Vertically Oxygen-Incorporated MoS2 Nanosheets Coated on Carbon

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Vertically Oxygen-Incorporated MoS2 Nanosheets Coated on Carbon Fibers for Sodium Ion Batteries Yaqiong Zhang, Huachao Tao, Tao Li, Shaolin Du, Jinhang Li, Yukun Zhang, and Xue-Lin Yang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b12079 • Publication Date (Web): 20 Sep 2018 Downloaded from http://pubs.acs.org on September 20, 2018

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ACS Applied Materials & Interfaces

Vertically Oxygen-Incorporated MoS2 Nanosheets Coated on Carbon Fibers for Sodium Ion Batteries Yaqiong Zhanga, Huachao Taoa,b*, Tao Lia,b, Shaolin Dua, Jinhang Lia, Yukun Zhanga, Xuelin Yanga,b* a

College of Materials and Chemical Engineering, China Three Gorges University 8 Daxue Road, Yichang, Hubei 443002, China

b

Collaborative Innovation Center for Microgrid of New Energy, Yichang, Hubei 443002, China E-mail: [email protected] (H. Tao); [email protected] (X. Yang)

Abstract Developing the high-performance anode with high reversible capacity, rate performance and great cycle stability is highly important for sodium ion batteries (SIBs). MoS2 has attracted extensive interest as anode for SIBs. Herein, the vertically oxygen-incorporated MoS2 nanosheets/carbon fibers are constructed via a facile hydrothermal method and then by a simple calcination in air. Oxygen incorporation in MoS2 can increase defect degree and expand interlayer spacing. Vertical MoS2 nanosheets array coated on carbon fibers not only can expose rich active sites and reduce the diffusion distance of Na+, but also improve the electronic conductivity and enhance structural stability. Meanwhile, interlayer expanded MoS2 can decrease Na+ diffusion resistance and increase accessible active sites for Na+. In this work, the electrode combining the oxygen-incorporated strategy with vertical MoS2 nanosheets integrated carbon fibers displays high specific capacities of 330 mAh g-1 over 100 cycles at a current density of 0.1 A g-1 together with excellent rate behavior as anode for SIBs. This strategy offers a helpful way for improving the electrochemical performance. Key words: sodium ion batteries; anode; MoS2; oxygen incorporation; vertical nanosheets array; 1

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carbon fibers; 1. Introduction In recent years, lithium ion batteries (LIBs) have been extended to renewable energy storage and conversion. However, the lack of lithium resources in the world comes to be an increasing issue.1, 2 Sodium ion batteries (SIBs) have drawn great attention because of their earth abundancy and available sodium resources and been considered as the appealing candidate for LIBs.3-7 In fact, the larger ionic radius of Na+ (1.02 Å) than that of Li+ (0.76 Å), which hinder the practical applications of SIBs due to the lack of appropriate anode materials to host Na+. Therefore, the commercial anode employed in lithium ion batteries, graphite, is not suitable as Na+ anode material for SIBs because of its small interlayer spacing of 0.335 nm.8 The repeated Na+ insertion/extraction in graphite electrode leads to low capacity because of the limited intercalating capability and the inferior cycling stability on account of the large volume expansion/contraction.9 So, there is an intense demand to find new and commercially available anode candidates of SIBs. Two-dimensionally layered-structured transitional metal dichalcogenides are believed as promising candidates for Na-ion batteries owing to their weak interlayer van der Waals forces, which can deliver the facile intercalation for sodium ions. MoS2 has a large interlayer distance of 0.62 nm, and a layered structure (S-Mo-S) sandwich layers, has been taken a great deal as anode material for LIBs and SIBs.10-17 However, the low electronic conductivity and high mechanical stress/strain of MoS2 during Na+ insertion/extraction cause to the cracking of the electrode materials and poor cycling performance.18-21 Moreover, the intrinsic instability leads to restack and loses its original microstructure during the discharge/charge process.22-25 To solve these factors, lots of efforts have been employed to improve the reversible capacity and cycling life, such as combination of MoS2 with carbon-based materials (MoS2/CNT,26 MoS2/carbon fibers27-29 and MoS2/porous carbon30), and expanding the interlayer spacing of MoS2.31-33 Moreover, defect-rich MoS2 exhibits improved electrochemical activity due to the increase of active sites.34-36 Vertical MoS2 nanosheets 2


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facilitate the permeation of electrolyte and fast Na ion transport. Therefore, vertical MoS2 nanosheets with expanded interlayer and rich defect are expected to obtain the high-performance electrode. Herein, we report vertically oxygen-incorporated MoS2 nanosheets coated on carbon fibers (OMSCF) electrodes, which were prepared through a hydrothermal process, followed by a calcination reaction in air. Oxygen incorporation in MoS2 expands the interlayer spacing and increases the defect degree, resulting in the decreased Na+ diffusion resistance. Benefiting from the integrated carbon fibers, the electronic conductivity of electrode can be improved. Vertical MoS2 nanosheets facilitate the permeation of electrolyte and shorten Na+ diffusion distance. The designed electrode displays high specific capacity, good rate capability and long-term stability due to the synergistic effect between oxygen incorporation in vertical MoS2 nanosheets and carbon fibers network. 2. Experimental 2.1 Preparation of OMSCF Commical wet tissue (Vinda Paper Group) was firstly soaked by 1 M HCl to eliminate the impurities, and then was washed by deionized water. Graphite oxide was synthesized through modified Hummers’ method. Graphene oxide (GO) suspension (1 mg mL-1) was prepared by dispersing graphite oxide in water.37 To enhance the mechanical strength of wet tissue after carbonization, GO (10 mL) suspension was coated on the wet tissue (10×15 cm2). The wet tissue (2×3 cm2) coated by GO was hydrothermal treatment with sodium molybdate (Na2MoO4, 0.24 g), thiourea (CH4N2, 0.76 g) to produce the MoS2/carbon fibers precursor. The MoS2/carbon fibers precursor was further calcined at the temperature of 800 oC, and kept at the temperature for 4 h in N2 atmosphere to obtain the MoS2/carbon fibers (MSCF). In order to incorporate the oxygen atoms in MoS2, the MoS2/carbon fibers were further calcined at 300, 400 and 500 oC (the furnace was in advance heated to the given temperature) for 15 min in air to obtain the corresponding to OMSCF300, OMSCF-400 and OMSCF-500, respectively. In comparison, the wet tissue-GO without MoS2 3



was directly calcined at the temperature of 800 oC, and kept at temperature for 4 h under N2 atmosphere to obtain the carbon fibers-reduced graphene oxide (carbon fibers/rGO) composite. 2.2 Structural characterization The morphologies of the samples were observed by field emission scanning electron microscopy (FESEM, JSM-6330F) and transmission electron microscopy (TEM, FEI Talos F200s) with an energy dispersive spectrometer (EDS). The structures were characterized by X-ray diffraction (XRD, Rigaku D/max X-ray diffractometer, Cu Ka radiation). Raman spectroscopy were measured by Jobin-Yvon Labor Raman HR-800. X-ray photoelectron spectroscopy (XPS) were carried out on AXIS-ULTRA DLD-600W system. Thermogravimetric analysis (TGA) was performed using a NETZSCH STA449F5 from 50 to 700 oC in O2. The Brunauer-Emmett-Teller (BET) was recorded using a ASAP 2460 instrument by N2 physisorption at 77 K. Fourier transform infrared spectroscopy (FTIR) was collected by Nicolet-MEXUS 670 Spectrophotometer. 2.3 Electrochemical characterization The electrodes were prepared by a simple procedure. Slurry of 10 wt% acetylene black, 10 wt% polyvinylidene difluoride and 80 wt% active materials (MSCF, OMSCF-300, OMSCF-400, OMSCF-500 and carbon fibers/rGO) was coated on Cu foil and dried in an oven at 120 oC for 12 h to obtain uniform film. The mass per unite area is about 1.5 mg cm-2. The electrolyte was consisted of 1 M NaPF6 in ethylene carbonate (EC) and dimethyl carbonate (DMC) (1:1 by volume). The counter electrode was sodium foil. The separator was Celgard 2400 membrane. The CR 2025 cointype cells were further assembled in a glovebox of Ar gas. Galvanostatically discharged/charged tests were performed at different current densities versus Na/Na+ from 0.01 to 3 V on a land CT2100. The cyclic voltammograms (CV) were collected on a CHI760C electrochemical workstation (Shanghai Chenhua) at different scan rates (0.05-1 mV s-1) with a voltage window of 0 4


