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Fe2O3/SnSSe Hexagonal Nanoplates as Lithium Ion Batteries Anode Yufei Zhang, Jun Yang, Yizhou Zhang, Cheng-Chao Li, Wei Huang, Qingyu Yan, and Xiaochen Dong ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b01537 • Publication Date (Web): 22 Mar 2018 Downloaded from http://pubs.acs.org on March 22, 2018

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ACS Applied Materials & Interfaces

Fe2O3/SnSSe Hexagonal Nanoplates as Lithium Ion Batteries Anode Yufei Zhang,a,b Jun Yang,b Yizhou Zhang,b Chengchao Li,a Wei Huang,b,d* Qingyu Yan,c* Xiaochen Dongb* a

School of Chemical Engineering and Light Industry, Guangdong University of

Technology, Guangzhou 510006, China b

Key Laboratory of Flexible Electronics (KLOFE) & Institute of Advanced Materials

(IAM), Nanjing Tech University (NanjingTech), 30 South Puzhu Road, Nanjing 211800, China. c

School of Materials Science and Engineering, Nanyang Technological University,

Singapore 639798, Singapore. d

Shaanxi Institute of Flexible Electronics (SIFE), Northwestern Polytechnical University

(NPU), 127 West Youyi Road, Xi'an 710072, China *Corresponding authors. E-mail: [email protected]; [email protected]; [email protected]

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ABSTRACT Novel two-dimensional (2D) Fe2O3/SnSSe hexagonal nanoplates were prepared from hot-inject process in oil phase. The resulted hybrid manifests a typical 2D hexagonal nanoplate morphology covered with thin carbon layer. Serving as anode material of lithium ion battery (LIB), the Fe2O3/SnSSe hybrid delivers a outstanding capacity of 919 mA h g-1 at 100 mA g-1 and a discharge capacity of 293 mAh g-1 after 300 cycles at the current density of 5 A g-1. Compared with pristine SnSSe nanoplates, the Fe2O3/SnSSe hybrid exhibits both higher capacity and better stability. The enhanced performance is mainly attributed to the 2D substrate together with the synergistic effects offered by the integration of SnSSe with Fe2O3. The 2D Fe2O3/SnSSe hybrid can afford highly accessible sites and short ion diffusion length, which facilitates the ion accessibility and improves the charge transport. The novel structure and high performance demonstrated here affords a new way for structural design and the synthesis of chalcogenides as LIB anodes.

KEYWORDS: two-dimensional; chalcogenide alloy; Fe2O3/SnSSe; hexagonal nanoplates; lithium ion battery

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INTRODUCTION

Two-dimensional (2D) layered materials, especially transition metal dichalcogenides (TMDs), have drawn significant research attentions owing to the unique properties and wide potential applications in optoelectronics1, catalysis2-5 and energy storage devices8-9. Owing to the weak van der Waals forces inside the layers, TMDs present typical layered structure.6-8 These structure merits also afford them great potential in energy storage.9-11 Among them, tin dichalcogenides draw considerable attentions due to their attractive electrochemical advantages and natural abundance.12-13 The layered hexagonal CdI2 type structured SnS2 and SnSe2 have theoretical Li storage capacities of 645 mAh g-1 and 426 mAh g-1, respectively.14-16 SnS2 possesses a band gap of about 2.1 eV, resulting in poor electrical conductivities of 10-12-10-2 S cm-1.17-18 The low electrical conductivities may impede the charge transfer kinetics when used as lithium ion batteries (LIBs) electrode under high currents. In comparison, SnSe2 possesses a band gap of 1.14 eV with much higher electrical conductivity.19 In addition, pioneering research reported that partial S doping in selenides could optimize the electrical conductivity via increasing charge carrier (hole) concentration. At the same time, the surface sulfur donor states could be enhanced with the sulfidation on the selenides.20-21 Therefore, it is promising to prepare SnSSe compounds to tune the electrochemical and electrical properties simultaneously. Since the diffusion time of ions within the electrodes follows the relationship of t=L2/D, diffusion length and the diffusion coefficient D paly a vital role in determining the diffusion rates. Therefore, it is obvious that 2D structure possessing shorter diffusion length could enhance the electrochemical kinetics as well as the mobility of ions and electrons.22 In this regards, 3



