Facile Synthesis of a MoS2 and Functionalized Graphene

Letter www.acsami.org

Facile Synthesis of a MoS2 and Functionalized Graphene Heterostructure for Enhanced Lithium-Storage Performance Beibei Wang,†,‡ Yin Zhang,⊥ Jin Zhang,† Ruoyu Xia,† Yingli Chu,† Jiachen Zhou,† Xiaowei Yang,† and Jia Huang*,†,‡ †

School of Materials Science and Engineering, Tongji University, Shanghai 201804, P. R. China Key Laboratory of Advanced Civil Engineering Materials, Tongji University, Ministry of Education, Shanghai 201804, China ⊥ School of Science, MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, Xi’an Jiaotong University, Xi’an 710049, P. R. China ‡

S Supporting Information *

ABSTRACT: A facile strategy was designed for the in situ synthesis of MoS2 nanospheres on functionalized graphene nanoplates (MoS2@f-graphene) for use as lithium-ion battery anode materials. A modified Birch reduction was used to exfoliate graphite into few-layer graphene followed by modification with functional groups. Compared to the most common approach of mixing MoS2 and reduced graphene oxide, our approach provides a way to circumvent the harsh oxidation and destruction of the carbon basal planes. In this process, alkylcarboxyl functional groups on the functionalized graphene (f-graphene) serve as sites where MoS2 nanospheres crystallize, and thus create bridges between the MoS2 nanospheres and the graphene layers to effectively facilitate electronic transport and to avoid both the aggregation of MoS2 and the restacking of graphene. As anode materials, this unique MoS2@f-graphene heterostructure has a high specific capacity of 1173 mAh g−1 at a current density of 100 mA g−1 and a good rate capacity (910 mAh g−1 at 1600 mA g−1). KEYWORDS: molybdenum disulfide, functionalized graphene, lithium-ion battery anode, heterostructure, modification, composites

W

complexes10,11 and layer-by-layer MoS2/graphene-like composites.12,13 These composites partly enhance the specific capacities, rate capabilities, and cycle stabilities of LIBs. The most common approach is mixing MoS2 and rGO with the aim of enhancing electrical conductivity while retaining the high lithium storage capacity of MoS2.8,9,14 With the conductive carbon network, these strategies can provide electron transport and suppress the polysulfide shuttling effect of MoS2. However, these nanocomposites still do not completely solve the low electrical conductivity issue due to the intrinsic property of rGO, which leaves a lot of irreversible chemical damage in the layer structures after reduction. Thus, designing a structure with excellent stability and good electric conductivity is essential for enhancing the performance of MoS2/C-based LIBs.

ith advantages such as high energy densities, a long cycle life, and environmental benefits, lithium-ion batteries (LIBs) have recently become important parts of energy sources for portable electronics and electric vehicles.1,2 Yet LIBs still suffer from several problems that limit increasing practical demands, and one such problem is the relative lower specific capacities of LIBs.3 In recent years, molybdenum disulfide has received significant attention because of its high theoretical capacity (669 mAh g−1), low-cost, and environmental friendliness.4 However, similar to lithium sulfide batteries, MoS2 suffers from a polysulfide shuttling effect that can result in continuous capacity fading during cycling. Moreover, MoS2 has limited electrical conductivity, and this leads to significant capacity loss and limits commercialization. In response to these problems, recent research has focused on reengineering MoS2/C-based nanocomposites,5−13 such as MoS2/graphite nanocomposites,7 MoS2/reduced graphene oxide (rGO) composites,8,9 MoS2/carbon nanotube (CNT) © XXXX American Chemical Society

Received: January 6, 2017 Accepted: April 4, 2017 Published: April 4, 2017 A

DOI: 10.1021/acsami.7b00248 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Letter

ACS Applied Materials & Interfaces

Figure 1. Schematic illustration of (a) pristine graphite, (b) f-graphene, and (c) MoS2@f-graphene. (d) TEM (SAED inset) and (e) HRTEM images of f-graphene. (f) SEM image, (g) TEM image (SAED inset), (h) HRTEM image, and (i−l) elemental mapping images of MoS2@f-graphene.

