(101) Plane-Oriented SnS2 Nanoplates with Carbon Coating: A High

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(101) plane-oriented SnS nanoplates with carbon coating: a highrate and cycle-stable anode material for lithium ion batteries Zijia Zhang, Hailei Zhao, Zhihong Du, Xiwang Chang, Lina Zhao, Xuefei Du, Zhaolin Li, Yongqiang Teng, Jiejun Fang, and Konrad Swierczek ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b11113 • Publication Date (Web): 26 Sep 2017 Downloaded from http://pubs.acs.org on September 29, 2017

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ACS Applied Materials & Interfaces

(101) plane-oriented SnS2 nanoplates with carbon coating: a high-rate and cycle-stable anode material for lithium ion batteries Zijia Zhang1, Hailei Zhao1,2,*, Zhihong Du1, Xiwang Chang1, Lina Zhao1, Xuefei Du1, Zhaolin Li1, Yongqiang Teng1,Jiejun Fang1, Konrad Świerczek3,4 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

AGH University of Science and Technology, Faculty of Energy and Fuels, Department of

Hydrogen Energy, al. A. Mickiewicza 30, 30-059 Krakow, Poland

4

AGH Centre of Energy, AGH University of Science and Technology, ul. Czarnowiejska 36, 30-

054 Krakow, Poland

KEYWORDS: Tin disulfide, oriented growth, carbon coating, anode material, lithium ion battery.

ABSTRACT: Tin disulphide is considered as a promising anode material for Li-ion batteries, because of its high theoretical capacity, as well as natural abundance of sulfur and tin. Practical

ACS Paragon Plus Environment

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implementation of tin disuphide is, however, strongly hindered by inferior rate performance and poor cycling stability of not optimized material. In this work, carbon-encapsulated tin disuphide nanoplates with (101) plane orientation are prepared via a facile hydrothermal method, using polyethylene glycol as a surfactant to guide the crystal growth orientation, followed by a lowtemperature carbon coating process. Fast lithium ion diffusion channels are abundant and wellexposed on the surface of such obtained tin disuphide nanoplates, while the designed microstructure allows to effectively decrease Li-ion diffusion length in the electrode material. In addition, the outer carbon layer enhances the microscopic electrical conductivity and buffers the volumetric changes of the active particles during cycling. The optimized, carbon-coated tin disuphide (101) nanoplates deliver a very high reversible capacity (960 mAh g-1 at a current density of 0.1 A g-1), superior rate capability (796 mAh g-1 at a current density as high as 2 A g1

), and an excellent cycling stability at 0.5 A g-1 for 300 cycles, with only 0.05% capacity decay

per cycle.

1. INTRODUCTION With an imminent shortage of fossil fuels and growing environmental concerns about global warming, renewable energy resources such as solar, wind, hydropower and geothermal energies, offering sustainable energy without sacrificing environmental quality, are expected to be an intensively growing component of the energy market. Those energy resources rely strongly on natural conditions, thus showing intermittent operation features in time and space. In order to maintain grid balance and provide electrical energy safety, large-scale electric energy storage systems are considered indispensable for a smooth integration of these intermittent energies. Rechargeable lithium ion batteries (LIBs) are promising energy storage devices, due to their