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and 3 V. Electrochemical impedance spectra (EIS) were tested at the frequency range of 0.01 Hz and 100 kHz on a CHI760C electrochemical workstation. Moreover, full cells were assembled with OMSCF-400 as anode and Na3V2(PO4)2F3 as cathode. The weight ratio of OMSCF-400 anode to Na3V2(PO4)2F3 cathode was 1:4.2 in full cell. The galvanostatical charge/discharge tests were performed at 0.05 A g-1 between 1.2 and 3.8 V. 3. Results and discussion The schematic illustration of the fabrication process of OMSCF can be seen in Fig. 1a. The treated wet tissue coated by GO was firstly hydrothermal treatment with sodium molybdate and thiourea to get the MoS2/carbon fibers precursor. The MoS2/carbon fibers precursor was then calcined at 800 o

C in N2 to produce MSCF. Finally, MSCF was further calcined in air to obtain the OMSCF. The

morphology and incorporated oxygen contents in MoS2 were significantly influenced by the calcined temperature in air. Therefore, the different calcined temperatures (300, 400 and 500 oC) were employed to compare the morphology, structure and electrochemical performance of OMSCF300, OMSCF-400 and OMSCF-500 electrodes. The morphologies and structures of the samples were further characterized by SEM, TEM, HRTEM and EDS mapping. SEM images of MSCF are shown in Fig. 1b, 1c and 1d. The carbon fibers with a diameter of about 10 µm are uniformly coated with particles (Fig. 1b and 1c). The surface of the carbon fibers was covered with the spherical nanoflowers of ~500 nm in diameter. (Fig. 1d). The high magnification SEM image (Fig. 1d inset) indicates the vertical nanosheets of MoS2. After calcination of MSCF in air at 300 oC, the spherical nanoflowers are retained (Fig. S1a and S1b). OMSCF-400 exhibits the uniform encapsulation of MoS2 on the carbon fibers and typical carbon fibers core and MoS2 shell structure (Fig. 1e, Fig. 1f and Fig. 1f inset). High magnification SEM images show vertical MoS2 nanosheets wrapped around each carbon fiber (Fig. 1g and Fig. 1g inset). The morphology changes from nanoflowers to coated nanosheets after calcination at 400 oC may be attributed to the exothermic reaction. The exothermic reaction during the oxidation process of MoS2 leads to localized heat sufficient enough to sublime the MoS2 molecules, which changes 5



the morphology. The vertical nanosheets on the carbon fiber make for the penetration of electrolyte in electrode and shorten Na+ diffusion distance.38 In addition, the bulk and irregular sheets are found in the OMSCF-500 (Fig. S1c and S1d), indicating that the vertical nanosheets are destroyed at high calcination temperature. The irregular morphology of OMSCF-500 can be attributed to the broken carbon fibers and strong exothermic reaction during the oxidation process at 500 oC. Therefore, the proper annealing temperature is very important to obtain the uniform morphology. TEM image of OMSCF-400 further confirms the vertical and sheet structure (Fig. 1h). The selected area electron diffraction (SAED) pattern indicates the polycrystalline characteristics of MoS2 (Fig. 1h inset). HRTEM image indicates the interlayer spacing is expanded to 0.68 nm for OMSCF-400 (Fig. 1i). The expanded interlayer spacing is beneficial to increase the available contact area between MoS2 and electrolyte and decrease Na+ diffusion resistance. It is worth noting that the crystal fringes along the curled edge are discontinuous, which can be attributed to the existence of abundant defects cracking of the basal planes of OMSCF-400 (Fig. 1i).35 EDS elemental mapping definitely indicate the co-existence of Mo, S, O and C elements in OMSCF-400 (Fig. 1j), indicating the successful incorporation of O in OMSCF-400. XRD patterns shown in Fig. 2a indicate that MSCF and OMSCF-300 exhibit the similar diffraction peaks at about 14.2, 32.9, 39.5, and 58.7o, which are consistent with the (002), (100), (103) and (110) planes of MoS2 (No. 75-1539), suggesting that the structure of MoS2 was not changed after calcining at 300 oC in air. In the case of OMSCF-400, a left shift of 13.1o is displayed, indicating the expanded interlayer spacing of 2H-MoS2 after calcining at 400 oC in air. The peak at about 13.1o is corresponding to the d (002)-spacing of 0.68 nm and this phenomenon is in agreement with HRTEM image. The peaks at high-angle region (32.9o, 39.5o and 58.7o) do not shift, which can be attributed the same atomic arrangement along the basal planes.39 When the calcining temperature was increased to 500 oC, partial MoS2 is oxidized to MoO2 and MoO3. Raman spectra of MSCF and OMSCF-300 exhibit two main peaks appeared at ~ 1343 and ~1584 cm-1, which correspond to the disordered (D) and graphite (G) bands of carbon, respectively (Fig. 2b). Moreover, 6


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additional two peaks are also detected at 376 and 404 cm-1, which can be related to the E12g and A1g of MoS2 (Fig. 2b).40, 41 The existence of B1g and B2g of Mo-O bond at about 337 and 280 cm-1 are confirmed in the Raman spectrum of OMSCF-400 (Fig. 2b), indicating the successful oxygen incorporation in MoS2.42 OMSCF-500 displays obvious peaks at 376 and 404 cm-1, which are assigned to the MoS2. The peaks at about 280, 337, 819 and 992 cm-1 for OMSCF-500 are related to the MoO2 and MoO3.43, 44 XPS was further employed to analyze the elemental compositions and valence states of the samples. All of samples exhibit the presence of Mo, S, C and O elements (Fig. S2a). For the MSCF and OMSCF-400, the Mo3d spectra are dominated with Mo3d5/2 and Mo3d3/2 of Mo4+ at 229.4 and 232.6 eV, respectively, which are characteristic of MoS2 (Fig. 2c).45 At the same time a weak peak at 235.9 eV for OMSCF-400 is associated with Mo3d3/2 of Mo6+ because of the introduction of oxygen (Fig. 2c).46 In addition, a peak at 226.6 eV in the Mo3d region is S2s of MoS2 (Fig. 2c), which is in agreement with Mo-S bond. The S2p peaks at 162.2 and 163.4 eV are consistent with Mo-S and C-S, suggesting a small part of sulfur atoms incorporate into carbon (Fig. 2e).47 Compared with MSCF, the O1s spectrum of OMSCF-400 after fitting reveals an additional peak at about 530.1 eV, which can be ascribed to the Mo-O bond as shown in Fig. 2d.48 Moreover, OMSCF-500 exhibits the enhanced peaks at 232.6 and 235.9 eV in the Mo3d and 530.1 eV in the O1s spectra, which are the typical for the Mo3d3/2 of Mo4+ and Mo6+ in the MoO2 and MoO3 and Mo-O bond, respectively (Fig. S2b and S2c).46 FTIR of OMSCF-400 confirms the presence of S=O bond, which is not found in MSCF (Fig. S3).49 These results indicate the successful incorporation of oxygen in MoS2. TGA was performed in O2 from 50 to 700 oC to analyze the weight contents of MoS2 in OMSCF (Fig. 2f). The impurities in the carbon fibers/rGO are estimated to 6% according to the residual weight of carbon fibers/rGO after calcination. The oxidization of MoS2 to MoO2 and MoO3 and carbon to CO2 were occurred at 350-450 and 450-550 oC, respectively. According to the weight contents of MoO3 at 700 oC and impurities in the carbon fibers/rGO, the MoS2 in the MSCF, 7