Figure 2. (a) Raman spectra of pristine graphite, f-graphene, and MoS2@f-graphene. (b) XRD spectra of MoS2@f-graphene, pure MoS2 nanospheres, and f-graphene. S 2p XPS survey spectra of (c) pure MoS2 and (d) MoS2@f-graphene.

To address these challenges, we designed a unique MoS2@fgraphene heterostructure (Figure 1a−c) with MoS2 nanospheres grown around the functional groups on the surfaces

and edges of f-graphene, which was functionalized via a modified Birch reaction.15−17 During the reaction, graphite was exfoliated by ions and modified with functional groups, B


Letter


of MoS2@f-graphene. With an average diameter ranging from 200 to 500 nm, the flower-like MoS2 nanospheres grew on the surface and at the edges of f-graphene. The corresponding selected area electron diffraction (SAED) pattern of MoS2@fgraphene in Figure 1g shows the hexagonal structure of MoS2. The high resolution transmission electron microscope (HRTEM) image of MoS2@f-graphene in Figure 1h indicates that the MoS2 nanospheres had a greater layer spacing (larger than 0.615 nm), and this was ascribed to the flower-like MoS2 structure packed the functional groups of f-graphene. Meanwhile, the MoS2 nanospheres between the layers prevented the f-graphene layers from restacking. Figures 1i−l show that the elements, including Mo and S, were distributed evenly on a large scale, and this indicates a uniform distribution of MoS2 on f-graphene. We believe that the functional bands on the surface and at the edges of f-graphene play a vital role in the formation of MoS2@f-graphene since they enabled a good dispersion of fgraphene in water and also induced covalent bonding with MoS2 in the hydrothermal reaction. As a result, the MoS2 nanospheres did not “fall off” f-graphene easily, and the composite remained stable without any remarkable volume change during the lithium intercalation and extraction. The Raman spectra of pristine graphite, f-graphene, and the MoS2@f-graphene are given in Figure 2a. The Raman spectrum of pristine graphite has a weak D peak at 1352 cm−1 due to layer edges and initial defects. The two sharp peaks correspond to G peak at 1580 cm−1 and 2D peak ∼2700 cm−1.16 After functionalization, f-graphene shows a higher D peak, and the D/G ratio (ID/IG) increased from 0.243 (graphite) to 0.773 (fgraphene), which suggests that functionalization was successfully introduced.16,18 And the existence of the “O−H”, “CO”, and “C−O” groups of f-graphene shows that the functional groups effectively attached (Figures S2 and S4b).18 After the hydrothermal growth of MoS2 on the f-graphene, characteristic peaks of hexagonal MoS2 appeared. The E12g peak at 372 cm−1 originated from the opposite vibration of two S atoms with one Mo atom, and the A1g peak at 402 cm−1 was associated with the out-plane vibration of only S atoms.19 Another strong peak of MoS2 that appeared at 451 cm−1 was ascribed to 2LA (M).20 The broadness of the three MoS2 peaks indicated that the particle size of MoS2 was on the nanoscale and that they grew successfully on f-graphene. In addition, we also employed X-ray diffraction (XRD) on samples of MoS2@f-graphene, pure MoS2, and f-graphene. The diffraction peaks of pure MoS2 and f-graphene agreed well with the standard diffraction patterns of hexagonal MoS2 (JCPDS # 37−1492) and hexagonal graphite (JCPDS # 41−1487), respectively. Note that after functionalization, the (002) peak of f-graphene was wider than that of pristine graphite, which indicated less crystallinity of f-graphene. The (002) diffraction peak moved to a smaller angle (0.34 nm) in f-graphene with the presence of functional groups. When f-graphene and MoS2 were combined, the MoS2@f-graphene composite displayed only three obvious diffraction peaks, and these corresponded to the (002), (100), and (110) planes of hexagonal MoS2, indicating the poor crystallinity of MoS2. Additionally, the obvious broadening of all of the diffraction peaks suggests that nanoscale MoS2 was synthesized. The textual properties of MoS2@f-graphene was also characterized using N2 adsorptiondesorportion isotherm measurements (Figure S3). The Brunauer−Emmett−Teller (BET) surface area of MoS2@fgraphene was calculated to be 72 m2 g−1, much higher than