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high energy and power density and long cycle life. They have been widely used in electronic products, and now gradually extend the application to electric vehicles, space exploration and distributed energy storage.1-5 Carbon-based compounds are the most commonly used anode materials for commercial LIBs. However, graphite possesses a low theoretical capacity of 372 mAh g-1, and exhibits poor lithium ion insertion/extraction kinetics. It also suffers from safety issues when charging/discharging at high rate and/or low temperature, due to its low lithiation potential close to that of metal lithium deposition.6-10 These downsides make carbon-based anodes difficult to satisfy the increasing demand for high energy and power densities of LIB. Especially, fast charge capability is essential for renewable energies storage considering their instantaneous high power features. Therefore, exploring alternative materials that have high reversible storage capacity, excellent rate capability and long-term stability is of significance to develop next generation LIBs for the emerging new applications. Among the possible candidates, tin disulphide (SnS2), an important inorganic layered material, has drawn considerable attention, due to its high theoretical capacity of 1232 mAh g-1, natural abundance of S and Sn, as well as eco-friendliness.11-13 However, behind the towering merits, unoptimized SnS2 electrodes suffer from inferior rate capability and poor cycling stability, limiting their practical applications in LIBs. These issues are largely ascribed to the low conductivity and severe volumetric expansion/shrinkage during cycling processes,14-16 which could lead to a partial interruption of electronic and ionic diffusion pathways. To overcome those limitations, tailoring the SnS2 particles down to a nano-scale dimension and customizing microstructures to the shape of fullerene-like nanoparticles,17 nanoflakes,18 nanorods,19 nanobelts,20 nanoplates21 and hollow structures,22 as well as compositing with conductive matrices,14,23-25 have been employed and were shown to be effective design strategies. The


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orientation of crystals could also have strong impact on the charge transport and electrochemical properties of electrode materials.26-28 SnS2 possesses a layered structure, in which Sn atoms are sandwiched between two layers of hexagonally arranged and closely-packed S atoms, and the adjacent sandwich blocks are hold together by weak van der Waals forces.21,29,30 Considering the highly anisotropic, 2-dimensional (2D) layered crystal structure of SnS2 and the preferential migration of lithium ion along van der Waals layers (001) (i.e. perpendicular to the c-axis),21,31 to prepare SnS2 crystals with exposure surface having more sites to access the (001) planes is expected to promote the lithium ion diffusion into active material, and thus enhance the electrode reaction kinetics. Actually, the SnS2 crystals preferentially grow along (001) planes, forming platelet-like microstructure with less sites for lithium ion diffusing into SnS2, limiting kinetics of the electrode reaction. For common SnS2 plates with (001) plane exposure, S atoms locate on the outer surface of (001) plane, while on the direction of (101) plane, Sn atoms could be exposed. The (101) plane would provide more sites for lithium ion access into layered SnS2. To guide the formation of tin controlled surface (101), polyethylene glycol (PEG), in which the oxygen atom has strong coordination abilities with cations, was used as crystal growth conditioner in this work. Additionally, combining SnS2 materials with carbon matrix can improve the electrical conductivity and buffer the volume change of SnS2 during lithiation/delithiation process.32-35 With this synthesis design, we successfully prepared carbon encapsulated SnS2 nanoplates with oriented (101) plane by a facile hydrothermal method followed with a low temperature carbon coating process. The as-prepared electrode exhibits high reversible capacity, superior rate capability, as well as excellent cycling stability.


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2. EXPERIMENTAL SECTION 2.1 Preparation of Carbon Encapsulated SnS2 Nanoplates with Oriented (101) Planes The SnS2 nanoplates with dominant (101) facet were synthesized by a facile hydrothermal route with PEG 400 as surfactant. Typically, 0.701 g of SnCl4·5H2O was dissolved in a mixture of 35 mL of deionized water and 20 mL of PEG 400. Then, 0.457 g of thiourea was added into the solution. Subsequently, the mixture was transferred into a 100 mL Teflon-lined stainless steel autoclave, and heated in an oven at 180 °C for 15 h. Finally, the autoclave was cooled down to room temperature naturally. The products were filtered, washed with deionized water/ethanol several times, and dried in air at 60 °C overnight. Then, carbon coating was carried out on the synthesized sample via chemical vapor deposition. Specifically, 0.1 g of (101) oriented SnS2 nanoplates was placed in a quartz tube under a gas flow of acetylene in Ar mixture with 1:3 volumeric ratio, and was heated at 5 °C min-1 up to 375 °C, at which it was kept for 15 mins. For comparison, SnS2 nanoplates with dominant (001) plane were prepared under the same condition, but without the addition of PEG 400. 2.2 Structural Characterization The phase composition and crystal structure of the synthesized products were identified by Xray diffraction (XRD) (Rigaku D/max-AX-ray diffractometer, Cu Kα, λ=1.5406 Å, Japan). X-ray datas were refined by Rietveld method using GSAS/EXPGUI set of software. Due to a plateletlike microstructure, particle size broadening parameters were included in the refinements. In addition, as deduced from a presence of broadened subset of diffraction peaks for sample with (101) orientation, stacking fault model along c-axis was included in the respective refinement. The morphology and atomic-scale lattice structure of the samples were characterized using field