OMSCF-300 and OMSCF-400 is estimated to 88 wt%, 83 wt% and 92 wt%. Moreover, OMSCF500 exhibits the increased weight from 350 to 450 oC, suggesting the oxidization of MoO2 to MoO3 in air.50 The total mass contents of MoS2, MoO2 and MoO3 in OMSCF-500 are about 96 wt%. The specific surface area, pore distribution and pore size of MSCF, OMSCF-300, OMSCF-400 and OMSCF-500 were analyzed by N2 adsorption and desorption isotherms. All of samples display typical IV isotherms, indicating that the samples are micropores and mesopores materials. The specific surface areas of MSCF, OMSCF-300 and OMSCF-400 are 33.8, 32.9 and 32.7 m2 g-1, respectively (Fig. 3a). The average pore diameters of MSCF, OMSCF-300 and OMSCF-400 are 18.9, 18.2, and 19.1 nm, respectively (Fig. 3b). These results indicate that the porous structure, pore size and specific surface area of MSCF are retained after annealing at 300 and 400 oC under air. However, OMSCF-500 exhibits a higher surface area of 153.2 m2 g-1 and lower average pore diameter of 15.8 nm than those electrodes, which can attributed to the broken and porous structure under high heating temperature. To investigate their suitability for Na+ storage, the electrochemical properties of OMSCF-400 electrode were measured by cyclic voltammetry (CV) and galvanostatic discharge/charge tests. CV curves of OMSCF-400 for the first three cycles in the range of 0-3.0 V (vs. Na/Na+) at a scanning rate of 0.05 mV s-1 were shown in Fig. 4a. During the initial discharge (sodium ions insertion) process, the peak at 2.1 V may be in agreement with the reduction of incorporated oxygen atoms and oxygen-containing groups in MoS2.46 This peak is also observed in the reported MoS2amorohous carbon electrode.46 Moreover, this peak is corresponding to the discharge plateau of OMSCF-400 at about 2.0 V, which is also observed in OMSCF-500 electrode (Fig. 4b and Fig. S4c). Another reduction peak located at 0.7 V originates from the formation of NaxMoS2 and solid electrolyte interface (SEI) layer due to Na+ insertion into in MoS2.51, 52 The peak at about 0.05 V can be identified, which are referenced to the insertion of Na+ in the carbon fibers and the decomposition of NaxMoS2 to Mo and NaxS.8,

53

In the following charge process (sodium ion

extraction), the peak at 1.81 V is in agreement with desodiation and the conversion of NaS2 to S.54, 8


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55

The nearly overlapping CV curves during the 2nd and 3rd indicate high reversibility of OMSCF-

400 electrode. The CV curves of MSCF exhibit the similar patterns with that of OMSCF-400 (Fig. S4). The absent peak at ~ 2.1 V in MSCF may be attributed to absence of incorporated oxygen atoms and oxygen-containing groups. This result indicates that the oxygen incorporation in MoS2 does not influence the electrochemical behaviour. The voltage-capacity curves of OMSCF-400 at 0.1 A g-1 are displayed in Fig. 4b. The first discharge and charge capacities of OMSCF-400 can reach 673 and 362 mAh g-1 (the specific capacity is calculated based on the total weight of MoS2, rGO and carbon fibers), with the 1st cycle coulombic efficiency of 54 %. The large initial irreversible capacity can be owing to the formation of SEI.56 In comparison, the discharge and charge capacities of MSCF, OMSCF-300 and OMSCF500 are 434 and 233 mAh g-1, 369 and 247 mAh g-1, 344 and 108 mAh g-1 at the first cycle, respectively (Fig. S5). Moreover, the reversible capacity of OMSCF-400 is as high as 330 mAh g-1 at 0.1 A g-1 after 100 cycles (Fig. 4c), corresponding to a high capacity retention of 91.2 %. However, after 100 cycles, MSCF and OMSCF-300 electrodes exhibit relatively high reversible capacities of 232 and 221 mAh g-1, compared with 60 mAh g-1 for OMSCF-500. The low reversible capacity of OMSCF-500 may be owing to the presence of MoO3 and MoO2 and the absence of carbon. The small lattice spacings of MoO3 and MoO2 increase the diffusion resistance for Na+ storage and reduce the capacity. The absence of carbon fibers in OMSCF-500 decreases the electronic conductivity and electron transfer. The rate capabilities of MSCF, OMSCF-300, OMSCF-400 and OMSCF-500 are compared in Fig. 4d. OMSCF-400 shows outstanding reversible capacities of 288, 268, 241 and 225 mAh g-1 at various current densities of 0.2, 0.3, 0.5 and 1 A g-1, respectively, which are much higher than those for MSCF, OMSCF-300 and OMSCF-500. As the current density reverses from 1 A g-1 to 0.2 A g-1, the specific capacity of OMSCF-400 regains 302 mAh g-1, which is much higher than 251 mAh g-1 for MSCF, 235 mAh g-1 for OMSCF-300 and 64 mAh g-1 for OMSCF-500. The slightly improved capacity of OMSCF-400 after cycles can be attributed to the exfoliated MoS2 layers, which produce 9



more defect sites and active reaction sites for Na+ storage.53 In addition, the increased capacity during cycles at large current density is also observed in other papers, which is attributed the interfacial storage and electrochemical reconstruction caused by structure and morphology variation of electrodes after cycles.57-59 The small MoS2 nanosheets may have highly active due to the increased surface area. The cycling stability of OMSCF-400 at 1 A g-1 was further confirmed in Fig. 4e. The reversible capacity of OMSCF-400 is about 181 mAh g-1 after 100 cycles, which is more than twice as those of MSCF (87 mAh g-1) and OMSCF-300 (79 mAh g-1) and eight times as high as that of OMSCF-500 (21 mAh g-1). To confirm the high capacity contributed by the MoS2 in the OMSCF-400 electrode, the carbon fibers/rGO electrode was tested. The carbon fibers/rGO electrode displays low charge capacities of 75 (at 0.1 A g-1, 50 cycles) and 60 mAh g-1 (1 A g-1, 280 cycles) (Fig. S6), which further confirms that the high reversible capacity of OMSCF-400 is contributed by oxygen incorporation in MoS2. Due to the unique structure, this electrode prepared in our work exhibits enhanced specific capacity compared with the reported MoS2-based electrodes (Table 1). 39, 53, 55, 56, 60-65 The excellent sodium-ion storage properties of OMSCF-400 can be attributed the synergistic effects of oxygen incorporation in MoS2 and vertical nanosheets as well as carbon fibers network. OMSCF-400 electrode with expanded interlayer distances caused by oxygen incorporation can facilitate the reversible Na+ intercalation/deintercalation and reduce the ion diffusion resistance. The vertical and open structure of MoS2 can further shorten the diffusion pathways for Na+ and increase the contact area of electrode and electrolyte. The carbon fibers with high electronic conductivity can ensure efficient electron transfer. The coated rGO on the carbon fibers can provide the intimate contact between MoS2 and carbon fibers matrix and facilitate the electron transportation. EIS spectra of MSCF, OMSCF-300, OMSCF-400 and OMSCF-500 electrodes before cycling are compared in Fig. 4f. All of the plots show a depressed semicircle and an inclined line. Ohmic resistance (Re, the intercepts with real impedance axis) is related to the electrical resistance from electrode and ionic resistance from separator. The semicircle corresponds to the charge transfer 10