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2D structure is beneficial for structure construction. Furthermore, considering the merits of 2D structured sulfoselenide, it can act as platform for combination with high-capacity material. By forming heterostructures with other high-capacity material, complementary features can be achieved and the energy density can be further increased. Considering the high theoretical capacity of about 1007 mAh g-1, ecofriendness and easy fabrication, Fe2O3 was selected to composite with SnSSe.23-24 In this work, the fabrication of uniform SnSSe hexagonal nanoplates (NPs) and their hybrid heterostructures with Fe2O3 was presented systematically. The SnSSe hexagonal NPs with diameter of 100 nm were synthesized by hot-inject process in oil phase. The Fe2O3/SnSSe hexagonal NPs were subsequently prepared through chemical deposition. Employed as LIB anode material, the Fe2O3/SnSSe hexagonal NPs exhibited a discharge capacity of 919 mAh g-1(100 mA g-1) and maintained a discharge capacity of 293 mAh g-1 after 300 cycles at current density of 5 A g-1. The promising Li storage property can attribute to the elaborate 2D morphology design of Fe2O3/SnSSe hexagonal NPs, as well as the synergistic effects of Fe2O3 and SnSSe. The elaborate structure together with the complementary effects enhanced the electrical conductivity and electrochemical kinetics of the hybrid simultaneously.

EXPERIMENTAL SECTION Tin chloride (SnCl2, 95%), 1-octylamine (99%), oleic acid (technical, 90%), selenous acid (> 98%), sulfur powder (98%), iron (III) acetylacetonate (99%), 1, 2-hexadecanediol (97%,) and 1-octadecene (ODE, technical, 90%) were directly used without further purification. 4


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All synthetic processes were dealt with standard Schlenk line in continuous Ar flow. Preparation of OA-Se Stock solution The OA-Se stock solution was prepared according to the published reference with minor modification.25 2 mmol Selenium acid and 10 mL oleic acid (OA) were mixed into a 100 mL three-neck flask with stirring. Then, degased the mixture with Ar (g) for 30 min and heated to 120 °C. The mixture was heated to about 160 °C and kept for 30 min for reaction. Finally, the resulted clear, light-yellow was achieved with 0.1 M OA-Se. Preparation of SnSSe nanoplate Firstly, 1 mmol SnCl2, 2 mmol sulfur powder was mixed with 5 mL oleylamine (OAM) and 10 mL 1-octadecene (ODE) in a 100 mL three-neck reaction flask. Then, the mixture was flowed by bubbling Ar gas with continuous stirring at ~70 °C for 30 min and formed light yellow solution. Then the three-neck flask containing solution was heated above 100 °C under pure Ar atmosphere to get rid of H2O and O2. After that, gradually heated the mixture to 230 °C followed with the injection of 4 mL OA-Se and maintained for another 30 min. Finally, the solution was cooled down by taking out from the heating mantle. The precipitated brown product was received by centrifugation with hexane. Repeatedly washing progress with acetone and hexane was taken for fully remove the oil phase solvents and dispersed in 20 mL hexane for further use. Preparation of Fe2O3/SnSSe nanoplate The above prepared SnSSe dispersion was ultra-sonicated before use. Then, the SnSSe dispersion was poured into a reaction flask with the mixture of 10 mL ODE, 1 mL OA and 1 mL OAM. The mixture was stirred for creating homogeneous solution. Afterwards, 0.2 5



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mmol Fe(acac)3 and 1 mmol 1,2-hexadecanediol were added into the mixture with stirring under Ar gas flow. The mixture was heated to 180 °C and retained 30 min, followed with heated to ~260 °C for 30 min reaction. The achieved black-brown dispersion was cooled at room temperature. Finally, the product was repeatedly centrifugated in hexane and acetone. With drying in vacuum oven overnight, brown powder product was obtained. Characterization The achieved products were characterized by using X-ray diffraction (XRD, D8 with Cu Kα radiation) for phase analysis. Scanning electron microscopy (SEM, JOEL-7600F), transmission electron microscopy (TEM, JEOL JEM-2010) were used for structure exploration. Elemental analysis was taken with X-ray photoelectron spectroscopy (XPS, PHI 5700). The surface area of the samples was determined from BET measurements by using a Tristar 3020 surface area analyzer. The half coin cells were assembled with lithium metal as the counter, the synthesized material as the anode in glove box. 1 M LiPF6 (ethylene carbonate: dimethyl carbonate=1:1) and Cellgard 2300 was applied as the electrolyte and the separator, respectively. The galvanostatic charge-discharge process was tested on a Neware battery tester (Shenzhen, China) between 0.005-3.0 V with the assembled cell. The cyclic voltammetric (CV) curves were performed on Solartron 1470E electrochemical workstation within 0.005-3.0 V (vs. Li/Li+). The electrochemical impedance spectroscopy (EIS) was tested on a CHI 660D electrochemical workstation (Chenhua, USA).

