Journal of Materials Chemistry A
View Article Online PAPER View Journal | View Issue
Fe3O4 quantum dot decorated MoS2 nanosheet arrays on graphite paper as free-standing sodium- Cite this: J. Mater. Chem. A,2017,5, 9122 ion battery anodes†
Dezhi Kong,ab Chuanwei Cheng,*a Ye Wang,*b Zhixiang Huang,b Bo Liu,b Yew Von Lim,b Qi Geb and Hui Ying Yang *b
A novel composite consisting of vertical ultrathin MoS2 nanosheet arrays and Fe3O4 quantum dots (QDs) grown on graphite paper (GP) as a high-performance anode material for sodium-ion batteries (SIBs) has been synthesized via a facile two-step hydrothermal method. Owing to the high reversible capacity
provided by the MoS2 nanosheets and the superior high rate performance offered by Fe3O4 QDs,
superior cycling and rate performances are achieved by Fe3O4@MoS2-GP anodes during the subsequent electrochemical tests, delivering 468 and 231 mA h g 1 at current densities of 100 and 3200 mA g 1, respectively, as well as retaining 72.5% of their original capacitance at a current density of 100 mA g 1 after 300 cycles. The excellent electrochemical performance resulted from the interconnected
nanosheets of MoS2 providing flexible substrates for the nanoparticle decoration and accommodating Received 7th February 2017 the volume changes of uniformly distributed Fe O QDs during the cycling process. Moreover, Fe O Accepted 5th April 2017 3 4 3 4 QDs primarily act as spacers to stabilize the composite structure, making the active surfaces of MoS2 DOI: 10.1039/c7ta01172e nanosheets accessible for electrolyte penetration during charge–discharge processes, which maximally
rsc.li/materials-a utilized electrochemically active MoS2 nanosheets and Fe3O4 QDs for sodium-ion batteries.
atom layers (S–Mo–S) stacked together via van der Waals 1. Introduction 21 interactions. The interlayered space between the MoS2 layers Sodium-ion batteries (SIBs) have attracted great interest in is 0.62 nm, which is a kind of suitable host material for Na+ 22,23 recent years because of the natural abundance and low cost of insertion and extraction. However, owing to their large Published on 05 April 2017. Downloaded by SUSTech 3/31/2020 4:06:33 AM. sodium, as well as its suitable redox potential (E(Na/Na+) ¼ surface energy, these neighboring 2D layers are inclined to 2.71 V vs. the standard hydrogen electrode).1–5 Nevertheless, aggregate or restack together by van der Waals attraction, the larger ionic radius of Na+ (1.02) than Li+ (0.76) makes it leading to fast capacity fading and serious volume variation 24 more difficult to nd appropriate electrode materials to during electrochemical cycles. Meanwhile, another drawback 6,7 25,26 accommodate the sodium ions. Thus, one main strategy to of MoS2 is the poor electronic/ionic conductivity. To over- improve the electrochemical performance of SIBs is to nd come these issues, one effective approach to enhance the elec- suitable sodium-ion insertion electrode materials, especially trochemical performance of MoS2 or MoS2-based composites is anode materials with an expanded interlayered structure and/or design of nanostructured MoS2 and using carbonaceous mate- 27,28 porous structure.8–10 rials as the conductive matrix. On the other hand, decorating Until now, the investigated anode materials for sodium-ion the MoS2 nanosheet surface with carbon or metal oxides acting batteries include carbon based materials,11–13 alloy/dealloy as a spacer layer can effectively prevent the structural degrada- materials,14–16 and transition metal oxides/suldes/phosphides/ tion, as well as formation of a stable SEI layer because of the 17–20 ff 29–32 nitrides. Among them, molybdenum sulde (MoS2) has unexpected interface e ects. a similar structure to graphene, which is composed of three Herein, we report a cost-effective and simple strategy to design and fabricate 3D Fe3O4 quantum dot decorated vertical
MoS2 nanosheet arrays grown on a GP substrate as a binder free aShanghai Key Laboratory of Special Articial Microstructure Materials and electrode for sodium-ion batteries. In such composite design, Technology, School of Physics Science and Engineering, Tongji University, Shanghai the Fe3O4 QDs act as a spacer layer to segregate the neighboring 200092, P. R. China. E-mail: [email protected] MoS2 nanosheets and allow the electrolyte penetrating the bPillar of Engineering Product Development, Singapore University of Technology and active surface of MoS2 thereby preventing the structural degra- Design, 8 Somapah Road, Singapore 487372, Singapore. E-mail: [email protected]. dation during the charging/discharging process. In the mean- sg; [email protected] † Electronic supplementary information (ESI) available. See DOI: time, the network-like MoS2 nanosheets with good mechanical 10.1039/c7ta01172e exibility provide ideal substrates for the Fe3O4 QD loading,
9122 | J. Mater. Chem. A,2017,5,9122–9131 This journal is © The Royal Society of Chemistry 2017 View Article Online Paper Journal of Materials Chemistry A
which can accommodate the volume change and prevent the reference electrode. The positive and negative electrodes were particle aggregation. In addition, the graphite paper substrates electronically separated by glass microber (Whatman) satu- are advantageous in terms of high conductivity, exibility and rated with electrolyte. The electrolyte solution was 1 M NaClO4 lightweight for the current collector, which is also benecial for dissolved in a mixture of ethylene carbonate (EC) and propylene
the performance. As a result, the as-fabricated Fe3O4@MoS2-GP carbonate (PC) with a volume ratio of 1 : 1, in which 5 vol% electrode exhibits a high reversible capacity and superior uoroethylene carbonate (FEC) was added as the electrolyte