producing f-graphene, which maintained good conductivity and improves solubility in water. In the hydrothermal reaction that followed, MoS2 nanospheres tended to nucleate and grow around the functional groups on f-graphene because of the decreased nucleation energy barrier. With functional groups acting as connections between MoS2 nanospheres and graphene layers, MoS2 nanospheres do not aggregate and the graphene layers cannot restack. Meanwhile, electron/ion channels are facilitated. As a result, the unique heterostructure of MoS2@f-graphene has many merits as a material for LIB anodes. These include (a) a good electrical channel for fast electron transfer through the electrode because of the good conductive f-graphene matrix, (b) a stable network structure that leads to excellent performance during electrochemical cycling, and (c) a large electrode/electrolyte contact area and specific surface area that yield a high specific capacity because of the intercalated heterostructure. Indeed, the MoS2@f-graphene heterostructure has a high specific capacity of 1173 mAh g−1 at 100 mA g−1 and a good rate capacity (910 mAh g−1 at 1600 mA g−1). Figure 1a illustrates the fabrication processes for f-graphene and MoS2@f-graphene. Functionalization of graphene was carried out via a modified Birch reduction method,15,16 which is an alkali metal reduction process that takes place in dissolved in liquid ammonia. In ammonia, the electrons of alkali metals are taken up by ammonia molecules, forming alkali metal-ammonia complex ions and ammonia radical anions. As shown in Figure 1a, as charges transfer from ammonia anions to the graphite layers, the alkali metal-ammonia complex ions are gradually intercalated into the graphite. Meanwhile, lattice electrostatic interactions replace the π−π interactions between adjacent graphite layers, resulting in weakened interactions and increased layer spacing. In the meantime, the “-(CH2)5COOH” functional groups are introduced onto the f-graphene sheets by reaction of the ammonia radical anions and the graphene layers. These functional groups assist the alkali metal-ammonia complex ions in separating the graphite to few layer graphene.16,18 After complete evaporation of the liquid ammonia and adequate removal of impurities, f-graphene successfully forms (Figure 1b). Figure 1d, e show the transmission electron microscope (TEM) images of f-graphene, which displays a complete and uniform two-dimensional (2D) structure with few layers (less than 10 in Figure 2e and Figure S1d) and high transparency. With hydrophilic groups -(CH2)5COOH, f-graphene layers do not assemble and can disperse well in water. Thus, fgraphene was used as a substrate for the nucleation and growth of MoS2 nanoparticles in the following hydrothermal reaction, as depicted in Figure 1c. The selective growth of MoS2 on fgraphene was attributed to the interaction between the functional groups on f-graphene and the molybdenum precursors. The functional groups on f-graphene decreased the nucleation energy barrier, thus resulting in effective nucleation and growth of MoS2. MoO42− was likely to locate near these functional groups and to be reduced to MoS2 on fgraphene during the hydrothermal reaction (see the Supporting Information for synthesis details). The MoS2 crystal nucleus was then inclined to grow around a functional group and extend centrifugally. This led to good structure stability during lithiation and delithiation. Additionally, the flower-like MoS2 nanospheres grew on the surface and at the edge of f-graphene, and this effectively inhibited the layer-by-layer stacking of fgraphene. Figures 1f, g, and h (Figure S1c, f) show the images C


Letter


Figure 3. (a) First three cycles of the CV curves for MoS2@f-graphene at a scan rate of 0.1 mV s−1. (b) Charge/discharge curves of MoS2@fgraphene at a current density of 100 mA g−1 measured in a voltage range from 0.01 to 3.0 V. (c) Rate performance of MoS2@f-graphene. (d) Charge/discharge cycling performances of MoS2@f-graphene, MoS2/graphite, and MoS2. (e) Charge/discharge cycling performance of MoS2@fgraphene at a current density of 400 mA g−1. (f) Nyquist plots of MoS2@f-graphene, MoS2 /graphite, and MoS2. Inset equivalent circuit model of the studied system.