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emission scanning electron microscopy (FE-SEM) (SUPRA55, Germany) and (transmission electron microscopy) (TEM) (Tecnai F20, 200 kV, USA) equipped with high resolution TEM (HR-TEM). X-ray photoelectron spectra (XPS) were measured on Thermofisher Scientific Escalab 250Xi (USA) apparatus with a monochromatic Al Kα radiation (hν =1253.6 eV). The thermogravimetric analysis (TGA) was carried out to precisely estimate the contents of SnS2 and carbon present in the investigated sample by using a TG/DTA thermal analyzer (NETZSCH STA 449C, Germany). Measurements were performed from room temperature to 700 °C at a heating rate of 10 °C min-1 in air. Considering that the periodic model calculation is more reasonable than the aperiodic model calculation, the first-principles calculations were performed using Materials Studio software through the CASTEP package to evaluate the surface energy and total energy. The surface energy calculations were conducted using a slab model with periodic boundary conditions. The surfaces were cleaved from a bulk structure with lattice constants obtained after the optimization. The depths of the surface regions were chosen to be large enough to ensure full relaxation of the surface. The surface energy equals = + − , where is the total energy of a pure unit, and are the total energies for the Sn- and S-terminated slabs, respectively. The total energies of a fully relaxed unit with adsorbed PEG on SnS2 (001) and (101) surfaces were calculated to show which plane PEG prefers to induce during synthesis. 2.3 Electrochemical Measurements The working electrodes for electrochemical tests were prepared by mixing 70 wt. % active material, 15 wt. % acetylene black and 15 wt. % carboxymethylcellulose with water, under magnetic stirring for 24 h. The formed homogeneous slurry was then coated onto copper foil,


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dried at 70 °C for 6 h under vacuum, and punched into disks with a diameter of 8 mm. The loading of the active material in the electrode was ~0.8 mg cm-2. Before cell assembling, the electrodes were further dried at 120 °C for 24 h under vacuum. The 2032 coin-type cells were assembled in an Ar-filled glove box with lithium foil as the counter electrode and Celgard 2400 as the separator. The electrolyte was 1 M LiPF6 dissolved in ethylene carbonate, diethyl carbonate and dimethyl carbonate (1:1:1, in vol. %). Galvanostatic charge/discharge tests were performed in a potential window from 0.01 V to 3.0 V (vs. Li+/Li). Cyclic voltammetry (CV) measurements were carried out at a scanning rate of 0.1-0.5 mV s-1. Electrochemical impedance spectra (EIS) were analyzed at a fully-charged state in the frequency range from 0.1 to 106 Hz, while the disturbance amplitude was 5 mV. 3. RESULTS AND DISCUSSION

Figure 1. XRD pattern with Rietveld refinement of carbon-encapsulated SnS2 nanoplates with oriented (101) plane.