cycling life and rate capability in contrast to that of MoS2-GP, additive. The charge–discharge measurements were performed
arising from the synergistic effect between the Fe3O4 QDs and at different current densities in the voltage range from 0.01 to + MoS2 nanosheets. 3.0 V versus Na /Na using a computer-controlled Neware Battery Testing system. Cyclic voltammetry (CV) was conducted by using a CHI 660C electro-chemical workstation between 0.01 2. Experimental section and 3.0 V versus Na+/Na with a scan rate of 0.1 mV s 1. The Synthesis of MoS nanosheets 2 electrochemical impedance spectroscopy (EIS) measurements
Self-supported MoS2 nanosheet arrays on graphite paper (GP) were carried out with an electrochemical workstation in the were fabricated using a modied hydrothermal growth frequency range from 100 kHz to 10 mHz under an open circuit method.33 In a typical process: rst, the GP substrate was treated potential. 2 by O2 plasma for 300 s. Then, one piece of 2.0 5.0 cm pre- treated GP substrate was immersed into a mixed solution con- taining 40 mL of DI water, 150 mg of sodium molybdate and 200 3. Results and discussion mg of thiourea, sealed in a Teon-lined stainless steel autoclave (50 mL) and maintained at 200 C for 18 h. A er that, the GP The fabrication processes of Fe3O4 quantum dot decorated 2 substrate covered with MoS2 nanosheets ( 0.5 mg cm ) was MoS2 nanosheet arrays on graphite paper are schematically washed with deionized water several times and nally dried at depicted in Fig. 1a. The whole synthetic process mainly involves 80 C overnight. three steps, i.e., (i) hydrothermal growth of MoS2 nanosheet arrays on graphite paper; (ii) forming FeOOH precursors on the Synthesis of Fe O @MoS composite 3 4 2 MoS2 nanosheets through a low temperature hydrolysis process; (iii) thermal treatment for transforming the FeOOH into crys- The Fe3O4 QDs on MoS2 nanosheets were fabricated by using a facile low-temperature hydrolysis process. In a typical proce- talline Fe3O4 quantum dots. The corresponding optical images ff dure, the MoS -coated graphite papers were immersed into 30 of the as-obtained products at di erent stages are provided in 2 † mM of Fe(NO ) $9H O aqueous solution for different times Fig. S1. As shown in Fig. 1b, the Fe3O4@MoS2-GP nano- 3 3 2 (such as 2 h, 5 h and 10 h) at 50 C to convert the Fe3+ into architecture delivers excellent exibility, and can be randomly † FeOOH. Then, the samples were washed several times with bent without damage. Fig. 1c and S2 schematically illustrates distilled water and ethanol, and then dried in a vacuum oven. the crystal structures of MoS2 nanosheets with (110) and (001) crystal planes, respectively, and the interlayer spacing of 0.65
Published on 05 April 2017. Downloaded by SUSTech 3/31/2020 4:06:33 AM. Finally, the as-obtained samples were annealed in an Ar atmo- sphere at 400 C for 2 h in order to transform the FeOOH into nm also matches well with the distance between the MoS2 layers. Meanwhile, the formation mechanism of the Fe3O4@- crystalline Fe3O4 quantum dots. MoS2 nanostructure is shown in Fig. S2.† – Characterization Fig. 2a c show the SEM images of the as-fabricated MoS2 nanosheet arrays on graphite paper. It can be seen that the The morphology was analyzed by using a eld emission scan- entire surface of the GP is uniformly covered with densely ning electron microscope (FESEM, Zeiss Supra 55VP). Trans- packed ultrathin graphene-like MoS2 nanosheet arrays. The mission electron microscopy (TEM) high-resolution TEM high-magnication view in Fig. 3c further reveals that the iso- ff images, selected area electron di raction (SAED) patterns, and lated nanosheets are interconnected with each other with energy X-ray dispersive (EDX) mapping images were collected several open voids. The cross-sectional view inset of Fig. 2c on a JEOL 100CX instrument, using a 300 kV accelerating indicates that the thickness of the MoS2 nanosheet arrays is voltage. The crystal structure and phase composition of the as- 2.5 mm. The detailed structures of the MoS nanosheets are ff 2 prepared materials were characterized by X-ray di raction further characterized by TEM and HR-TEM. The TEM image in a (XRD, Siemens D5000) using Cu K radiation with a scanning Fig. 2d shows that the thickness of sheet-like MoS is 5–10 nm, 1 2 step of 0.02 s . Raman spectroscopy was carried out using corresponding to 8–13 layers of S–Mo–S with an interlayer a WITEC CRM200 Raman system equipped with a 532 nm laser spacing of about 0.64 nm. The measured lattice spacing of 0.27 source and 100 objective lens. nm in Fig. 2f is consistent with the d spacing of (100) planes of hexagonal MoS .34 The selected area electron diffraction (SAED) Electrochemical measurements 2 pattern (inset of Fig. 2f) shows clear diffraction rings, indicating ff The CR2032-type coin cells were assembled in an argon- lled the polycrystalline nature of MoS2. These di raction rings can
glovebox (UniLab, Mbraun, Germany). The as-obtained Fe3- be well indexed to the (002), (100), (103), and (110) planes of 2 35 O4@MoS2-GP was cut into 0.6 0.6 cm and directly used as MoS2. It is worth noting that our general fabrication strategy
a self-supported electrode. Na foil was used as the counter and for MoS2 nanosheet arrays can be extended to any substrates
This journal is © The Royal Society of Chemistry 2017 J. Mater. Chem. A,2017,5,9122–9131 | 9123 View Article Online Journal of Materials Chemistry A Paper
Fig. 1 (a) Schematic illustration of the fabrication process for the Fe3O4@MoS2 composite on graphite paper; (b) photographs of a flexible GP 2 substrate, MoS2-GP and Fe3O4@MoS2-GP electrodes (3.0 1.5 cm ); (c) the crystal structures of MoS2 with the (110) crystal plane.