pure MoS2 nanospheres (36.4 m2 g−1). All these results are consistent with the SEM (scanning electron microscope) and TEM images shown in Figure 1. The XPS spectra of pure MoS2 and MoS2@f-graphene are given in Figures 2c, d and Figure S4. As seen in Figure S4a, MoS2@f-graphene contained a large amount of C, Mo, and S with a tiny amount of O, which indicated the coexistence of MoS2 and f-graphene in the MoS2@f-graphene composites. As shown in the C 1s spectrum of MoS2@f-graphene (Figure S4b), the intensities of the “−C−O” group (at 286.7 eV) and the “−CO” group (at 287.8 eV) were weak, and this implied that the functionalization of pristine graphite did not cause any unnecessary defects and that f-graphene maintained the original structure of graphene.16 The Mo 3d spectra in Figures S4c, d exhibited characteristic of Mo4+, suggesting that Mo (IV) was dominant in the MoS2 and MoS2@f-graphene samples. In the high resolution S 2p spectra shown in Figures 2c, d, the peaks at 162.6 and 161.4 eV corresponded to the S 2p1/2 and S 2p3/ 2 orbitals of divalent sulfide ions (S2+), respectively.21 In the S 2p spectrum of MoS2@f-g, another peak at 164.1 eV indicated the presence of S−C bonds, as reported in the literature.9 This peak was attributed to the reaction of S atoms with the

functional groups and with the edges of f-graphene, resulting in a bridge between f-graphene and the MoS2 nanospheres. To further explore the practical applications of MoS2@fgraphene, we fabricated it into LIBs and evaluated its electrochemical performance. Figure 3a shows the first three cycles of cyclic voltammetry (CV) for the MoS2@f-graphene electrode at 0.1 mV s−1 and in a voltage range of 0.01−3.0 V. Two reduction peaks at 0.32 and 0.81 V were observed in the first cathodic scan. The weak peak at 0.81 V was attributed to the intercalation of Li ions into the MoS2 lattice to form LixMoS2, and this was similar to the MoS2/carbon composites reported previously.11,12 The peak at 0.32 V corresponded to the decomposition of MoS2: MoS2 + 4Li → Mo + 2Li2S.22 In the subsequent reverse anodic scan, the weak peak at 1.86 V was assigned to the incomplete oxidation of Mo into MoS2, and the broad peak at 2.38 V was assigned to the partial delithiation of Li2S into S.23 In the next two electrochemical cycles, the two peaks at 1.19 and 1.98 V were assigned to the association of Li with S and with MoS2, respectively.24−26 The presence of stable redox peaks during cycling indicated the chemical stability of MoS2@f-graphene during lithiation and delithiation. The explanation for this is that f-graphene improved the electric D


Letter


heterostructure electrode, MoS2 /graphite electrode, and the pure MoS2 nanospheres electrode, and these results are shown in Figure 3f. The end of the high-frequency semicircle was attributed to the resistance of the electrode/electrolyte interface (Rct and CPE), and the slope of the inclined line corresponded to the Warburg impedance (Zw), which was associated with lithium-diffusion within the electrode materials.29 According to the EIS equivalent circle, the Rct values were 87.4, 114.3, and 167.0 Ω for the MoS2@f-graphene, MoS2/graphite, and pure MoS2 electrodes, respectively. The MoS2@f-graphene electrode had an apparent lower interface resistance, Rct, than the MoS2/ graphite electrode or the pure MoS2 nanospheres electrode.26 These results suggested that the structure of the MoS2@fgraphene heterostructure effectively reduced the transfer resistance and enhanced the ionic conductivity. We characterized the MoS2 and MoS2@f-graphene electrodes using SEM before and after cycling to explore the stabilization mechanism further. Before cycling, the MoS2@fgraphene electrode (Figure 4b) appeared uniform and largely