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resistance Rct at the electrode/electrolyte interface. It is clearly that OMSCF-400 electrode presents the lowest charge-transfer resistance, indicating the enhanced electrochemical kinetics. According to the equivalent circuit (Fig. 4i inset A), the value of Rct for OMSCF-400 is about 4060 Ω, which is lower than those of MSCF, OMSCF-300 and OMSCF-500 (Table 2). In addition, Na+ diffusion coefficient can be calculated from the relationship between Z’ and the reciprocal square root of the lower angular frequencies (ω-1/2) (Fig. 4g).66, 67 As listed in Table 2, OMSCF-400 electrode exhibits the highest Na+ diffusion coefficient of 1.8×10-12 cm2 s-1, indicating the improved Na+ diffusion mobility and decreased Na+ diffusion resistance by oxygen incorporation in MoS2. These results further explain the excellent electrochemical performance of OMSCF-400 electrode. Moreover, EIS of OMSCF-400 electrodes after cycling are compared in Fig. 4h. After cycling, the semicircle is related to the overlap between the SEI (Rf) and charge-transfer resistance (Rct).68-70 Compared with the value of Rct before cycling, Rct obviously decreases after 5 cycles. With the increased cycles, the charge transfer resistance continues decreasing and stabilizes at about 440 Ω at the tenth cycle according to the equivalent circuit (Fig. 4i inset B). The decreased Rct may be owing to the enhanced ionic and electronic transfer kinetics after the gradual permeation of the electrolyte in electrode along with cycling. This result further confirms that the reversible capacity stabilize after 10 cycles, which is in agreement with the cycling performance in Fig. 4d. To better understand the discharge-charge mechanism of OMSCF-400 electrode for SIBs, CV measurements at the increased scanning rates between 0.2 and 1.0 mV s-1 were exhibited (Fig. 5a). The area of closed CV curves exhibits the total charge storage included of faradaic and non-faradaic process. The degree of capacitive effect can be qualitatively calculated in the light of the following equation between responsive current i (mA) and scanning rate v (mV s-1) from the CV curves: i = avb

(1)

where a and b are both variable parameters. The b value is between 0.5 and 1.0, determining by the slope of the log i versus log v in equation (1). The slope b of 0.5 implies a diffusion-controlled 11



mechanism (battery behavior), whereas that of 1.0 means a surface capacitive response (capacitor behavior).71, 72The slopes of the reduction peak (1.28 V) and the oxidation peak (2.15 V) are 0.71 and 0.80, indicating a mixed contribution from both behaviors (Fig. 5b). In addition, the contribution from surface-controlled capacitive (k1v) and diffusion-controlled battery reaction (k2v1/2) can be quantitatively analyzed based on the following equations: i(V)=k1v+k2v1/2

(2)

i(V)/v1/2= k1v1/2+ k2

(3)

The k1 and k2 can be obtained through the plotting the v1/2 vs. i/v1/2. According the equations (2) and (3), the capacitive contribution from two different charge storage processes can be determined. 73% of the total charge from capacitive process at 1.0 mV s-1 can be observed (Fig. 5c). The proportion of capacitive contribution gradually improves from 54.8 % to 73.0 % when the scan rate increases from 0.2 to 1.0 mV s-1 (Fig. 5d). The high capacitive contribution may be from the relatively high specific surface area caused by vertical MoS2 nanosheets array. The high capacitive contribution can improve the rate capability and cycling life.8, 73, 74 To confirm the potential applicability, full cells with OMSCF-400 anodes and Na3V2(PO4)2F3 cathodes (the preparation process and electrochemical performance were exhibited in Supporting Information and Fig. S7) were further investigated. The charge-discharge curves of full cell during the first three cycles at 0.05 A g-1 (based on the total weight of OMSCF-400 anode) are exhibited in Fig. 6a. The charge and discharge capacities are 424 and 243, 288 and 223, 265 and 221 mAh g-1 during the first three cycles, respectively. After 20 cycles, the reversible capacity is about 209 mAh g-1 for full cell, indicating good cycling performance (Fig. 6b). To reveal the structure and morphology changes of OMSCF-400 after cycles, XRD, SEM and TEM were performed (~3 V vs. Na/Na+, 60th cycles). After cycles, the peaks located at 21.0, 23.0, 25.8 and 29.2o can be attributed to S. The peak at about 38.9o references to Mo. The peaks at about 33.3 and 56.1o are corresponding to MoS2. This result indicates the conversion of Na2S to S during 12


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the charge process. The electrode is mixture of S, Mo and some MoS2 after cycles, which is in agreement with reported paper (Fig. 7a).75 SEM image indicates the expanded nanoflowers after cycles (Fig. 7b). TEM and HRTEM images confirm the uniform dispersion of S, Mo and MoS2 on the carbon sheets (Fig, 7c and 7d). EDS mapping images after cycles further confirm the uniform distribution of Mo, S, O and C elements of OMSCF-400 electrode (Fig. S8). 4. Conclusions In summary, the integrated vertical oxygen incorporation in MoS2 nanosheets with carbon fibers electrode has been prepared though hydrothermal reaction together with annealing in air. Oxygen incorporation in MoS2 expands the interlayer spacing and improves the degree of defect, resulting in the decreased ion diffusion resistance and increased capacity. The vertical nanosheets make for the permeation of electrolyte and increase active contact area. The integrated carbon fibers further enhance the electronical conductivity of the entire electrode. These features greatly enhance the capacity, rate and cycling performance as anode for SIBs. The electrode displays high capacity of 330 mAh g-1 after 100 cycles at 0.1 A g-1 along with excellent rate capability. This work shows a simple and effective method for designing and preparing the high-performance electrode applied in SIBs. Acknowledgments The authors acknowledge the financial support by the National Key R&D Program of China (2018YFB0905400), NSFC (51772169, 51402168, 51672158) and the Outstanding Youth Science and Technology Innovation Team Project of Hubei Educational Committee (T201603). Appendix A. Supporting information 13



Supplementary data (the preparation process and electrochemical tests of Na3V2(PO4)2F3; FESEM images of OMSCF-300 and OMSCF-500; XPS spectra of MSCF, OMSCF-300, OMSCF-400 and OMSCF-500; XPS spectra of Mo3d and O1s for OMSCF-500; FTIR of MSCF, OMSCF-400 and OMSCF-500; CV curves of MSCF; Discharge/charge profiles of MSCF, OMSCF-300 and OMSCF-500; Discharge/charge profiles and cycling performance of carbon fibers/rGO and Na3V2(PO4)2F3; EDS mapping images of S, Mo, O and C elements of OMSCF-400 after cycles) is available free of charge on the ACS Publications website at DOI: ). References (1) Armand, M.; Tarascon, J.M. Issues and Challenges Facing Rechargeable Lithium Batteries. Nature 2008, 414, 359-367. (2) Goodenough, J.B.; Park, K.S. The Li-ion Rechargeable Battery: A Perspective. J. Am. Chem. Soc. 2013, 135, 1167-1176. (3) Ellis, B.L.; Nazar, L.F. Sodium and Sodium-Ion Energy Storage Batteries. Curr. Opin. Solid State Mater. Sci. 2012, 16, 168-177. (4) Ong, S.P.; Chevrier, V.L.; Hautier, G.; Jain, A.; Moore, C.; Kim, S.; Ma, X.H.; Ceder, G. Voltage, Stability and Diffusion Barrier Differences between Sodium-Ion and Lithium-Ion Intercalation Materials. Energy Environ. Sci. 2011, 4, 3680-3688.

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Page 14 of 38

Page 15 of 38 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(5) Guo, S.H.; Liu, P.; Yu, H.J.; Zhu, Y.B.; Chen, M.W.; Ishida, M.; Zhou, H.S. A Layered P2and O3-Type Composite as a High-Energy Cathode for Rechargeable Sodium-Ion Batteries. Angew. Chem. Int. Ed. 2015, 54, 5894-5899. (6) Zhang, B.; Ghimbeu, C.M.; Laberty, C.; Vix-Guterl, C.; Tarascon, J.M. Correlation between Microstructure and Na Storage Behavior in Hard Carbon. Adv. Energy Mater. 2016, 6, 1501588. (7) Liu, Y.H.; Yu, X.Y.; Fang, Y.J.; Zhu,X.S.; Bao, J.C.; Zhou, X.S.; Wen, X.; Lou, (David) Confining SnS2 Ultrathin Nanosheets in Hollow Carbon Nanostructures for Efficient Capacitive Sodium Storage. Joule 2018, 2, 725-735. (8) Zhang, S.; Yu, X.B.; Yu, H.L.; Chen, Y.J.; Gao, P.; Li, C.Y.; Zhu, C.L. Growth of Ultrathin MoS2 Nanosheets with Expanded Spacing of (002) Plane on Carbon Nanotubes for HighPerformance Sodium-Ion Battery Anodes. ACS Appl. Mater. Interfaces 2014, 6, 21880-21885. (9) Li, G.; Luo, D.; Wang, X.L.; Seo, M.H.; Hemmati, S.; Yu, A.; Chen, Z.W. Enhanced Reversible Sodium-Ion Intercalation by Synergistic Coupling of Few-Layered MoS2 and Sdoped Graphene. Adv. Funct. Mater. 2017, 27, 1702562. (10) Zhou, X.S.; Wan, L.J.; Guo, Y.G. Facile Synthesis of MoS2@CMK-3 Nanocomposite as an Improved Anode Material for Lithium-Ion Batteries. Nanoscale 2012, 4, 5868-5871. (11) Zhou, X.S.; Wan, L.J.; Guo, Y.G. Synthesis of MoS2 Nanosheet-Graphene Nanosheet Hybrid Materials for Stable Lithium Storage. Chem. Commun 2013, 49, 1838-1840.