such as graphite paper, carbon cloth and stainless steel foil, as dispersed Fe3O4 QDs are well distributed on both surfaces of
demonstrated in Fig. S3.† each isolated MoS2 nanosheet without any aggregation, which is
Aer the Fe3O4 QD decoration, the morphology of the MoS2 favoring the electrode/electrolyte interactions. From the TEM
nanosheet arrays had not changed much, as shown in Fig. 3a image observation in Fig. 3d and e, the size of the Fe3O4 can be and b. From a closer view in Fig. 3b, one can see that the determined in the range of 5–10 nm. The HRTEM image in
surfaces of the MoS2 nanosheets are very rough, indicating the Fig. 3f shows clear lattice fringes for the Fe3O4 QDs, indicating
successful decoration of Fe3O4 QDs. Noting that the spatially a high degree of crystallinity. The crystal lattice with a spacing of Published on 05 April 2017. Downloaded by SUSTech 3/31/2020 4:06:33 AM.
Fig. 2 (a and b) Low- and (c) high-magnification SEM images of MoS2 nanosheets; (d) TEM images of MoS2 nanosheets; (e and f) high resolution TEM image of MoS2 nanosheets. Inset: SAED patterns of MoS2 nanosheets.
9124 | J. Mater. Chem. A,2017,5,9122–9131 This journal is © The Royal Society of Chemistry 2017 View Article Online Paper Journal of Materials Chemistry A
Fig. 3 (a–c) SEM images, (d–f) TEM images, and (g–i) EDS mappings with the corresponding SEM image of the Fe3O4@MoS2-GP composite. The insets of (f) shows the particle size distribution of the Fe3O4 QDs.
36 0.25 nm corresponds to the (311) plane of Fe3O4. As shown in Moreover, the diffraction peaks at present 14.1 , 33.4 , 39.8 , the inset in Fig. 3f, the average particle size of the Fe3O4 QDs is and 58.8 in the Fe3O4@MoS2-GP and MoS2-GP samples corre- 5 nm, as evidenced by the corresponding size distribution spond to the (002), (100), (103), and (110) planes of MoS2 (JCPDS analysis. Moreover, the EDS elemental mapping images of Mo, no. 37-1429).41 The two strong peaks marked by “#” belong to
S, Fe and O for a typical Fe3O4@MoS2-GP composite, as shown the GP substrate.
in Fig. 3h, demonstrate the uniform coating of Fe3O4 on the The sizes and mass loading of the Fe3O4 QDs can be well
surface of MoS2 nanosheets. The EDS spectrum result shown in controlled by changing the reaction times. Fig. 5a–h show the Published on 05 April 2017. Downloaded by SUSTech 3/31/2020 4:06:33 AM. Fig. 3i is consistent with that of the SEM elemental mapping SEM images of the Fe3O4@MoS2 hybrids with varied reaction and further veries the uniform presence of Fe, O, Mo, and S times from 0–10 h. It can be found that the sizes and loading
(with a Fe/O and Mo/S molar ratio of 4/3 and 2/1, respectively). density of the Fe3O4 QDs increase accordingly with the incre-
In addition, the EDS elemental mapping and spectral images of ment of times. To optimize the mass loading of the Fe3O4 QDs, ff the pure MoS2-GP were also observed for comparison, as shown three types of Fe3O4@MoS2 with di erent reaction times in Fig. S4.† (marked as Fe3O4@MoS2-GP-2, Fe3O4@MoS2-GP-5, and Fe3-
The phase and structures of the as-prepared MoS2 nano- O4@MoS2-GP-10) were selected for sodium ion battery anodes.