conductivity of pure MoS2, and also provided a platform to prevent the intermediate lithium polysulfide products from dissolving.12,27 Figure 3b shows the first, second, and 25th charge and discharge curves of the MoS2@f-graphene electrode measured at 100 mA g−1. The initial discharge and charge capacities of MoS2@f-graphene were 1464 and 1084 mAh g−1, respectively, with a relatively high Coulombic efficiency of 74%. The irreversible capacity loss in the first cycle was mainly ascribed to the formation of a solid electrolyte interface (SEI) film.12,13,28 The Coulombic efficiency remained as high as 92% in the following cycles with a high reversible capacity of 1176 mAh g−1, which was attributed to the stable and unique heterostructure of MoS2@f-graphene. After 25 cycles, the charge and discharge curve kept a similar shape to that of the second cycle, suggesting that the heterostructure of MoS2@fgraphene was recovered during the charge and discharge processes. The rate capacity of the MoS2@f-graphene heterostructure was measured and is shown in Figure 3c. The assembled halfcell was first measured at a current density of 0.1 A g−1, and then the current densities was increased from 0.2 to 0.4, 0.8, and 1.6 A g−1. The results show that the MoS2@f-graphene heterostructure has an excellent rate capacity with average discharge capacities of 1173, 1050, 1004, and 980 mAh g−1 at current densities of 0.1, 0.2, 0.4, and 0.8 A g−1, respectively. Even with a current density as high as 1.6 A g−1, the capacity still reached 910 mAh g−1. Surprisingly, after the deep charge and discharge testing at 1.6 A g−1, MoS2@f-graphene retained an average capacity as high as 1169 mAh g−1 when the current density fell back to 0.1 A g−1. Therefore, the incorporation of fgraphene enhanced the specific capacity of the MoS2@fgraphene significantly and also improved the cycling stability because of the robust structure between f-graphene and the MoS2 nanospheres. In addition to evaluating the electrochemical performance of the MoS2@f-graphene heterostructure, the MoS2/graphite and pure MoS2 electrodes were also investigated. As shown in Figure 3e, the initial discharge capacities of the MoS2@fgraphene, MoS2/graphite, and pure MoS2 electrodes were 1407, 780, and 1149 mAh g−1, respectively. The cycling stabilities of MoS2/graphite and pure MoS2 were limited, and thus their capacities decreased to 361 and 228 mAh g−1, respectively, after 100 cycles. However, the MoS2@f-graphene composite exhibited a remarkable stability because of its unique heterostructure. The specific capacity of MoS2@f-graphene maintained a value as high as 1220 mAh g−1 after 25 cycles and 1064 mAh g−1 after 100 cycles. Our MoS2@f-graphene composite exhibited decent LIB performance compared to previously reported MoS2/graphite nanocomposites, MoS2/ rGO composites, MoS2/CNT complexes, and even layer-bylayer structured MoS2/graphene composites.7−13 Moreover, the MoS2@f-graphene exhibited excellent cycling stability at 400 mA g−1 with a capacity of 957.7 mAh g−1 after 60 cycles, as seen in Figure 3e. The specific capacity increased in the first 20 cycles, and we believe that this was because of the activation of the materials during lithiation and delithiation. F-graphene was further exfoliated by lithium ions during the first several cycles, and thus the specific capacity of the MoS2@f-graphene heterostructure increased. To better understand the prominent electrochemical behavior of the MoS2@f-graphene heterostructure in comparison with that of MoS2, we also carried out electrochemical impedance spectroscropy (EIS) on the MoS2@f-graphene

Figure 4. SEM images of (a) the MoS2 electrode and (b) the MoS2@fgraphene electrode before cycling. (c) SEM images of the MoS2 electrode and (d) the MoS2@f-graphene electrode after cycling.