15



(12) Wang, J.; Liu, J.; Yang, H.; Chao, D.; Yan, J.; Savilov, S.V.; Lin, J.; Shen, Z.X. MoS2 Nanosheets Decorated Ni3S2@MoS2 Coaxial Nanofibers: Constructing an Ideal Heterostructure for Enhanced Na-Ion Storage. Nano Energy 2016, 20, 1-10. (13) Matte, H.S.S.R.; Gomathi, A.; Manna, A.K.; Late, D.J.; Datta, R.; Pati, S.K.; Rao, C.N.R. MoS2 and WS2 Analogues of Graphene. Angew. Chem. Int. Ed. 2010, 122, 6033-6041. (14) Stephenson, T.; Li, Z.; Olsen, B.; Mitlin, D. Lithium Ion Battery Applications of Molybdenum Disulfide (MoS2) Nanocomposites. Energy Environ. Sci. 2014, 7, 209-231. (15) Ren, W.N.; Zhou, W.W.; Zhang, H.F.; Cheng, C.W. ALD TiO2-Coated Flower-like MoS2 Nanosheets on Carbon Cloth as Sodium Ion Battery Anode with Enhanced Cycling Stability and Rate Capability. ACS Appl. Mater. Interfaces 2017, 9, 487-495. (16) Zhu, X.Q.; Liang, X.Y.; Fan, X.B.; Su, X.T. Fabrication of Flower-Like MoS2/TiO2 Hybrid as an Anode Material for Lithium Ion Batteries. RSC Adv. 2017, 7, 38119-38124. (17) Jeong, Y.C.; Kim, J.H.; Kwon, S.H.; Oh, J.Y.; Park, J.; Jung, Y.; Lee, S.G.; Yang, S.J.; Park, C.R. Rational Design of Exfoliated 1T MoS2@CNT-Based Bifunctional Separators for Lithium Sulfur Batteries. J. Mater. Chem. A 2017, 5, 23909-23918. (18) Li, M.C.; Wu, Z.; Wang, Z.Y.; Yu, S.C.; Zhu, Y.G.; Nan, B.; Shi, Y.; Gu, Y.Y.; Liu, H.T.; Tang, Y.G.; Lu, Z.G. Facile Synthesis of Ultrathin MoS2/C Nanosheets for use in Sodium-Ion Batteries. RSC Adv. 2017, 7, 285-289.

16


Page 16 of 38

Page 17 of 38 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(19) Wang, Y.; Qu, Q.T.; Li, G.C.; Gao, T.; Qian, F.; Shao, J.; Liu, W.J.; Shi, Q.; Zheng, H.H. 3D Interconnected and Multiwalled Carbon@MoS2@Carbon Hollow Nanocables as Outstanding Anodes for Na-Ion Batteries. Small 2016, 12, 5915-5919. (20) Wang, P.P.; Sun, H.; Ji, Y.; Li, W.; Wang, X. Three-Dimensional Assembly of Single-Layered MoS2. Adv. Mater. 2014, 26, 964-969. (21) Xie, X.Q.; Ao, Z.M.; Su, D.W.; Zhang, J.Q.; Wang, G.X. MoS2/Graphene Composite Anodes with Enhanced Performance for Sodium-Ion Batteries: The Role of the Two-Dimensional Heterointerface. Adv. Funct. Mater. 2015, 25, 1393-1403. (22) Ding, S.; Chen, J.S.; Lou, X.W. Glucose-Assisted Growth of MoS2 Nanosheets on CNT Backbone for Improved Lithium Storage Properties. Chem. Eur. J. 2011, 17, 13142-13145. (23) Choi, S.H.; Kang, Y.C. Synergetic Effect of Yolk-Shell Structure and Uniform Mixing of SnSMoS2 Nanocrystals for Improved Na-Ion Storage Capabilities. ACS Appl. Mater. Interfaces 2015, 7, 24694-24702. (24) Wang, Y.X.; Chou, S.L.; Wexler, D.; Liu, H.K.; Dou, S.X. High-Performance Sodium-Ion Batteries and Sodium-Ion Pseudocapacitors Based on MoS2/graphene Composites. Chem. 2014, 20, 9607-9612. (25) Wang, H.Y.; Jiang, H.; Hu, Y.J.; Li, N.; Zhao, X.J.; Li, C.Z. 2D MoS2/polyaniline Heterostructures with Enlarged Interlayer Spacing for Superior Lithium and Sodium Storage. J. Mater. Chem. A 2017, 5, 5383-5389.

17



(26) Wang, Y.S.; Ma, Z.M.; Chen, Y.J.; Zou, M.C.; Yousaf, M.; Yang, Y.B.; Yang, L.S.; Cao, A.Y.; Han, R.P.S. Controlled Synthesis of Core-Shell Carbon@MoS2 Nanotube Sponges as HighPerformance Battery Electrodes. Adv. Mater. 2016, 28, 10175-10181. (27) Shan, X.Y.; Zhang, S.; Zhang, N.; Chen, Y.J.; Gao, H.; Zhang, X.T. Synthesis and Characterization of Three-Dimensional MoS2@Carbon Fibers Hierarchical Architecture with High Capacity and High Mass Loading for Li-Ion Batteries. J. Colloid Interface Sci. 2018, 510, 327-333. (28) Wang, C.; Wan, W.; Huang, Y.H.; Chen, J.T.; Zhou, H.H.; Zhang, X.X. Hierarchical MoS2 Nanosheet/active Carbon Fiber Cloth as a Binder-free and Free-standing Anode for LithiumIon Batteries. Nanoscale 2014, 6, 5351-5358. (29) Chen, B.B.; Li, X.F.; Li, X.; Yang, J.; Peng, W.X.; Dong, J.Z.; Li, C.S.; Song, H.J. Facile Fabrication of Hierarchical Carbon Fiber-MoS2 Ultrathin Nanosheets and its Tribological Properties. RSC Adv. 2016, 6, 60446-60453. (30) Miao, Y.E.; Huang, Y.P.; Zhang, L.S.; Fan, W.; Lai, F.L.; Liu, T.X. Electrospun Porous Carbon Nanofiber@MoS2 Core/Sheath Fiber Membranes as Highly Flexible and Binder-free Anodes for Lithium-Ion Batteries. Nanoscale 2015, 7, 11093-11101. (31) Tang, Y.J.; Wang, Y.; Wang, X.L.; Li, S.L.; Huang, W.; Dong, L.Z.; Liu, C.H.; Li, Y.F.; Lan, Y.Q. Molybdenum Disulfide/Nitrogen-Doped Reduced Graphene Oxide Nanocomposite with

18


Page 18 of 38

Page 19 of 38 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Enlarged Interlayer Spacing for Electrocatalytic Hydrogen Evolution. Adv. Energy Mater. 2016, 6, 1600116. (32) Sun, Y.G.; Alimohammadi, F.; Zhang, D.T.; Guo, G.S. Enabling Colloidal Synthesis of EdgeOriented MoS2 with Expanded Interlayer Spacing for Enhanced HER Catalysis. Nano Lett. 2017, 17, 1963-1969. (33) Xiang, T.; Fang, Q.; Xie, H.; Wu, C.; Wang, C.; Zhou, Y.; Liu, D.; Chen, S.; Khalil, A.; Tao, S.; Liu, Q.; Song, L. Vertical 1T-MoS2 Nanosheets with Expanded Interlayer Spacing Edged on a Graphene Frame for High rate Lithium-Ion Batteries. Nanoscale 2017, 9, 6975-6983. (34) Liu, P.T.; Zhu, J.Y.; Zhang, J.Y.; Xi, P.X.; Tao, K.; Gao, D.Q.; Xue, D.S. P Dopants Triggered new Basal Plane Active Sites and Enlarged Interlayer Spacing in MoS2 Nanosheets toward Electrocatalytic Hydrogen Evolution. ACS Energy Lett. 2017, 2, 745-752. (35) Zhang, L.S.; Fan, W.; Liu, T.X. Flexible Free-standing Defect-rich MoS2/Graphene/Carbon Nanotube Hybrid Paper as Binder-free Anode for High-Performance Lithium Ion Batteries. RSC Adv. 2015, 5, 43130-43140. (36) Zhang, L.S.; Fan, W.; Liu, T.X. 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.