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Figure 1 shows the XRD data with Rietveld refinement of the synthesized sample. As can be seen, all diffraction peaks can be well-indexed as a typical SnS2, which belongs to 2T-type layered structure (JCPDS card: No. 23-0677). Interestingly, the sample exhibits a remarkably strong (101) peak and a relatively weak (001) peak, which is opposite comparing to the standard XRD pattern, while sample synthesized without PEG addition shows normal XRD peak pattern (Figure S1 in the Supporting Information (SI)). This result suggests that the two samples contain grains having different crystal growth orientations, with dominant (101) and (001) planes, respectively. As the two materials were prepared in the same process, but with or without the addition of PEG, it can be concluded that PEG influences exposed facets of SnS2 crystals, while it does not alter the phase development of the final product. Table S1 in SI presents the refined structural parameters for the samples, as well as the calculated average stacking fault separation (along c-axis). Presence of stacking faults in the sample with PEG indicates the imperfection of the grown crystals. Well-developed (001) planes stacked along c-axis are less-prone to have faults in their arrangements.


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Figure 2. FE-SEM micrographs (a, b) of carbon-encapsulated SnS2 nanoplates with oriented (101) plane. Inset of (a) is the image of a desert rose mineral. The morphologies of the prepared samples were observed by FE-SEM. As shown in Figure 2a, well-dispersed microstructure resembling a desert rose-like particle (inset of Figure 2a) can be clearly observed. A magnified micrograph in Figure 2b shows that individual desert rose-like particles are assembled from interleaving SnS2 nanoplates. The estimated average diameter and thickness of the nanoplates are 1-1.5 µm and ~75 nm, respectively. Similar morphology was observed for the sample synthesized without PEG (SI, Figure S2), while the nanoplates there have similar thickness.


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Figure 3. TEM (a) and HR-TEM (b, c) micrographs of carbon-encapsulated SnS2 nanoplates with oriented (101) plane. (d) The crystal structure of SnS2 with (101) plane orientation. TEM and HR-TEM observations were performed to investigate the intrinsic atomic arrangement present in the considered samples. Figure 3a confirms the desert rose-like structure and 2D symmetry feature of the SnS2 nanoplates. The HR-TEM micrograph (Figure 3b) exhibits the lattice structure, which gives the interatomic distances of 0.316 nm, 0.274 nm and 0.279 nm, corresponding to (010), (1-1-1) and (-101) planes with interfacial angles of 116 °, 128 °, and 116 °, respectively. The selected area electron diffraction (SAED) pattern shown in the inset of Figure 3a indicates that crystal growth orientation of the SnS2 nanoplates is prominently along


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(101) plane. A uniform carbon layer with a thickness of 3 nm can be observed on primary (101) facet-dominated SnS2 nanoplates (Figure 3c). While, the SnS2 nanoplates synthesized without PEG mainly grow along (001) plane (SI, Figure S3). On the basis of above discussion, it can be concluded that the TEM and HR-TEM analyses coincide well with the XRD results, confirming that samples prepared with and without PEG during synthesis procedure present different growth orientations with exposed (101) and (001) facets, respectively. Here we can also infer that PEG addition during synthesis is responsible for the distinct crystal orientation. Its ending oxygen atom ensures the inducing growth of crystal with special orientation owing to its preferential coordination with cations. The crystal structures of SnS2 with (101) plane orientation is illustrated in Figure 3d. Apparently, fast lithium ion diffusion and sufficient electrochemical reaction sites are expected for SnS2 plates with (101) facets. XPS studies were also conducted to investigate the chemical state of Sn and S in the synthesized samples with and without PEG addition. As shown in Figure S4,S5 in SI, the two samples present similar spectra, with Sn and S peaks belonging to Sn4+ and S2-, demonstrating that the two samples have similar chemical state of SnS2. The precise contents of SnS2 and carbon present in carbon-coated SnS2 nanoplates with oriented (101) plane are determined by the recorded TGA curve of the sample (SI, Figure S6). Assuming that the remaining product after oxidation during TGA measurement is pure SnO2,11,16 it was derived that the contents of amorphous carbon and SnS2 in the considered sample are 9.3 wt% and 90.7 wt%, respectively.