sheets and Fe3O4@MoS2 composites on the GP substrate were The cycling tests shown in Fig. S5† indicate that the Fe3O4@-
veried by Raman spectroscopy and powder X-ray diffraction MoS2-GP-5 electrode presents the best overall electrochemical
(XRD). The Raman spectra shown in Fig. 4a present two char- performance. This might be due to the fact that Fe3O4 QDs with acteristic peaks of the GP substrate, observed at 1350 and 1580 a larger size and thicker shell would hinder the electrolyte from 1 cm corresponding to the D and G bands, respectively. Here, interacting with the MoS2 nanosheets, leading to the structural the Raman intensity of the G band is much higher than that of collapse, as shown Fig. S6.† the 2D band, which is consistent with the multilayer properties To evaluate the mechanism of the electrochemical properties 37 of GP. To observe from the enlarged area, the Fe3O4@MoS2-GP of sodium storage in the Fe3O4@MoS2-GP electrode, the initial composites have two obvious peaks at 383 cm 1 and 405 cm 1, ten CV curves were recorded in the potential range of 3.0 to 0.01 1 1 + 1 which correspond to the E2g and Ag Raman modes of MoS2, V(vs. Na/Na ) at a slow scan rate of 0.1 mV s , as shown in respectively.38 Meanwhile, it is worth noting that the phonon Fig. 6a. During the rst cycle, three reduction peaks at 0.8, 0.6 1 bands at around 670, 533 and 309 cm can be ascribed to A1g, and 0.01 V and the three corresponding oxidation peaks/
T2g and Eg modes, respectively, which are the characteristic shoulder at 0.5, 1.8 and 2.5 V can be observed. The sodiation 39 + Raman signature of Fe3O4. As shown in Fig. 4b, the XRD peak at around 0.8 V is attributed to the intercalation of Na into patterns of the Fe3O4@MoS2-GP composites are in accordance the interlayer of MoS2, and the peak at around 0.6 V is due to the 40 with those of magnetite-type Fe3O4 (JCPDS card no. 19-0629). conversion reaction, while the band at potential below 0.01 V is
This journal is © The Royal Society of Chemistry 2017 J. Mater. Chem. A,2017,5,9122–9131 | 9125 View Article Online Journal of Materials Chemistry A Paper Published on 05 April 2017. Downloaded by SUSTech 3/31/2020 4:06:33 AM.
Fig. 4 Raman spectra (a) and XRD patterns (b) of the GP substrate, MoS2-GP and Fe3O4@MoS2-GP composites.
+ ascribed to the Na storage in the interface between Na2S and desodiation process of the Fe3O4@MoS2-GP hybrids. For Mo, consistent with literature reports.42,43 In addition, the broad comparison, the cyclic voltammetry (CV) curves of the pristine
peak centered at 0.75 V in the rst cathodic scan can be GP substrate, MoS2-GP, and Fe3O4@MoS2-GP electrodes at attributed to the structural transition induced by intercalation a scan rate of 0.1 mV s 1 are shown in Fig. S7a and b.† It can be
of the sodium into the crystalline Fe3O4. The second cathodic found that the capacitance contribution from the GP substrate peak at 0.05 V should correspond to the complete reduction of is negligible. The current density and enclosed CV curve area of 2+ 3+ 0 Fe /Fe to Fe and the Na2O, which was formed by conversion the Fe3O4@MoS2-GP electrode are much larger than that of the 44,45 reactions. In the anodic process, the wide peak observed at MoS2-GP electrode, arising from the increased activated sites 0 1.90 V corresponds to the reoxidation process of Fe to Fe3O4 and hybrid structural effect from the small size Fe3O4 QDs and 46 and decomposition of Na2O. The intensity decrease of the ultrathin MoS2 nanosheets. As mentioned above, the multi-step
peak at 0.6 V in the following cycles suggests that the SEI lm is sodium insertion/extraction process taking place at the Fe3-
formed on the electrode surface at this potential, which will O4@MoS2-GP electrode could be described by the following lead to irreversible capacity loss and low coulombic efficiency in reactions:45,48–50 the rst cycle.47 In the second sodiation, the reductive peak at + 0.8 V shis to a higher potential of 1.4 V, and the intensity of MoS2 + xNa + xe / NaxMoS2 (1) peaks at 0.6 V and 0.01 V are reduced; while the oxidation peaks Na MoS +(4 x)Na+ +(4 x)e 4 2Na S+Mo at 2.5 V are slightly increased. Aer the h cycle, the CV peaks x 2 2 (2) are stable, indicating good reversibility and a stable sodiation/ + Fe3O4 + 2Na +2e / Na2(Fe3O4) (3)
9126 | J. Mater. Chem. A,2017,5,9122–9131 This journal is © The Royal Society of Chemistry 2017 View Article Online Paper Journal of Materials Chemistry A Published on 05 April 2017. Downloaded by SUSTech 3/31/2020 4:06:33 AM.
Fig. 5 Morphologies of the Fe3O4@MoS2-GP composites during the second hydrothermal process at various reaction stages by setting the reaction time to (a and b) 0 h, (c and d) 2 h, (e and f) 5 h; (g and h) 10 h. (i) Proposed mechanism for the effect of the reaction time on the morphology construction.