19



(37) Zhu, X.J.; Zhu, Y.W.; Murali, S.; Stoller, M.D.; Ruoff, R.S. Nanostructured Reduced Graphene Oxide/Fe2O3 Composite as a High-Performance Anode Material for Lithium Ion Batteries. ACS Nano 2011, 5, 3333-3338. (38) Yang, F.; Wan, Q.; Duan, X.C.; Guo, W.; Mao, Y.H.; Ma, J.M. N-doped Carbon/MoS2 Composites as an Excellent Battery Anode. RSC Adv. 2016, 6, 18583-18586. (39) Xie J.; Zhang, J.; Li, S.; Grote, F.; Zhang, X.; Zhang, H.; Wang, R.; Lei, Y.; Pan, B.; Xie, Y. Controllable Disorder Engineering in Oxygen-Incorporated MoS2 Ultrathin Nanosheets for Efficient Hydrogen Evolution. J. Am. Chem. Soc. 2013, 136, 17881-17888. (40) David, L.; Bhandavat, R.; Singh, G. MoS2/Graphene Composite Paper for Sodium-Ion Battery Electrodes. ACS Nano 2014, 8, 1759-1770. (41) Wang, X.W.; Zhang, Z.A.; Chen, Y.Q.; Qu, Y.H.; Lai, Y.Q.; Li, J. Morphology-Controlled Synthesis of MoS2 Nanostructures with Different Lithium Storage Properties. J. Alloys. Compd. 2014, 600, 84-90. (42) Deng, Z.N.; Hu, Y.J.; Ren, D.Y.; Lin, S.L.; Jiang, H.; Li, C.Z. Reciprocal Hybridization of MoO2 Nanoparticles and Few-Layer MoS2 for Stable Lithium-Ion Batteries. Chem. Commun. 2015, 51, 13838-13841. (43) Sun, Y.M.; Hu, X.L.; Luo, W.; Huang, Y.H. Self-Assembled Hierarchical MoO2/Graphene Nanoarchitectures and Their Application as a High-performance Anode Material for LithiumIon Batteries. ACS Nano 2011, 5, 7100-7107.

20


Page 20 of 38

Page 21 of 38 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(44) Yang, X.; Chen, W.; Liu, Y.L.; Li, Y.; Qi, Y.Y. Preparation of MoO2 Nanoparticles/rGO Nanocomposites and Their High Electrochemical Properties for Lithium Ion Batteries. J. Mater. Sci: Mater. Electron. 2017, 28, 1740-1749. (45) Zhou, W.J.; Zhou, K.; Hou, D.M.; Liu, X.J.; Li, G.Q.; Sang, Y.H.; Liu, H.; Li, L.G.; Chen, S.W. Three-Dimensional Hierarchical Frameworks Based on MoS2 Nanosheets SelfAssembled on Graphene Oxide for Efficient Electrocatalytic Hydrogen Evolution. ACS Appl. Mater. Interfaces 2014, 6, 21534-21540. (46) Chang, K.; Chen, W.X.; Ma, L.; Li, H.; Li, H.; Huang, F.H.; Xu, Z.D.; Zhang, Q.B.; Lee, J.Y. Graphene-Like MoS2/Amorphous Carbon Composites with High Capacity and Excellent Stability as Anode Materials for Lithium Ion Batteries. J. Mater. Chem. 2011, 21, 6251-6257. (47) Liu, H.D.; Hu, H.T.; Wang, J.; Niehoff, P.; He, X.; Paillard, E.; Eder, D.; Winter, M.; Li, J. Hierarchical Ternary MoO2/MoS2/Heteroatom-Doped Carbon Hybrid Materials for HighPerformance Lithium-Ion Storage. ChemElectroChem 2016, 3, 922-932. (48) Zhao, C.T.; Yu, C.; Zhang, M.D.; Huang, H.W.; Li, S.F.; Han, X.T.; Liu, Z.B.; Yang, J.; Xiao, W.; Liang, J.N.; Sun, X.L.; Qiu, J.S. A Review on Design Strategies for Carbon Based Metal Oxides and Sulfides Nanocomposites for High Performance Li and Na Ion Battery Anodes. Adv. Energy Mater. 2017, 7, 1601424.

21



(49) Ashraf, H.; Zhou, Y.; Xu, J.; Ahmad, K.; Yu, Z.W. Microscopic Study of Binary Mixtures between Pyrrolidinium Bis(triflorosulfonyl)imide and Dimethyl Sulfoxide/Acetonitrile. Sci. China Chem. 2016, 59, 578-586. (50) Zhang, H.J.; Wu, T.H.; Wang, K.X.; Wu, X.Y.; Chen, X.T.; Jiang, Y.M.; Wei, X.; Chen, J.S. Uniform Hierarchical MoO2/Carbon Spheres with High Cycling Performance for Lithium Ion Batteries. J. Mater. Chem. A 2013, 1, 12038-12043. (51) Xiao, J.; Wang, X.J.; Yang, X.Q.; Xun, S.D.; Liu, G.; Koech, P.K.; Liu, J.; Lemmon, J.P. Electrochemically Induced High Capacity Displacement Reaction of PEO/MoS2/Graphene Nanocomposites with Lithium. Adv. Funct. Mater. 2011, 21, 2840-2846. (52) Hu, Z.; Liu, Q.N.; Sun, W.Y.; Li, W.J.; Tao, Z.L.; Chou, S.L.; Chen, J.; Dou, S.X. MoS2 with Intercalation Reaction as Long-life Anode Material for Lithium Ion Batteries. Inorg. Chem. Front. 2016, 3, 532-535. (53) Hu, Z.; Wang, L.X.; Zhang, K.; Wang, J.B.; Cheng, F.Y.; Tao, Z.L.; Chen, J. Nanoflowers with Expanded Interlayers as High-Performance Anodes for Sodium-Ion Batteries. Angew. Chem. Int. Ed. 2014, 53, 12794-12798. (54) Park, J.; Kim, J.S.; Park, J.W.; Nam, T.H.; Kim, K.W.; Ahn, J.H.; Wang, G.X.; Ahn, H.J. Discharge Mechanism of MoS2 for Sodium Ion Battery: Electrochemical Measurements and Characterization. Electrochim. Acta 2013, 92, 427-432.