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Figure 4. Structural models of terminated (101) and (001) surfaces of SnS2 with adsorbed PEG for first-principles calculation. The blue, yellow, green, grey and red balls denote Sn, S, H, C and O atoms, respectively. First-principles calculations were performed using Materials Studio software (CASTEP code) to get insight into the effect of PEG addition on the growth behaviour of the SnS2 nanoplates. The calculated results reveal that the surface energy of (001) facet-terminated SnS2 is reduced by 0.11 eV, compared with that of (101) surface, indicating that SnS2 nanoplates are preferentially exposed with energetically stable (001) surfaces. However, with PEG addition (Figure 4), the exposed surface can be different because of the inducing growth effect of surfactant PEG. The calculation indicates that the total energy of SnS2 with terminated (101) plane connecting with


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PEG is 0.09 eV lower than that with terminated (001) plane, suggesting that PEG is more favourable to induce the growth of (101) facets.

Figure 5. Schematic illustration of the formation process for carbon encapsulated SnS2 nanoplates with oriented (101) plane. To further understand the evolution process of the desert rose-like structure of (101) oriented SnS2 nanoplates, samples prepared at different stages (after 1 h, 3 h, 9 h, and 15 h) of the hydrothermal process were extracted and investigated. The corresponding XRD patterns and FESEM micrographs are given in Figure S7 in SI, which shows that the final SnS2 nanoplates actually evolve from the initial tin dioxide (SnO2) nanoparticles. In the sulphidizing process of SnO2, nanoplates with rose-like structure are formed. Based on these XRD and FE-SEM results, a formation mechanism is proposed, as illustrated in Figure 5. In the synthesis process, linear PEG serves as a complexing agent for the formation of 3D desert rose-like structure. The oxygen atom at the end of PEG molecular chain after being solved in water will coordinate with metallic species to form Sn4+-PEG complexes. Taking it as nuclei, SnO2 nanoparticles are formed on the end of PEG molecules by hydrolysis and condensation of SnCl4 in solution. Then, the SnO2 nanoparticles convert to SnS2 nanoplates in situ through sulphuration reaction. As PEG prefers to guide the formation of (101) surfaces of SnS2, the nanoplates grow with (101) planes being exposed. Gradually, these nanoplates evolve into 3D rose-like architecture. After carbon coating


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process, a uniform amorphous carbon layer can be obtained on the surface of the (101) oriented SnS2 nanoplates.

Figure 6. Schematic illustration of lithium ion insertion in samples with (101) (a, b) and (001) (c, d) orientations. For 2D SnS2 nanoplates, the orientation can influence the lithiation/delithiation kinetics during cycling. Figure 6a,c display the structure models of SnS2 crystals with exposed (101) and (001) facets, respectively. According to the inherent lithiation behaviour for the layered structure of SnS2, schematic lithiation processes for nanoplates of two samples are depicted in Figure 6b,d. Since both of the samples exhibit 2D nanoplate morphology with finite lateral size and enhanced open-edge, it is notable that sample with (101) orientation enables shorter lithium ion transport paths and also provides more active sites for the electrochemical reaction, as compared to sample with (001) orientation. This suggests that (101) oriented SnS2 nanoplates can facilitate the reversible lithium ion diffusion kinetics and ensure full utilization of the active material, thus can lead to high charge/discharge capacity and excellent rate capability. Also, its smaller size of


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(001) plates contributes to the improved performance, due to a decreased internal strain and limited cracking during the lithiation/delithiation processes.

Figure 7. Cycling performance (a), rate capability (b) and long-term cycling performance (c) of carbon-encapsulated SnS2 nanoplates with oriented (101) plane. The electrochemical properties of the carbon-encapsulated SnS2 nanoplates with oriented (101) plane were evaluated by two-electrode coin cell with metal lithium as counter electrode. First, the cycling performance was measured at a current density of 0.1 A g-1. As illustrated in Figure 7a, the 1st discharge and charge capacities are 1295 mAh g-1 and 1011 mAh g-1, respectively, corresponding to a Coulombic efficiency of 78%. This initial capacity loss is mainly caused by