+ 0 Na2(Fe3O4) + 6Na +6e 4 3Fe + 4Na2O (4) loss is most likely due to the irreversible reactions by the formation of the solid electrolyte interface (SEI) layer, as seen also from the shape difference between the discharge voltage The galvanostatic charge/discharge proles of the as- proles of the rst and second cycle. Moreover, the potential prepared Fe3O4@MoS2-GP electrode at a current density of 100 plateaus at 1.8 V and 0.8 V are also in agreement with the two mA g 1 are displayed in Fig. 6b. In agreement with the CV peaks of the CV curves in Fig. 6a. For comparison, the voltage- – – curves, three voltage plateaus at around 0.85 1.2 V, 0.6 0.85 and capacity trace of the bare MoS2 electrode was measured and is below 0.3 V can be observed in the discharge process of the rst shown in Fig. S7c.† cycle. The small plateau at 1.3 V during the rst discharge The cycling performances of the Fe3O4@MoS2-GP and MoS2- reects the formation of the solid electrolyte interface (SEI) lm GP electrodes are shown in Fig. 6c. It can be seen that the
and contributes to the irreversible capacity thus lowering the Fe3O4@MoS2-GP can deliver a discharge (sodiation) capacity of efficiency in the rst cycle. The second potential plateau at 0.6 388 mA h g 1 aer 300 cycles at a current density of 100 mA g 1, 1 V corresponds to the conversion of MoS2 to metallic Mo and which is much higher than that of bare MoS2-GP (76.8 mA h g ) Na2S. The Fe3O4@MoS2-GP electrode delivered initial discharge under the same conditions. In order to achieve high power and charge capacities of 822.1 and 496.8 mA h g 1, respectively, densities, a high-rate capability is essential. Fig. 6d shows the ffi 1 delivering a coulombic e ciency of 60.4%. The calculated high-rate (100–3200 mA g ) capability properties of the Fe3-
capacities are based on the weight of Fe3O4@MoS2. The capacity O4@MoS2-GP and MoS2-GP electrodes. Evidently, the
This journal is © The Royal Society of Chemistry 2017 J. Mater. Chem. A,2017,5,9122–9131 | 9127 View Article Online Journal of Materials Chemistry A Paper Published on 05 April 2017. Downloaded by SUSTech 3/31/2020 4:06:33 AM.
Fig. 6 (a) Representative CV curves of an electrode based on the Fe3O4@MoS2-GP composite obtained in the voltage range of 0 to 3.0 V (vs. Na/ Na+) and a potential scan rate of 0.1 mV s 1; (b) voltage profiles plotted for the first, second, third, 5th,8th,10th,20th and 50th cycles of the 1 Fe3O4@MoS2-GP composite electrode at a current density of 100 mA g ; (c) cycling performance and the corresponding coulombic efficiencies 1 of the Fe3O4@MoS2-GP composite electrode at 100 mA g and the cycling performance of the MoS2-GP electrode; (d) rate-performance of the Fe3O4@MoS2-GP composite electrode; (e) charge–discharge curves of the Fe3O4@MoS2-GP composite electrode at different current densities; (f) Nyquist plots before long cycling and the corresponding equivalent circuit model of the Fe3O4@MoS2-GP, MoS2-GP and GP cathode. The inset shows the fitted equivalent circuit model.
Fe3O4@MoS2-GP electrode shows a stable high-rate prole with of the designed composite electrode. The capacity and cycling 1 1 specic capacities ranging from 468 mA h g at 100 mA g to performance of the Fe3O4@MoS2-GP electrodes in our case are 1 1 232 mA h g at 3200 mA g . These values are consistently superior to most of the previous reports for MoS2 nano-
higher than those of the MoS2-GP counterpart (from 264 mA h structures and MoS2-based composite electrodes, as summa- g 1 at 100 mA g 1 to 56 mA h g 1 at 3200 mA g 1), as well as rized in Table S1 in the ESI.† 51,52 other MoS2 based composites. In addition, for the Fe3O4@- To understand the underlying mechanism of the perfor-
MoS2-GP electrode, the capacity retention of 38.7% is main- mance improvement, electrochemical impedance spectroscopy tained as the charge–discharge rate increases from 100 mA g 1 (EIS), SEM, ex situ TEM and Raman measurements were per- to 3200 mA g 1, suggesting its excellent rate capability. Fig. 6e formed. Prior to the EIS tests, the cells were run over 3 cycles.