crack-free, while the MoS2 electrode (Figure 4a) had some cracks due to the aggregation of MoS2 nanospheres. As shown in Figure 4c, the flat surface of the MoS2 electrode presented SEI films that continuously formed during the electrochemical reaction. Meanwhile, these cracks would have a significant impact on the electrical properties of electrodes. With lithium ion insertion/extraction during cycling, these permanent structural changes (the formation of an SEI layer and aggregation of MoS2 nanospheres) resulted in capacity loss.11 However, as seen in Figure 3d, MoS2@f-graphene had a rough surface with narrow and short cracks, which suggested that there were lower volume changes within the MoS2@f-graphene electrode, and this would not cause continuous capacity loss. The good performance of MoS2@f-graphene was mainly attributed to the unique heterostructure with MoS2 nanospheres grown on f-graphene. The excessive volume expansion caused by the formation of LixMoS2 was effectively limited by the robust structure of f-graphene and the connection between MoS2 nanospheres and f-graphene. This resulted in a stable E


Letter


(JCYJ201419122040621), the Fundamental Research Funds for the Central Universities, and the 1000 Youth Talent Plan.

structure and good cycling performance. Additionally, the unique heterostructure offered extra space between the fgraphene layers, which were exfoliated by MoS2 nanospheres during cycling. Thus, MoS2@f-graphene has a high capacity and good cycling stability. In summary, a heterostructure consisting of f-graphene and MoS2 nanospheres was successfully designed and synthesized through a facile modified Birch reduction and hydrothermal method. Such a heterostructure formed a perfect network between the functionalized graphene and the MoS2 nanospheres, and resulted in an eletronic channel and a stable struture. Compared to the pure MoS2 (642 mAh g−1) and MoS2/graphite (908 mAh g−1) electrodes, the MoS2@fgraphene heterostructure exhibited a better energy performance with a higher specific capacity of 1173 mAh g−1 at 100 mA g−1 and a good rate capacity of 910 mAh g−1 at 1600 mA g−1. The better performance was ascribed to the formation of the heterostructure, in which MoS2 packed the functional bands of f-graphene. As a result, MoS2 nanospheres did not fall off the layers and resulted in a stable heterostucture without a remarkable volume change during lithiation and delithiation. Additionally, f-graphene compensated for the shortage of the conductivity of MoS2. Therefore, we believe this heterostructure can be applied to anode materials for the development of LIBs with a high energy and power density as well as a long cycle life.