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RESULTS AND DISCUSSION Scheme 1 shows the synthetic procedure of SnSSe NPs and Fe2O3/SnSSe NPs heterostructures. Firstly, SnS2(OAM)x complex was formed by reaction of SnCl2, S and OAM during heating to 230 °C. After the injection of OA-Se solution at 230 °C and maintaining for another 30 min, uniform SnSSe NPs were formed. After that, the SnSSe nanoplates served as the heterogeneous nucleating sites to anchor Fe2O3 by reacting with Fe(acac)3 and 1,2-hexadecanediol. Finally, uniform hexagonal SnSSe/Fe2O3 composites were formed. Scheme 1. The synthetic illustration of the SnSSe NPs and Fe2O3/SnSSe NPs.

The phase information of SnSSe NPs and Fe2O3/SnSSe NPs were analyzed through XRD (Figure 1). The SnSSe nanoparticles possess a rhombohedral crystal structure (JCPDS 78-9605, a=3.728000 Å, b=3.728000 Å c=6.037000 Å). The major peaks at 14.67 o, 27.63 o, 31.42 o, 40.93 o, 48.86 o, 51.3 o, 59.25 o, 65.77 o, 75.5

o

can be ascribed to the diffraction

planes of (001), (100), (011), (012), (110), (101), (012), (022) of SnSSe phase, respectively. No obvious peaks from other phases are detected, which suggesting a pure phase of SnSSe was achieved. The strongest peak of the SnSSe can be identified to the (011) crystal plane, 7



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which illustrates a preferable growth along the (011) crystal plane. After introducing Fe2O3 to SnSSe and forming Fe2O3/SnSSe heterostructures, weak peaks appear at 26.67°, 30.35°, 38.87°, 43.58°, which can be identified to Fe2O3 phase (JCPDS 04-0755), respectively.

Figure 1. XRD patterns of SnSSe and Fe2O3/SnSSe NPs. The morphology of the SnSSe NPs was investigated using SEM and TEM. The SEM image (Figure 2a, 2b) demonstrates the SnSSe is uniform nanoplates with hexagonal symmetry. Moreover, TEM images (Figure 2c-d) present that the lateral size of the nanoplates is around 100 nm. The inset in Figure 2d gives the high resolution TEM image of an individual SnSSe nanoplate. The lattice distance is around 0.325 nm, ascribing to the (110) planes of SnSSe. The selected area electron diffraction (SAED) pattern of single SnSSe nanoplate (Figure 2e) shows well-defined spots, which suggests the single-crystalline nature of the as grown 2D nanoplates. The spots observed in the SEAD pattern can be assigned to the (110), (112) and (002) lattice spacings. It can be assumed that a and b axes lie flat on the plane of the nanoplate and c axis of (001) plane is perpendicular to it. The TEM image of the SnSSe nanoplate in cross-section view is exhibited in Figure 2f. It shows 8


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that the thickness of SnSSe nanoplate is about 15 nm with thin amorphous carbon layer (3-5 nm) covered on its surface. The amorphous carbon layer may be attributed to the carbonation of the adsorbed capping layer (e.g. OA or OAM). It also illustrates a preferable growth of SnSSe along the (011) crystal plane.

Figure 2. (a, b) SEM images of SnSSe NPs taken at different magnifications; (c) overview of SnSSe NPs lying flat on the TEM grid; (d) the high-resolution TEM image from surface plane; (e) diffraction pattern taken from the direction of figure d; (f) the side view of one single nanosheet. Figure 3 shows the TEM images of Fe2O3/SnSSe hybrid. From Figure 3a, it is clear that the sample retains the hexagonal nanoplate morphology with a lateral dimension of around 100 nm. The HRTEM image (Figure 3b) exhibits the lattice fringes of the SnSSe phase, the calculated 0.28 nm relates with the (011) plane of SnSSe. The lattice of Fe2O3 cannot be directly detected, which may be corresponded with the low crystallinity provided by the synthetic Fe2O3. The TEM image and element mapping of Fe2O3/SnSSe nanoplates (Figure 9



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3c) display the uniform distribution of O, Fe, S, Se, and Sn within the Fe2O3/SnSSe heterostructures. The SEM images and the EDX spectrum (Figure S1) also confirm the presence of O, Fe, S, Se, and Sn elements in the Fe2O3/SnSSe heterostructures.