shows the charge–discharge voltage proles of the Fe3O4@- The GP substrate, pristine MoS2 electrode and Fe3O4@MoS2-GP – MoS2-GP electrode in the voltage window of 0.01 3.0 V at electrode's Nyquist plots taken in the frequency range of 0.01 Hz ff di erent current densities. The Fe3O4@MoS2-GP electrode to 100 kHz at open circuit potential are shown in Fig. 6f. The exhibits very stable charge–discharge voltage proles when the Nyquist plots of these electrodes consist of a single depressed current density is increased from 100 to 3200 mA g 1, which semicircle in the high-medium frequency region and an further indicates the enviable rate capability and high stability inclined line at the low frequency, respectively. As shown in the
9128 | J. Mater. Chem. A,2017,5,9122–9131 This journal is © The Royal Society of Chemistry 2017 View Article Online Paper Journal of Materials Chemistry A
inset of Fig. 6f, the elements in the equivalent circuit include worse than those aer 3 cycles. This impedance evolution – the ohmic resistance of the electrolyte and cell components (Re), further demonstrates that long-time charge discharge surface lm resistance (Rsf), charge-transfer resistance at the processes have not damaged the Fe3O4@MoS2-GP composite
interface between the electrode and electrolyte (Rct), a constant electrode. Meanwhile, the morphologies of the nanosheets from phase element (CPEsf+dl, surface lm (sf), double layer (dl)) used the MoS2-GP and Fe3O4@MoS2-GP electrodes aer 300 cycles instead of pure capacitance due to the depressed semicircle, were checked by SEM and EDS. It is observed that the core–shell 53 Warburg impedance (ZW), and intercalation capacitance (Cint). crossed nanosheet architecture is well preserved without large
By tting the EIS spectra with this equivalent circuit, the value deformation (Fig. S8c, d and S9†), whereas for the bare MoS2-GP
of Re is 10–15 U for the three samples, indicating that the cells electrode, the nanosheets tend to aggregate and expand have been properly fabricated and tested under the same (Fig. S8a and b†). Moreover, the morphology and structure of
conditions. Due to the single semicircle observed, the imped- the Fe3O4@MoS2-GP composite were further investigated by ance can be ascribed to the combination of the surface lm and TEM and Raman aer 100 cycles and are displayed in Fig. S10.†
charge-transfer resistance R(sf+ct). The tting parameter of R(sf+ct) As can be seen from Fig. S10a,† the Fe3O4@MoS2 electrode
is much lower for the Fe3O4@MoS2-GP electrode (121.8 U) almost maintains its original appearance, in which the MoS2
compared to that of the MoS2-GP electrode (248.6 U), but is nanosheets were still covered with homogeneous Fe3O4 QDs. larger than that of the GP electrode (60.3 U), which means that Meanwhile, a thin stable SEI layer ( 15 nm) is reasonably
the Fe3O4@MoS2-GP electrode has a faster charge-transfer formed on the surface of the Fe3O4@MoS2 electrode. In fact, process than the MoS2-GP electrode. A er 300 cycles, the Rct this conclusion is also supported by the Raman result. As shown U † slightly increases from 121.8 to 146.4 , as shown in Fig. 7a, in Fig. S10b, the peaks of MoS2 and Fe3O4 could hardly be which may be due to the stabilization of the SEI lm and observed aer 300 cycles, which indirectly indicates the
a relatively favorable diffusion of lithium ions and electrons. formation of stable SEI layers during cycling in the Fe3O4@- 0 1/2 Fig. 7b show the Z –u (u ¼ 2pf) curves in the low frequency MoS2 electrode. region, and the low slope indicates good sodium-ion kinetics in The excellent electrochemical performance of the hybrid 54 the electrode materials. This clearly shows that the sodium ion Fe3O4@MoS2-GP as the anode for SIBs might be due to the
kinetics of the Fe3O4@MoS2-GP electrode aer 300 cycles were synergistic effect between the Fe3O4 QDs and the network-like Published on 05 April 2017. Downloaded by SUSTech 3/31/2020 4:06:33 AM.
Fig. 7 (a) Nyquist plots of the Fe3O4@MoS2-GP electrode after 3 cycles and after 300 cycles, respectively; (b) linear fits in the low frequency region of the Nyquist plots of the Fe3O4@MoS2-GP electrode after 3 cycles and after 300 cycles, respectively; (c) synergistic electrochemical characteristics of the hybrid Fe3O4@MoS2-GP composite electrode.
This journal is © The Royal Society of Chemistry 2017 J. Mater. Chem. A,2017,5,9122–9131 | 9129 View Article Online Journal of Materials Chemistry A Paper
MoS2 nanosheets, as illustrated in Fig. 7c. First, the vertically 6 N. Yabuuchi, K. Kubota, M. Dahbi and S. Komaba, Chem. 114 – orientated MoS2 nanosheet arrays provide substrates for the Rev., 2014, , 11636 11682. 28 Fe3O4 QD decoration, which can provide a large electrode/ 7 G. He, W. H. Kan and A. Manthiram, Chem. Mater., 2016, , electrolyte interface area, accommodate the volume change and 682–688.
prevent particle agglomeration of Fe3O4, resulting in high 8 Y. Wang, D. Z. Kong, W. H. Shi, B. Liu, G. J. Sim, Q. Ge and
reversible capacity. Second, the ultrasmall Fe3O4 QDs with size H. Y. Yang, Adv. Energy Mater., 2016, 6, 1601057. less than 5 nm can serve as spacers to form a stable SEI lm and 9 D. Z. Kong, C. W. Cheng, Y. Wang, B. Liu, Z. X. Huang and
hinder the restacking of adjacent MoS2 nanosheets, leading to H. Y. Yang, J. Mater. Chem. A, 2016, 4, 11800–11811. excellent structural integrity during the charge–discharge 10 D. L. Chao, C. R. Zhu, P. H. Yang, X. H. Xia, J. L. Liu, J. Wang, process and superior cycling stability. Third, the ultrasmall X. F. Fan, S. V. Savilov, J. Y. Lin, H. J. Fan and Z. X. Shen, Nat. ff 7 Fe3O4 QDs shorten the di usion path of sodium ions and Commun., 2016, , 12122. electrons which can effectively and quickly transfer between the 11 Y. Wang, C. Y. Wang, Y. J. Wang, H. K. Liu and Z. G. Huang,
Fe3O4 QDs and the current collector based on MoS2 nanosheets, ACS Appl. Mater. Interfaces, 2016, 8, 18860–18866. while the 3D porous structure with open spaces facilitates the 12 X. F. Luo, C. H. Yang, Y. Y. Peng, N. W. Pu, M. D. Ger, easy access and fast diffusion of the electrolytes, thereby C. T. Hsiehd and J. K. Chang, J. Mater. Chem. A, 2015, 3, enabling the hybrids possess superior rate capability. All these 10320–10326. merits would undoubtedly play an important role in improving 13Y.Wen,K.He,Y.J.Zhu,F.D.Han,Y.H.Xu,I.Matsuda,Y.Ishii, the electrochemical performance of the electrode materials. J. Cumings and C. S. Wang, Nat. Commun., 2014, 5, 4033. 14 L. Y. Hu, X. S. Zhu, Y. C. Du, Y. F. Li, X. S. Zhou and J. C. Bao, 4. Conclusions Chem. Mater., 2015, 27, 8138–8145. 15 M. He, M. Walter, K. V. Kravchyk, R. Erni, R. Widmer and
In summary, we have fabricated Fe3O4@MoS2-GP composites M. V. Kovalenko, Nanoscale, 2015, 7, 455–459.