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the formation of a solid electrolyte interface layer.23-25 In the subsequent cycles, the electrode delivers a high specific capacity of 960 mAh g-1 and excellent cycling stability with a capacity retention of around 95% with respect to the second cycle. Moreover, the voltage profiles of the electrode present practically superimposable curves after the first cycle (SI, Figure S8), which further verifies

the excellent

electrochemical

reversibility of the electrode during

charge/discharge processes. The electrode also exhibits an excellent rate-capability. As depicted in Figure 7b, when cycling at different current densities varing from 0.1 to 2 A g-1, the electrode delivers capacities of 916, 877, 840 and 827 mAh g-1 at current densities of 0.2, 0.5, 1 and 1.5 A g-1, respectively. A high reversible capacity of 796 mAh g-1 can be achieved even at the current density as high as 2 A g-1. When the current density is switched back to 0.1 A g-1, the specific capacity is recovered to 920 mAh g-1. These results indicate that the designed SnS2 nanoplate electrode has a very fast electrode reaction kinetics, which is ascribed to the oriented (101) plane of SnS2 nanoplates and the homogeneous carbon coating film on SnS2 nanoplates. The former provides more acive sites for lithium ion reaction and shortens the lithium ion diffusion distance, while the latter offers a fast electron conduction. The carbon-encapsulated SnS2 nanoplates with oriented (101) plane also exhibit a stable longcycling performance. As depicted in Figure 7c, a stable capacity of ~800 mAh g-1 is maintained for 300 cycles at a current density of 0.5 A g-1, showing only 0.05% cyclic decay per cycle with respect to the first charge capacity. The electrode can also deliver a stable capacity of ~750 mAh g-1 over 150 cycles at 1 A g-1 (SI, Figure S9). The structural morphologies of the carbon-coated (101)-oriented SnS2 electrode before and after 100 cycles at a current density of 1 A g-1 was observed by FE-SEM. As shown in Figure S10 in SI, the electrode remains integrated structure without obvious cracks on the electrode surface.


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The excellent cycling performance is ascribed to the oriented facet preferential for lithium ion uptaking/releasing and the uniform carbon coating layer, which endow a homogeneous electrode reaction and thus a uniform volume change of the electrode, leading to excellent geometrical integrity of the electrode during repeated charge/discharge processes. We compare the performance of this work with the results of published works about SnS2-based systems (SI, Table S2). Obviously, the capacity and rate capability of this work is greatly superior to those of most reported SnS2-based anodes.

Figure 8. Cycling performance (a) and rate capability (b) of carbon coated SnS2 nanoplates with (001) orientation. On the contrary, the electrode of the carbon-coated SnS2 nanoplates with (001) orientation show a poor cycling stability (Figure 8a) and inferior rate capability (Figure 8b), compared to that with (101) orientation (Figure 7). A relatively stable capacity of 833 mAh g-1 in first 50 cycles is delivered and then a fast capacity decline is followed. In a stepwise rate-capability measurement, the electrode of carbon coated SnS2 with (001) orientation displays an obvious capacity decrease with increasing current density. A specific capacity of 547 mAh g-1 is observed at 2 A g-1, which is much lower than that of carbon coated SnS2 with (101) orientation (796 mAh