Figure 3. (a) TEM image of Fe2O3/SnSSe NPs. (b) HRTEM image of Fe2O3/SnSSe NPs. (c) EDX-TEM characterization of Fe2O3/SnSSe NPs. The chemical compositions of the elements in the heterostructures were explored using X-ray photoelectron spectroscopy (XPS). Characteristic peaks of Sn (3s, 3p, 3d, 4d, etc.), Se (3s and 3d), S (2p) and Fe (2p) can be observed. As manifested in Figure 4a, obvious peaks at 167.2, 163.8 and 159.2 eV are assigned to Se3p1/2, S2p and Se3p3/2 in SnSSe, illustrating the coexistence of S and Se.6 The Se 3d spectrum is drawn in Figure 4b. The main peak centered at 53 eV can be deconvoluted into Se 3d5/2 and Se 3d3/2 peaks centered at the position of 53.5 and 54.1 eV, respectively, which reveals the existence of 10


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Se2-.26-27 In the Sn 3d spectrum (Figure 4c), Sn 3d3/2 and Sn 3d5/2 orbital peaks are observed at 493.5 and 485.6 eV, respectively, with a characteristic peak separation of 8.5 eV, indicating the existence of Sn(IV).28 The binding energy of 485.6 eV is indexed to the existing of S-Sn bond. The binding energy of Se 3d and Sn 3d both shift to higher values, suggesting the partial oxidation of Se in the sample.29-30 The Fe spectrum is presented in Figure 4d, two characteristic peaks centered at 710.8 and 725 eV are related to Fe 2p3/2 and Fe 2p1/2, respectively.31 Other peaks at 717.8 eV and 733 are the satellite peaks of Fe 2p1/2 and Fe 2p3/2, respectively, which are the feature peaks of Fe2O3.32-33

Figure 4. XPS spectra of (a) S 2p and Se 3d regions, (b) Se 3d region, (c) Sn 3d region, and (d) Fe 3d region in Fe2O3/SnSSe NPs. In order to evaluate the as-prepared SnSSe NSs, systematic electrochemical measurements with the assembled cell were tested at room temperature. Figure 5a depicts the representative first five cyclic voltammogram (CV) curves of SnSSe electrode at 0.1 mV s-1 11



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in 0.005-3.0 V. There are two pairs of peaks appeared in the charging-discharging process, relating with the different Li insertion/extraction progress. In the first discharge process, peaks were found at 1.81 V, 1.21 V, 0.67 V and 0.11 V, respectively, and corresponding oxidation peaks occurred at 0.52 V and 1.86 V during the first charging process. The lithiation process of tin dichalcogenides (Q = S or Se) is expressed as following equation:34-36 SnQ2 + xLi+ + xe-→4 LixSnQ2

(1)

LiySnQ2 + (4- y)Li+ + (4-y)e-→Sn + 2Li2Q (1 ≤ x ≤y ≤ 2)

(2)

Sn + 4.4Li+ + 4e-↔ 4Li4.4Sn

(3)

SnQ2 + 4Li+ + 4e- ↔ Sn + 2Li2Q

(4)

The reduction peak at 1.81 V observed only during the first discharge process indicates irreversible reactions. The peak could be attributed to the reaction of the lithium embedded in the SnSSe layer, which could be summarized as reaction (1).35, 37 Another reduction peak at 1.21 V related with the transformation from SnSSe to tin metal and Li-S compound(Equation 4).14 The alloying reaction (Equation 3) also taken place as indicated in the reduction peak of 0.67 V.38 Another peak at 0.11 V observed only in the first discharge process can be indexed to the formation of solid electrolyte intermediate phase (SEI), which results in the loss of discharge capacity in the following cycles.35, 37 The oxidation peak at 0.52 V corresponds to the lithium removal reaction from Li4.4Sn alloy (Equation 3). While the other peak at 1.86 V may originate from the reverse reaction in equation 4 and the reformation of the SnSSe phase.39 The resulted CV plots in the subsequent cycles overlap together suggesting the highly reversible Li+ implantation 12