with Fe3O4 QDs decorated on ultrathin MoS2 nanosheet arrays 16 J. Qian, X. Wu, Y. Cao, X. Ai and H. Yang, Angew. Chem., 2013, through a facile two-step hydrothermal method. The as-fabri- 125, 4731–4734.
cated Fe3O4@MoS2-GP composites were explored as an anode 17 Y. Jiang, M. Hu, D. Zhang, T. Yuan, W. Sun, B. Xu and for SIBs, which exhibited superior electrochemical storage M. Yan, Nano Energy, 2014, 5,60–66. performance in terms of capacity, cycling stability and rate 18 X. Q. Xie, Z. M. Ao, D. W. Su, J. Q. Zhang and G. X. Wang, Adv. capability. The signicantly improved performance can be Funct. Mater., 2015, 25, 1393–1403. ff attributed to the synergistic e ect between the Fe3O4 QDs with 19 F. P. Zhao, N. Han, W. J. Huang, J. J. Li, H. L. Ye, F. J. Chen high rate performance and MoS2 nanosheets offering high and Y. G. Li, J. Mater. Chem. A, 2015, 3, 21754–21759. capacity, leading to formation of a stable SEI lm and main- 20 Y. Zhong, X. H. Xia, F. Shi, J. Y. Zhan, J. P. Tu and H. J. Fan, taining the structural integrity of the composite during the Adv. Sci., 2016, 3, 1500286. charging/discharging process. Our results open new opportu- 21 C. Y. Zhao, X. Wang, J. H. Kong, J. M. Ang, P. S. Lee, Z. L. Liu 8 – nities for the design of MoS2 based anodes for high-perfor- and X. H. Lu, ACS Appl. Mater. Interfaces, 2016, , 2372 2379. Published on 05 April 2017. Downloaded by SUSTech 3/31/2020 4:06:33 AM. mance sodium ion batteries. 22 Y. L. Liang, H. D. Yoo, Y. F. Li, J. Shuai, H. A. Calderon, F. C. R. Hernandez, L. C. Grabow and Y. Yao, Nano Lett., Acknowledgements 2015, 15, 2194–2202. 23 Z. Hu, L. X. Wang, K. Zhang, J. B. Wang, F. Y. Cheng, This work is nancially supported by the 973 Program (Grant Z. L. Tao and J. Chen, Angew. Chem., Int. Ed., 2014, 53, no. 2013CB632701), the National Natural Science Foundation of 12794–12798. China (Grant no. 51202163) and SUTD Digital Manufacturing 24 Y. X. Wang, S. L. Chou, D. Wexler, H. K. Liu and S. X. Dou, and Design (DManD) Centre. A research grant from AFOSR Chem.–Eur. J., 2014, 20, 9607–9612. (grant number 15IOA029) is gratefully acknowledged. 25 T. S. Sahu and S. Mitra, Sci. Rep., 2015, 5, 12571. 26 Y. P. Liu, X. Y. He, D. Hanlon, A. Harvey, J. N. Coleman and References Y. G. Li, ACS Nano, 2016, 10, 8821–8828. 27 L. F. Jiang, B. H. Lin, X. M. Li, X. F. Song, H. Xia, L. Li and 1 J. Sun, H. W. Lee, M. Pasta, H. Yuan, G. Zheng, Y. Sun, Y. Li H. B. Zeng, ACS Appl. Mater. Interfaces, 2016, 8, 2680–2687. and Y. Cui, Nat. Nanotechnol., 2015, 10, 980–985. 28 Z. Z. Che, Y. F. Li, K. X. Chen and M. D. Wei, J. Power Sources, 2 P. Barpanda, G. Oyama, S. I. Nishimura, S. C. Chung and 2016, 331,50–57. A. Yamada, Nat. Commun., 2014, 5, 4358. 29 Y. Fang, Y. Y. Lv, F. Gong, A. A. Elzatahry, G. F. Zheng and 3 X. Q. Xie, T. Makaryan, M. Q. Zhao, K. L. Van Aken, Y. Gogotsi D. Y. Zhao, Adv. Mater., 2016, 28, 9385–9390. and G. X. Wang, Adv. Energy Mater., 2015, 6, 1502161. 30 B. Chen, E. Z. Liu, F. He, C. S. Shi, C. N. He, J. J. Li and 4 V. Palomares, M. Casas Cabanas, E. Castillo Martinez, N. Q. Zhao, Nano Energy, 2016, 26, 541–549. M. H. Han and T. Rojo, Energy Environ. Sci., 2013, 6, 2312– 31 Y. Chen, B. H. Song, X. S. Tang, L. Lu and J. M. Xue, Small, 2337. 2014, 10, 1536–1543. 5 Y. C. Liu, N. Zhang, L. F. Jiao, Z. L. Tao and J. Chen, Adv. 32 S. H. Choi and Y. C. Kang, ACS Appl. Mater. Interfaces, 2015, Funct. Mater., 2015, 25, 214–220. 7, 24694–24702.