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g-1). These results demonstrate the remarkable advantages of SnS2 nanoplates with (101) orientation. Of course, carbon coating layer also plays an important role in electrochemical performance. Without carbon layer, even the SnS2 nanoplates with (101) orientation show a gradual capacity degradation after 70 cycles (SI, Figure S11). Moreover, as displayed in Table S3 in SI, charge transfer resistance Rct of (101) oriented SnS2 nanoplates with carbon coating is lower than that of without carbon coating (SI, Figure S12), demonstrating its faster electrochemical reaction kinetics. This is most likely due to the not fully resolved problems with big volume changes during lithiation/delithiation processes for the uncoated sample.30,36,37 Poor electronic conductivity of SnS2 renders the electrode reaction to occur inhomogeneously on the active particle surface, which will lead to a non-uniform volumetric changes, and thus presence of stress inside the particles. The stress could cause particle cracking and the accompanying capacity degradation. In order to elucidate the electrode reaction kinetics of SnS2 nanoplates with different orientations, CV tests were performed (SI, Figure S13). The result indicates that the SnS2 nanoplates with oriented (101) planes possess higher lithium ion diffusion coefficient than that with (001) orientation. This improved lithium ion diffusion should be ascribed to the presence of the efficient ionic transfer pathways with (101) facets being exposed. EIS measurements (SI, Figure S14a) were also conducted to understand the reaction processes of the two electrodes. The simulation of EIS spectra with equivalent circuit reveal that the charge transfer resistance Rct of sample with (101) orientation (105.5 Ω) is much lower than that of sample with (001) orientation (204.8 Ω), suggesting that the charge transfer in (101) oriented


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nanoplates is much easier, which can lead to faster electrochemical reaction kinetics. This lower charge transfer resistance is strongly correlated with the crystal orientation and should be responsible for the exceptional rate capability of sample with (101) planes exposure. Furthermore, the calculated DLi for sample SnS2 with (101) and (001) orientations (SI, Figure S14b) further indicates that SnS2 nanoplates with oriented (101) plane has higher Li ion diffusion coefficient than that of (001) plane. It should be emphasized that the proposed strategy for the oriented (101) crystal growth can be extended to a variety of layered-type electrode materials, which will be benefited from excellent electrochemical properties because of shortened ion diffusion paths and abundant active sites present in such designed microstructure. 4. CONCLUSION In summary, carbon encapsulated SnS2 nanoplates with preferred (101) facets were synthesized through a PEG-assisted hydrothermal method combined with a carbon coating process. When evaluated as anode material for LIBs, the as-prepared material exhibits high specific capacity (960 mAh g-1 at a current density of 0.1 A g-1), superior rate capability of 796 mAh g-1 at a current density as high as 2 A g-1, and excellent cycling stability with only 0.05% cyclic decay rate at 0.5 A g-1 for 300 cycles. These excellent performances are attributed to the designed microstructure with the highly (101) facet-preferred orientation, which builds rapid and durable highways for lithium ion diffusion, and thus ensures fast reaction kinetics. The uniform carbon layer increases the electronic conductivity and buffers the volume variation of SnS2 during cycling. Importantly, the strategy demonstrated here for oriented layer crystal can be


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extended to a variety of layer-structured materials for the application in energy storage and conversion, as well as in chemistry catalysis. ASSOCIATED CONTENT Supporting Information. XRD pattern of the sample without PEG during synthesis, structural data of samples synthesized with and without PEG, FE-SEM, TEM and HR-TEM images of the sample without PEG, XPS spectra of the samples with and without PEG, TG curve of carboncoated SnS2 nanoplates with (101) orientation, XRD patterns and corresponding FE-SEM images of sample with (101) orientation at different stages of the hydrothermal process, selected charge/discharge curves and cycling performance of carbon-coated SnS2 nanoplates with (101) orientation at 1 A g-1, FE-SEM micrographs of carbon-encapsulated (101)-oriented SnS2 electrode before and after cycling for 100 cycles at 1 A g-1, summary of electrochemical performance data of the reported SnS2 based electrode materials, cycling performances of nonand carbon-coated SnS2 nanoplates with (101) orientation at 0.1 A g-1, Nyquist plots of impedance data for the non- and carbon-coated SnS2 nanoplates with (101) orientation in the range of 0.1 Hz to 106 Hz, fitting results from EIS, CV curves and Nyquist plots of non-coated SnS2 samples with (101) and (001) orientations. This information is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Phone: (+86) 10 82376837; Fax: (+86) 10 82376837.


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Table of Contents


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(101) Plane-Oriented SnS2 Nanoplates with Carbon Coating: A High

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