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Page 22 of 38

Page 23 of 38 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(55) Geng, X.M.; Jiao, Y.C.; Han, Y.; Mukhopadhyay, A.; Yang, L.; Zhu, H.L. Batteries: Freestanding Metallic 1T MoS2 with Dual Ion Diffusion Paths as High Rate Anode for SodiumIon Batteries. Adv. Funct. Mater. 2017, 27, 1702998. (56) Poizot, P.; Laruelle, S.; Grugeon, S.; Dupont, L.; Tarascon, J.M. Searching for New Anode Materials for the Li-Ion Technology: Time to Deviate from the Usual Path. J. Power Sources 2001, 97, 235-239. (57) Ni, S.B.; Ma, J.J.; Zhang, J.C.; Yang, X.L.; Zhang, L.L. Excellent Electrochemical Performance of NiV3O8/Natural Graphite Anodes via Novel in Situ Electrochemical Reconstruction. Chem. Commun. 2015, 51, 5880-5882. (58) Sun, Y.M.; Hu, X.L.; Luo, W.; Xia, F.F.; Huang, Y.H. Reconstruction of Conformal Nanoscale MnO on Graphene as a High ‐ Capacity and Long ‐ Life Anode Material for Lithium Ion Batteries. Adv. Funct. Mater. 2013, 23, 2436-2444. (59) Ni, S.B.; Zhang, J.C.; Ma, J.J.; Yang, X.L.; Zhang, L.L.; Li, X.M.; Zeng, H.B. Approaching the Theoretical Capacity of Li3VO4 via Electrochemical Reconstruction. Adv. Mater. Interfaces 2016, 3, 1500340. (60) Wu, Y.T.; Nie, P.; Jiang, J.M.; Ding, B.; Dou, H.; Zhang, X.G. MoS2 Nanosheets Decorated 2D Titanium Carbide (MXene) as High-performance Anodes for Sodium-Ion Batteries. ChemElectroChem 2017, 4, 1560-1565.

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Page 24 of 38

(61) Bang, G.S.; Kwan, Nam W.; Kim, J.Y.; Shin, J.; Choi, J.W.; Choi, S.Y. Effective LiquidPhase Exfoliation and Sodium Ion Battery Application of MoS2 Nanosheets. ACS Appl. Mater. Interfaces 2014, 6, 7084-7089. (62) Zhu, H.L.; Zhang, F.; Li, J.R.; Tang, Y.B. Penne-Like MoS2/Carbon Nanocomposite as Anode for Sodium-Ion-Based Dual-Ion Battery. Small 2018, 1703951. (63) Qin, W.; Chen, T.; Pan, L.; Niu, L.; Hu, B.; Li, D.; Li, J.; Sun, Z. MoS2-reduced Graphene Oxide Composites via Microwave Assisted Synthesis for Sodium Ion Battery Anode with Improved Capacity and Cycling Performance. Electrochim. Acta 2015, 153, 55-61. (64) Li, Y.; Liang, Y.; Hernandez, F.C.R.; Yoo, H.D.; An, Q.; Yao, Y. Enhancing Sodium-Ion Battery Performance with Interlayer Expanded MoS2-PEO Nanocomposites. Nano Energy 2015, 15, 453-461. (65) Sahu, T. S.; Mitra, S. Exfoliated MoS2 Sheets and Reduced Graphene Oxide-An Excellent and Fast Anode for Sodium-Ion Battery. Sci. Rep. 2015, 5, 12571. (66) Li, M.; Zhang, L.L.; Yang, X.L.; Huang, Y.H.; Sun, H.B.; Ni, S.B.; Tao, H.C. Synthesis and Electrochemical Performance of Li2FeSiO4/C Cathode Material using Ascorbic Acid as an Additive. J Solid State Electrochem 2015, 19, 415-421. (67) Zhang, L.L.; Duan, S.; Yang, X.L.; Peng, G.; Liang, G.; Huang, Y.H.; Jiang, Y.; Ni, S.B.; Li, M.

Reduced

Graphene

Oxide

Modified

Li2FeSiO4/C

24


Composite

with

Enhanced

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Electrochemical Performance as Cathode Material for Lithium Ion Batteries. ACS Appl. Mater. Interfaces 2013, 5, 12304-12309. (68) Chang, K.; Geng, D.S.; Li, X.F.; Yang, J.L.; Tang, Y.J.; Cai, M.; Li, R.Y.; Sun, X.L. Ultrathin MoS2/Nitrogen-Doped Graphene Nanosheets with Highly Reversible Lithium Storage. Adv. Energy Mater. 2013, 3, 839-844. (69) Verma, P.; Maire, P.; Novák, P. A Review of the Features and Analyses of the Solid Electrolyte Interphase in Li-Ion Batteries. Electrochim. Acta 2010, 55, 6332-6341. (70) Shi, Z.T.; Kang, W.P.; Xu, J.; Sun, L.L.; Wu, C.Y.; Wang, L.; Yu, Y.Q.; Zhang, W.J.; Lee, C.S. In Situ Carbon-doped Mo(Se0.85S0.15)2 Hierarchical Nanotubes as Stable Anodes for HighPerformance Sodium-Ion Batteries. Small 2015, 11, 5667-5674. (71) Niu, F.; Yang, J.; Wang, N.N.; Zhang, D.P; Fan, W.L.; Yang, J.; Qian, Y.T. MoSe2-covered N,P-doped Carbon Nanosheets as a Long-life and High-rate Anode Material for Sodium-Ion Batteries. Adv. Funct. Mater. 2017, 27, 170052. (72) Chao, D.L.; Liang, P.; Chen, Z.; Bai, L.Y.; Shen, H.; Liu, X.X.; Xia, X.H.; Zhao, Y.L.; Savilov, S.V.; Lin, J.Y.; Shen, Z.X. Pseudocapacitive Na-Ion Storage Boosts High Rate and Areal Capacity of Self-branched 2D Layered Metal Chalcogenide Nanoarrays. ACS Nano 2016, 10, 10211-10219. (73) Simon, P.; Gogotsi, Y.; Dunn, B. Pseudocapacitive Contributions to Electrochemical Energy Storage in TiO2. J. Phys. Chem. C 2007, 111, 14925-14931.

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(74) Hu, Z.; Zhu, Z.; Cheng, F.; Zhang, K.; Wang, J.; Chen, C.; Chen, J. Pyrite FeS for High-rate and Long-Life Rechargeable Sodium Batteries. Energy Environ. Sci. 2015, 8, 1309-1316. (75) Wang, Y.Z.; Shan, X.Y.; Wang, D.W.; Sun, Z.H.; Cheng, H.M.; Li, F. A Rechargeable Quasisymmetrical MoS2 Battery. Joule 2018, 2, 1-9.

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Table 1 Comparison of Na+ storage performance of MoS2-based electrodes with reported papers. Material

Current density

Capacity

(mA g-1)

(mAh g-1)/cycle

MoS2-graphene

25

218/200

(39)

MoS2 nanoflowers

50

350/300

(53)

1T MoS2-graphene

50

313/200

(55)

MoS2-graphene

100

312/200

(56)

MoS2 nanosheets

100

251/100

(60)

MoS2 nanosheets

20

150/100

(61)

MoS2-carbon

0.3C (1C=670 mA g-1)

315/200

(62)

MoS2-reduced graphene oxide

100

305/50

(63)

0.05C (1C=670 mA g-1)

150/70

(64)

0.05C (1C=670 mA g-1)

203/100

(65)

100

330/100

this work

PEO-MoS2 nanocomposites MoS2 sheets and reduced graphene oxide MoS2 nanosheets/carbon fibers

27


Ref.


Page 28 of 38

Table 2. Charge transfer resistance (Rct) and sodium ion diffusion coefficient (DNa+) for the samples. Sample

MSCF

OMSCF-300

OMSCF-400

OMSCF-500

Rct (Ω)

6088

5156

4060

6309

DNa+ (cm2 s-1)

7.5×10-13

9.3×10-13

1.8×10-12

7.6×10-13

28


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Figure captions: Fig. 1. (a) Schematic illustration of the preparation process of OMSCF. FESEM images of (b, c and d) MSCF and (e, f and g) OMSCF-400. The inset in (d) is high-magnification FESEM image of MSCF. The insets in (f) and (g) are high-magnification FESEM images of OMSCF-400. (h) TEM and (i) HRTEM images of OMSCF-400. The inset in (h) is SAED pattern. The inset in (i) is the corresponding intensity profile for the line scan across the lattice fringes. (j) TEM image and the corresponding EDS mapping of O, Mo, S and C elements.

Fig. 2. (a) XRD patterns and (b) Raman spectra of MSCF, OMSCF-300, OMSCF-400 and OMSCF500. XPS spectra of (c) Mo3d, (d) O1s and (e) S2p for MSCF and OMSCF-400. (f) TGA curves of carbon fibers/rGO, MSCF, OMSCF-300, OMSCF-400 and OMSCF-500.