■

■

(1) Dong, X.; Chen, L.; Liu, J.; Haller, S.; Wang, Y.; Xia, Y. Environmentally-Friendly Aqueous Li (or Na)-Ion Battery with Fast Electrode Kinetics and Super-Long Life. Sci. Adv. 2016, 2, e1501038. (2) Tavassol, H.; Jones, E. M. C.; Sottos, N. R.; Gewirth, A. A. Electrochemical Stiffness in Lithium-Ion Batteries. Nat. Mater. 2016, 15, 1182−1187. (3) Bresser, D.; Passerini, S.; Scrosati, B. Leveraging Valuable Synergies by Combining Alloying and Conversion for Lithium-Ion Anodes. Energy Environ. Sci. 2016, 9, 3348−3367. (4) Tan, C.; Zhang, H. Two-Dimensional Transition Metal Dichalcogenide Nanosheet-Based Composites. Chem. Soc. Rev. 2015, 44, 2713−2731. (5) Ren, D.; Hu, Y.; Jiang, H.; Deng, Z.; Petr, S.; Jiang, H.; Li, C. SaltTemplating Protocol to Realize Few-Layered Ultrasmall MoS2 Nanosheets Inlayed into Carbon Frameworks for Superior LithiumIon Batteries. ACS Sustainable Chem. Eng. 2016, 4, 1148−1153. (6) Qu, Q.; Qian, F.; Yang, S.; Gao, T.; Liu, W.; Shao, J.; Zheng, H. Layer-by-Layer Polyelectrolyte Assisted Growth of 2D Ultrathin MoS2 Nanosheets on Various 1D Carbons for Superior Li-Storage. ACS Appl. Mater. Interfaces 2016, 8, 1398−1405. (7) Zhao, H.; Zeng, H.; Wu, Y.; Zhang, S.; Li, B.; Huang, Y. Facile Scalable Synthesis and Superior Lithium Storage Performance of BallMilled MoS2-Graphite Nanocomposites. J. Mater. Chem. A 2015, 3, 10466−10470. (8) Zhao, C.; Wang, X.; Kong, J.; Ang, J. M.; Lee, P. S.; Liu, Z.; Lu, X. Self-Assembly-Induced Alternately Stacked Single-Layer MoS2 and Ndoped Graphene: A Novel van der Waals Heterostructure for LithiumIon Batteries. ACS Appl. Mater. Interfaces 2016, 8, 2372−2379. (9) Choi, M.; Koppala, S. K.; Yoon, D.; Hwang, J.; Kim, S. M.; Kim, J. A Route to Synthesis Molybdenum Disulfide-Reduced Graphene Oxide (MoS2-RGO) Composites Using Supercritical Methanol and their Enhanced Electrochemical Performance for Li-Ion Batteries. J. Power Sources 2016, 309, 202−211. (10) Luo, Y.; Zhang, Y.; Zhao, Y.; Fang, X.; Ren, J.; Weng, W.; Jiang, Y.; Sun, H.; Wang, B.; Cheng, X.; Peng, H. Aligned Carbon Nanotube/Molybdenum Disulfide Hybrids for Effective Fibrous Supercapacitors and Lithium Ion Batteries. J. Mater. Chem. A 2015, 3, 17553−17557. (11) Liu, Y.; He, X.; Hanlon, D.; Harvey, A.; Khan, U.; Li, Y.; Coleman, J. N. Electrical, Mechanical, and Capacity Percolation Leads to High-Performance MoS2/Nanotube Composite Lithium Ion Battery Electrodes. ACS Nano 2016, 10, 5980−5990. (12) Jiang, H.; Ren, D.; Wang, H.; Hu, Y.; Guo, S.; Yuan, H.; Hu, P.; Zhang, L.; Li, C. 2D Monolayer MoS2-Carbon Interoverlapped Superstructure: Engineering Ideal Atomic Interface for Lithium Ion Storage. Adv. Mater. 2015, 27, 3687−3695. (13) Chen, C.; Feng, Z.; Feng, Y.; Yue, Y.; Qin, C.; Zhang, D.; Feng, W. Large-Scale Synthesis of a Uniform Film of Bilayer MoS2 on Graphene for 2D Heterostructure Phototransistors. ACS Appl. Mater. Interfaces 2016, 8, 19004−19011. (14) Zhang, L.; Fan, W.; Tjiu, W. W.; Liu, T. 3D Porous Hybrids of Defect-Rich MoS2/Graphene Nanosheets with Excellent Electrochemical Performance as Anode Materials for Lithium Ion Batteries. RSC Adv. 2015, 5, 34777−34787. (15) Pekker, S.; Salvetat, J. P.; Jakab, E.; Bonard, J. M.; Forró, L. Hydrogenation of Carbon Nanotubes and Graphite in Liquid Ammonia. J. Phys. Chem. B 2001, 105, 7938−7943. (16) Vishnyakova, E.; Brinson, B. E.; Alemany, L. B.; Verma, M.; Billups, W. E. Structural Characteristics and Properties of a New Graphitic-Based Material. Chem. - Eur. J. 2016, 22, 1452−1460. (17) Liang, F.; Sadana, A. K.; Peera, A.; Chattopadhyay, J.; Gu, Z.; Hauge, R. H.; Billups, W. E. A Convenient Route to Functionalized Carbon Nanotubes. Nano Lett. 2004, 4, 1257−1260.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.7b00248. Materials and methods; SEM and TEM images of fgraphene, MoS2 nanospheres, and MoS2@f-graphene; XPS spectra of pure MoS2 and MoS2@f-graphene; charge/discharge cycling performance of the MoS2@fgraphene electrodes with a high loading mass (PDF)

■

REFERENCES

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Jia Huang: 0000-0002-2873-7704 Author Contributions

