO electrode shows slight variation in electrode impedance in both LIB and SIB after 100 and 400 cycles (SI, Figure S11), demonstrating the robust structure of the electrode. While distinct increase of the impedance can be observed for pure SnS2 electrode (SI, Figure S12). A post-mortem observation of the SnS2/rGO electrode before and after 100 cycles for LIBs and SIBs clearly shows that the integrity of the electrode is well preserved (SI, Figure S13,S14), indicating that the designed SnS2/rGO composite is able to counteract the big volume expansion/contraction during repeated Li- and Na-ion uptake/release processes. While, many obvious cracks can be observed on the surface of SnS2 electrode after both the Li+ and Na+ insertion processes (SI, Figure S15). 4. CONCLUSION In summary, we designed a facile self-assembly strategy to prepare SnS2 nanosheets with active site enriched surface interfacially coupled with rGO sheets through C-O-Sn bond as anode for rechargeable LIBs and SIBs. This designed structure not only ensures rapid Li-ion/Na-ion diffusion and electron transport throughout the entire composite, but also provides a strong structure stability to tolerate the large volume variation during repeated cycling processes. The prepared SnS2/rGO anode exhibits high reversible capacity for both LIBs and SIBs (1010 mAh g1

and 575 mAh g-1 at 0.1 A g-1, respectively), excellent rate capability and superior cycling

stability (95% and 91% capacity retention at 1 A g-1 after 1000 cycles, respectively). These


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results clearly reveal the promising application of this unique heterostructured SnS2/rGO nanosheets as anode material for high performance LIBs and SIBs. ASSOCIATED CONTENT Supporting Information. Raman spectrum of SnS2/rGO nanocomposite, FE-SEM image of SnS2 nanosheets, Zeta potential of pristine GO suspension and GO suspension after adding SnCl4, TG curve of SnS2/rGO composite in air, XPS spectra of pure SnS2, binding energy of Sn 3d and S 2p for pristine SnS2 and SnS2/rGO nanocomposite, structural models for first principle calculations, calculated band gap and DOS of pure SnS2 and graphene, selected charge-discharge voltage profiles of SnS2/rGO electrode for lithium (a) and sodium (b) storage, electrical conductivities of samples SnS2/rGO, pristine SnS2, rGO and physically mixed SnS2 and rGO, cycling performance and rate capability of the structured SnS2 materials reported recently for Liion and Na-ion battery anodes, CV curves and specific peak current of SnS2/rGO at various sweep rates from 0.2 to 1.0 mV s-1, CV curves of SnS2/rGO with separation between total current and surface capacitive current at 0.1 mV s-1, Cycling performance, rate performance and longcycle capability of SnS2 electrode for lithium and sodium storage, Nyquist plots of SnS2/rGO and SnS2 electrodes for lithium and sodium storage in the range of 0.1 Hz to 106 Hz, FE-SEM images of SnS2/rGO and SnS2 electrodes before and after cycling for LIBs and SIBs, TEM image of SnS2/rGO nanosheets after Li+ insertion. This information is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected].


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Table of Contents


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Tin Disulfide Nanosheets with Active Site Enriched Surface

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