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process. Figure 5c presents the representative CV curves of the Fe2O3/SnSSe electrode. It can be observed that the peak positions shown in the curves are basically the same as those of the SnSSe NPs. The reduction peak at 1.25 V during the first discharge is related with the reaction of equation 4 and the insertion reaction of Li+. The oxidation peak at 1.89 V has a significant enhancement, representing both the formation of SnSSe phase and the oxidation reaction of metallic Fe. Figure 5b and 5d depict the first five galvanostatic charge-discharge (GCD) curves of SnSSe and Fe2O3/SnSSe electrodes at 100 mA g-1. It is clearly observed from Figure 5b that the potential plateaus in accordance with the CV curves. An initial discharge capacity of 1621 mAh g-1 and a charge capacity of 858 mAh g-1 were possessed by SnSSe electrode with the first Coulombic efficiency of around 53 %. The initial capacity loss may due to the incomplete conversion reactions together with the formation of the SEI layer. The discharge capacity of SnSSe electrode decreased to ~600 mAh g-1 and remained almost the same afterwards, demonstrating the stability of the electrochemical reactions. Figure 5d is the representative charging and discharging curves for the Fe2O3/SnSSe electrode. The first discharge capacity of Fe2O3/SnSSe electrode can reach 1560 mAh g-1. Although the first discharge capacity is not as high as SnSSe electrode, the subsequent charge and discharge capacity maintained at 919 mAh g-1 with a Coulombic efficiency of 95%. The overlapping of charge and discharge curves in the following cycles suggests the excellent stability of Fe2O3/SnSSe electrode.

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Figure 5. CV curves tested at 0.1 mV s-1 in within 0.005-3.0 V of (a) SnSSe NSs and (c) Fe2O3/SnSSe NPs. The first five GCD profiles between 0.005 and 3.0 V of (b) SnSSe NPs and (d) Fe2O3/SnSSe NPs at 100 mA g-1. The lithium storage properties of the as-synthesized Fe2O3/SnSSe NPs and SnSSe NPs electrodes were systematically measured to explore the effects with the combination of Fe2O3. It is clearly demonstrated that the rate performance of Fe2O3/SnSSe NPs is better than that of pure SnSSn NPs (Figure 6a). The Fe2O3/SnSSe electrode can deliver discharge capacities of 919, 840, 791, 706, 605 and 424 mAh g-1 during the 5th cycle at current densities of 100 mA g-1, 200 mA g-1, 500 mA g-1, 1 Ag-1, 2 A g-1 and 5 A g-1, respectively. Furthermore, the electrode was still able to deliver a high capacity of 940 mAh g-1 when returning the current density to 100 mAg-1. However, the SnSSe electrode only maintained a capacity of 691, 612, 503, 473, 385 and 308 mAh g-1 during the 5th cycle at the same 14


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current density. It can only maintain a capacity of 553 mAh g-1 at 100 mA g-1. Figure 6b shows the stability performance of SnSSe and the Fe2O3/SnSSe electrode for 100 cycles at current density of 200 mA g-1. The Fe2O3/SnSSe electrode can maintain a capacity of 755 mAh g-1 after 100 cycles while SnSSe electrode can only maintain a capacity of 433 mAh g-1. The cycle stability of Fe2O3/SnSSe electrode was tested at a current density of 5 A g-1, as exhibited in Figure 6c. The Fe2O3/SnSSe electrode has excellent electrochemical stability, which can maintain a capacity of 293 mAh g-1 after 300 cycles with the Coulombic efficiency of about 95 %. The electrochemical impedance spectroscopy (EIS) was tested with SnSSe and Fe2O3/SnSSe to investigate the inner electrochemical behavior and fitting with the corresponding circuit (Figure 6d and the insets). In this circuit, the electrolyte resistance within the battery is marked as Re and Rf represents the internal resistance. Rct represents the electrode/electrolyte interface charge transfer impedance. CPE1 and CPE2 represent the resistance related with SEI and electric double layer capacitance. ZW is the Li+ diffusion related with the Warburg impedance. As indicated in Figure 6d, the semicircle in the high frequency region represents Rf and CPE1 and the low frequency region gives information about ZW. It can be observed that the semicircle of the Fe2O3/SnSSe electrode is much smaller than that of the SnSSe electrode, which suggested the smaller internal resistance of the Fe2O3/SnSSe electrode. The response of the Fe2O3/SnSSe electrode in the low frequency region is close to the ideal diffusion, indicating fast ion transfer inside the material. The EIS results further demonstrate that the Fe2O3/SnSSe electrode presents a smaller resistance than the SnSSe electrode, resulting in better electrochemical performance. These comparisons show the better performance of 15



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Fe2O3/SnSSe electrode than SnSSe electrode, which may be due to the synergistic effects of Fe2O3 and SnSSe NPs. Firstly, the two-dimensional SnSSe NPs can provide large specific surface area for electron/ion transportation, facilitating the insertion of Li+ even at a large current density. Secondly, the two-dimensional morphology provided by the material can effectively accommodate the volume expansion generated during cycling, which helps maintain stability. Thirdly, the combination of Fe2O3 not only contributes more active sites and capacity to the composite, but also helps enhance the conductivity during charging-discharging process.