9130 | J. Mater. Chem. A,2017,5,9122–9131 This journal is © The Royal Society of Chemistry 2017 View Article Online Paper Journal of Materials Chemistry A
33 X. Q. Xie, T. Makaryan, M. Q. Zhao, K. L. V. Aken, Y. Gogotsi 44 H. Liu, M. Q. Jia, Q. Z. Zhu, B. Cao, R. J. Chen, Y. Wang, and G. X. Wang, Adv. Energy Mater., 2016, 6, 1502161. F. Wu and B. Xu, ACS Appl. Mater. Interfaces, 2016, 8, 34 J. W. Zhou, J. Qin, N. Q. Zhao, C. S. Shi, E. Z. Liu, F. He, J. J. Li 26878–26885. and C. N. He, J. Mater. Chem. A, 2016, 4, 8734–8741. 45 S. Hariharan, K. Saravanan, V. Ramar and P. Balaya, Phys. 35 D. Z. Zhang, Y. Sun, P. Li and Y. Zhang, ACS Appl. Mater. Chem. Chem. Phys., 2013, 15, 2945–2953. Interfaces, 2016, 8, 14142–14149. 46 S. M. Oh, S. T. Myung, C. S. Yoon, J. Lu, J. Hassoun, 36 H. G. Wang, D. L. Ma, X. L. Huang, Y. Huang and B. Scrosati, K. Amine and Y. K. Sun, Nano Lett., 2014, 14, X. B. Zhang, Sci. Rep., 2012, 2, 701. 1620–1626. 37 L. G. Cancado, A. Jorio, E. H. Martins Ferreira, F. Stavale, 47S.Zhang,X.B.Yu,H.L.Yu,Y.J.Chen,P.Gao,C.Y.Liand C. A. Achete, R. B. Capaz, M. V. O. Moutinho, A. Lombardo, C. L. Zhu, ACS Appl. Mater. Interfaces, 2014, 6, 21880– T. S. Kulmala and A. C. Ferrari, Nano Lett., 2011, 11, 3190– 21885. 3196. 48 J. J. Wang, C. Luo, T. Gao, A. Langrock, A. C. Mignerey and 38 Y. Wang, Q. T. Qu, G. C. Li, T. Gao, F. Qian, J. Shao, W. J. Liu, C. S. Wang, Small, 2015, 11, 473–481. Q. Shi and H. H. Zheng, Small, 2016, 12, 6033–6041. 49 J. Y. Liao, B. D. Luna and A. Manthiram, J. Mater. Chem. A, 39 Y. Jiang, Z. J. Jiang, L. F. Yang, S. Cheng and M. L. Liu, J. 2016, 4, 801–806. Mater. Chem. A, 2015, 3, 11847–11856. 50 Y. Q. Fu, Q. L. Wei, X. Y. Wang, G. X. Zhang, H. B. Shu, 40 C. N. He, S. Wu, N. Q. Zhao, C. S. Shi, E. Z. Liu and J. J. Li, ACS X. K. Yang, A. C. Tavares and S. H. Sun, RSC Adv., 2016, 6, Nano, 2013, 7, 4459–4469. 16624–16633. 41 J. Y. Liao, B. D. Luna and A. Manthiram, J. Mater. Chem. A, 51 S. Hariharan, K. Saravanan, V. Ramar and P. Balaya, Phys. 2016, 4, 801–806. Chem. Chem. Phys., 2013, 15, 2945–2953. 42 D. W. Su, S. X. Dou and G. X. Wang, Adv. Energy Mater., 2015, 52 Y. Chen, B. H. Song, X. S. Tang, L. Lu and J. M. Xue, Small, 5, 1401205. 2014, 10, 1536–1543. 43 Z. Hu, L. X. Wang, K. Zhang, J. B. Wang, F. Y. Cheng, 53 J. Sun, H. W. Lee, M. Pasta, Y. M. Sun, W. Liu, Y. B. Li, Z. L. Tao and J. Chen, Angew. Chem., Int. Ed., 2014, 53, H. R. Lee, N. Liu and Y. Cui, Energy Storage Materials, 12794–12798. 2016, 4, 130–136. 54 S. H. Choi, N. K. You, J. K. Lee and Y. C. Kang, Adv. Funct. Mater., 2015, 25, 1780–1788. Published on 05 April 2017. Downloaded by SUSTech 3/31/2020 4:06:33 AM.
This journal is © The Royal Society of Chemistry 2017 J. Mater. Chem. A,2017,5,9122–9131 | 9131