The manuscript was written with contributions from all of the authors. All authors have given approval to the final version of the manuscript. Funding

Science & Techn ology Foundat ion o f Shangh ai (14JC1492600) Science & Technology Foundation of Shenzhen (JCYJ201419122040621) Fundamental Research Funds for the Central Universities The 1000 Youth Talent Plan Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors thank the Characterization and Testing Center of the School of Materials and Engineering at Tongji University. This work was supported by the Science & Technology Foundation of Shanghai (14JC1492600), the Science & Technology Foundation of Shenzhen F


Letter

ACS Applied Materials & Interfaces (18) Feng, L.; Liu, Y.; Tang, X.; Piao, Y.; Chen, S.; Deng, S.; Xie, S.; Wang, Y.; Zheng, L. Propagative Exfoliation of High Quality Graphene. Chem. Mater. 2013, 25, 4487−4496. (19) Bertrand, P. A. Surface-Phonon Dispersion of MoS2. Phys. Rev. B: Condens. Matter Mater. Phys. 1991, 44, 5745−5749. (20) Li, H.; Zhang, Q.; Yap, C. C. R.; Tay, B. K.; Edwin, T. H. T.; Olivier, A.; Baillargeat, D. From Bulk to Monolayer MoS2: Evolution of Raman Scattering. Adv. Funct. Mater. 2012, 22, 1385−1390. (21) Lee, W. S. V.; Peng, E.; Loh, T. A. J.; Huang, X.; Xue, J. M. Fewlayer MoS2-Anchored Graphene Aerogel Paper for Free-Standing Electrode Materials. Nanoscale 2016, 8, 8042−8047. (22) 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. (23) Li, H.; Yang, X.; Wang, X.; He, Y.; Ye, F.; Liu, M.; Zhang, Y. A Dual-Spatially-Confined Reservoir by Packing Micropores within Dense Graphene for Long-Life Lithium/Sulfur Batteries. Nanoscale 2016, 8, 2395−2402. (24) Sun, Z.; Yao, Y.; Wang, J.; Song, X.; Zhang, P.; Zhao, L.; Gao, L. High Rate Lithium-Ion Batteries from Hybrid Hollow Spheres with a Few-Layered MoS2-Entrapped Carbon Sheath Synthesized by a Spaceconfined Reaction. J. Mater. Chem. A 2016, 4, 10425−10434. (25) Benavente, E.; Santa Ana, M. A.; Mendizábal, F.; González, G. Intercalation Chemistry of Molybdenum Disulfide. Coord. Chem. Rev. 2002, 224, 87−109. (26) Oakes, L.; Carter, R.; Hanken, T.; Cohn, A. P.; Share, K.; Schmidt, B.; Pint, C. L. Interface Strain in Vertically Stacked TwoDimensional Heterostructured Carbon-MoS2 Nanosheets Controls Electrochemical Reactivity. Nat. Commun. 2016, 7, 11796. (27) Fu, W.; Du, F. H.; Su, J.; Li, X. H.; Wei, X.; Ye, T. N.; Wang, K. X.; Chen, J. S. In situ Catalytic Growth of Large-Area Multilayered Graphene/MoS2 Heterostructures. Sci. Rep. 2014, 4, 4673. (28) Fang, X.; Yu, X.; Liao, S.; Shi, Y.; Hu, Y.; Wang, Z.; Stucky, G. D.; Chen, L. Lithium Storage Performance in Ordered Mesoporous MoS2 Electrode Material. Microporous Mesoporous Mater. 2012, 151, 418−423. (29) Wang, J.; Zhou, M.; Tan, G.; Chen, S.; Wu, F.; Lu, J.; Amine, K. Encapsulating Micro-Nano Si/SiOx into Conjugated Nitrogen-Doped Carbon as Binder-Free Monolithic Anodes for Advanced Lithium Ion Batteries. Nanoscale 2015, 7, 8023−34.

G


Facile Synthesis of a MoS2 and Functionalized Graphene

Recommend Documents