Figure 6. (a) The rate performance of Fe2O3/SnSSe NPs and SnSSe NPs. (b) The stability performance of Fe2O3/SnSSe NPs and SnSSe NPs at 200 mA g-1 for 100 cycles. (c) The long cycling performance of Fe2O3/SnSSe NPs at current density of 5 Ag-1. (d) Nyquist plots of Fe2O3/SnSSe NPs and SnSSe electrode. To deeply explore the electrochemical kinetics inside the Fe2O3/SnSSe NPs, CV plots 16


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recorded with various scan rates are depicted in Figure 7a, which shows two pairs of obvious peaks with similar shapes. The cathodic peak shifts towards negative with increasing scan rate, while the anodic peaks shift to positive side with increasing scan rate. In addition, as enlarging scan rates, the peak current increases almost linearly (Figure 7b). It suggested that a surface-controlled electrochemical process may happen. The achieved CV curves also provide detailed information for further examination with the reaction. Learnt from Duan and his coworkers, a proposed general equation can be applied for the quantitatively calculation with the capacitive contribution. They expressed that the particular current obtained at a specific voltage can be regarded as the total effects by two components. One is controlled by the surface capacitive effects and the other is offered by diffusion-controlled Li+ insertion process. Thus, the equation can be described as follows. i (V)=k1 ν +k2 ν1/2 To devide ν1/2 in the two sides of the equation, it can be rewritten as i (V)/ ν1/2=k1 ν1/2 +k2. Thus, one specific current at a fixed potential can be divided into the contributions of diffusion-controlled Li+ insertion-k2 ν1/2 and the capacitive effect-k1ν. By plotting the sweep rates dependence of the currents as in Figure 7c, constant k1 and k2 at a fixed potential can be known exactly. The fitted contributions from pseudocapacitance and intercalation at 1 mV s-1 are plotted in Figure 7d. The whole contribution of the current provided by the capacitive effect is calculated to be about 40.76 %. The diffusion of lithium ions mainly occurred at around the anodic and cathodic peaks. More importantly, the 2D structure and the high electronic conductivity offered by the Fe2O3/SnSSe NPs, Li anions could easily diffuse into the layer gaps within the nanosheets, which leads to capacitive surface 17



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reactions. The capacitive surface reactions accelerate the transfer kinetics and improve the charging/discharging rates, resulting in high capability even at high current density.40-41

Figure 7. (a) CV profiles of Fe2O3/SnSSe NPs recorded with various scan rates. (b) Relationship of charge peak currents with various scan rates. (c) The plots fitting with ν1/2 to i/ν1/2. (d) CV curves of Fe2O3/SnSSe NPs with pseudocapacitive fraction shown by the darkly cyan region at 1 mV s-1.

CONCLUSION In summary, Fe2O3/SnSSe NPs and SnSSe hexagonal NPs have been controllably synthesized via oil phase process. The obtained Fe2O3/SnSSe hexagonal NPs delivered a discharge capacity of 919 mAh g-1 at the current density of 100 mA g-1 and a high discharge capacity of 293 mAh g-1 even after 300 cycles at the current density of 5 A g-1 when tested as LIB anode. The two-dimensional SnSSe alloy NPs can serve as a conductive platform 18


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and help maintain the electrochemical kinetics. With the introduction of Fe2O3, enhanced electrical conductivity and additional capacity are found in the obtained Fe2O3/SnSSe NPs, which can serve as a potential LIB electrode material. Furthermore, this work provides a promising method for the design and applications of novel two-dimensional dichalcogenides.

SUPPORTING INFORMATION In Supporting Information file, the SEM images, EDS spectra of SnSSe NPs and Fe2O3/SnSSe NPs are available. Moreover, N2 adsorption and desorption isotherms were also provided. The cycling comparision of Fe2O3/SnSSe NPs, Fe2O3 and Fe2O3/SnSSe NPs is also given.

ACKNOWLEDGMENT The project was supported by NNSF of China (61525402, 61728401, 5161101159), National Postdoctoral Program for Innovative Talents (BX201600072).

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