Fig. 3. (a) Nitrogen adsorption and desorption isotherms and (b) the pore-size distribution of MSCF, OMSCF-300, OMSCF-400 and OMSCF-500. The inset in (b) is detailed view.

Fig. 4. (a) CV curves of OMSCF-400 electrode at 0.05 mV s-1. (b) Galvanostatic discharge/charge profiles of OMSCF-400 for the first three cycles at 0.1 A g-1. Cycling performance of MSCF, OMSCF-300, OMSCF-400 and OMSCF-500 at (c) 0.1 A g-1 and (e) 1 A g-1. (d) Rate performance of MSCF, OMSCF-300, OMSCF-400 and OMSCF-500. (f) EIS curves and (g) the relationship between Z’ and ω-1/2 in the low-frequency range of MSCF, OMSCF-300, OMSCF-400 and OMSCF-500. (h) EIS of OMSCF-400 electrode after various cycles. All impedance measurements were made at the fully charged state. (i) Equivalent circuit used to describe the Na+ insertion/extraction process for the electrodes (A) before and (B) after cycling. 29



Fig. 5. (a) CV curves of OMSCF-400 at various scan rates. (b) Plots of log (scan rate) vs. log (peak current), calculated from CV curves. (c) Capacitive contribution (shaded region) in CV curve (red line) of OMSCF-400 at the scan rate of 1 mV s-1. (d) Capacitive (grey) and diffusion-controlled contribution to Na-ion charge storage at different scan rates.

Fig. 6. (a) Charge-discharge curves of OMSCF-400//Na3V2(PO4)2F3 full cell during the first three cycles at 0.05 A g-1. (b) Cycling performance of OMSCF-400//Na3V2(PO4)2F3 full cell at 0.05 A g-1.

Fig. 7. (a) XRD pattern, (b) SEM, (c) TEM and (d) HRTEM images of the OMSCF-400 electrode after 60 cycles at a current density of 0.1 A g-1 charged to 3 V.

30


Page 30 of 38

Page 31 of 38 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


a

c

b

e

Carbon fibers

f

d

Carbon fibers

MoS2 MoS2

h

i

j

(002)

100nm

Fig. 1.

31


g


Intensity ( a.u.)

▼

★

●

★ ▼

★

b

MoO2 ★ MoO3 ●

● ●

OMSCF-500 ▼

13.1

OMSCF-400 14.1

OMSCF-300 MSCF

B2g B1g A 1g

OMSCF-300

OMSCF-400

528

600 900 1500 2000 -1 Raman shift (cm )

eS 2p

530 532 534 Binding Energy (eV)

536

162.2(S-Mo) 163.4(C-S)

162 164 Binding Energy (eV)

225

228 231 234 Binding Energy (eV)

237

f 120

OMSCF-400

160

OMSCF-400

MSCF

MSCF

MSCF

4+

232.6 (Mo (3d3/2)) 4 229.4 (Mo + (3d5/2)) 6+ 235.9 (Mo (3d3/2)) 226.6 (Mo-S)

Mo 3d

MSCF

300

Intensity (a.u.)

531.4(C-O) 532.6(Mo-O)

O 1s

OMSCF-500

OMSCF-400

10 20 30 40 50 60 70 80 2θ (degree)

d

c

D G

E12g

Intensity (a.u.)

2

★

166

Fig. 2.

32


Weight Percentage(%)

▼ MoS

●

Intensity (a.u.)

a

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 38

95%

100

85%

80 60 40 20 0

OMSCF-500 OMSCF-400 OMSCF-300 MSCF C@rGO

80%

76%

6%

100 200 300 400 500 600 700 o Temperature ( C)

a

2

40

-1

MSCF: 33.8 m g

2

-1

2

-1

OMSCF-300: 32.9 m g

400

OMSCF-400: 32.7 m g

300

2

-1

OMSCF-500: 153.2 m g

200 100

Solid: desorption Hollow: adsorption

0

MSCF: 18.9 nm OMSCF-300: 18.2 nm OMSCF-400: 19.1 nm OMSCF-500: 15.8 nm

b

32 dVp/drp (m3g-1nm-1)

500

dVp/drp (m3g-1nm-1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Quantity Adsorbed (cm3 g-1)

Page 33 of 38

24 16 8

30 20 10 0 0

5 10 15 Pore diameter (nm)

0 0.0

0.2 0.4 0.6 0.8 Relative pressure (P/P0)

1.0

0

10

Fig. 3.

33


20 30 40 50 Pore diameter (nm)

60

1.0

1st 2nd 3rd

-1.0 -1.5

400 300

0.2

0.3

0.5

e

-1

OMSCF-500 OMSCF-400 OMSCF-300 MSCF

@A g

1

200 100 0 0

g 8000

10

20 30 40 Cycle number

300

6000

0 0

100 40 60 80 Cycle number

OMSCF-400

1000

100

after 5 cycles after 10 cycles after 100 cycles


0

2000

A

Re

4000 6000 Z' (ohm)

8000

Cdl W

Rct 500

B

Cf

Cdl

Re 4

5

6

7

ω

-1/2

8

9

10

0 0

100

MSCF OMSCF-300 OMSCF-400 OMSCF-500

i

5000 3

20

f

200

h 1500

7000

150

-1

20

-1

0.1 A g

300

1Ag

0 0

50

MSCF OMSCF-300 OMSCF-400 OMSCF-500



450

150 300 450 600 750 -1 Specific capacity (mAh g )

-1

0.2

600

1st 2nd 3rd

400

Capacity (mAh g

500

-Z" / ohm

Capacity (mAh g-1)

d

0.0 0.5 1.0 1.5 2.0 2.5 3.0 Voltage (V)

750

-Z" (ohm)

0.0 -0.5

2.5 2.0 1.5 1.0 0.5 0.0 0

c

Capacity (mAh g )

0.5

Voltage (V)

) -1

Current (A g

b 3.0

-1

0.05 mV s

)

a

Z' (ohm)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 38

-1


W

500 1000 Z' / ohm

Fig. 4.

34


1500

Rf

Rct

10000

Page 35 of 38

b

0.6 0.4 0.2 0.0 -1

0.2 mV s -1 0.4 mV s -1 0.6 mV s -1 0.8 mV s -1 1.0 mV s

-0.2 -0.4

-0.6 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Voltage (V)

d

0.6

Contribution ratio (%)

c

0.4 0.2 0.0

73.0%

-0.2 -1

1.0 mV s

-0.4 -0.6 0.0

0.5

1.0

1.5

2.0

2.5

3.0

log (peak current / mA)

Current (mA)

a

Current (mA)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.8 0.6 0.4

-1

0.2 -0.8

140 120 100 80 60 40 20 0

Voltage (V)

Reduction Peak Oxidation Peak Reduction Peak: 0.71 Oxidation Peak: 0.80

Sweep rate: 0.2-1.0 mV s

-0.6 -0.4 -0.2 0.0 -1 log(aweep rate / mV s ) Diffiusion Capacitive

62.7%

54.8%

0.2

66.7%

69.7% 73.0%

0.4 0.6 0.8 1.0 -1 Scan rate (mV s )

Fig. 5.

35



a

500

b -1

Capacity (mAh g )

3.5 Voltage (V)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

3.0 2.5 2.0

1st 2nd 3rd

1.5 0

100

200 300 400 -1 Capacity (mAh g )

Page 36 of 38

500

400 300 200 Charge Discharge

100 0 0

Fig. 6.

36


5

10 15 Cycle number

20

Page 37 of 38

a Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


b S S S

MoS2

S

Mo MoS2

10 20 30 40 50 60 70 80 90 2θ (degree)

d

c

Fig. 7.

37



Table of Contents

750

MoS2

-1

Carbon fibers

Capacity (mAh g )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 38


600 450

-1

0.1 A g

300 150 0 0

20

38



100

Vertically Oxygen-Incorporated MoS2 Nanosheets Coated on Carbon

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