High Areal Capacitance for Lithium Ion Storage Achieved by a

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A High Areal Capacitance for Lithium Ions Storage Achieved by a Hierarchical Carbon / MoS2 Aerogel with Vertically Aligned Pores Peng Zhang, Yuqing Liu, Yan Yan, Yang Yu, Qinghong Wang, and Mingkai Liu ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.8b00897 • Publication Date (Web): 20 Aug 2018 Downloaded from http://pubs.acs.org on August 25, 2018

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ACS Applied Energy Materials

A High Areal Capacitance for Lithium Ions Storage Achieved by a Hierarchical Carbon / MoS2 Aerogel with Vertically Aligned Pores

Peng Zhang, Yuqing Liu, Yan Yan,* Yang Yu, Qinghong Wang and Mingkai Liu*

School of Chemistry & Materials Science, Jiangsu Key Laboratory of Green Synthetic Chemistry for Functional Materials, Jiangsu Normal University, Xuzhou 221116, China. E-mail: [email protected]; [email protected].

Abstract Developing high energy density electrode materials is of great importance for the practical applications of lithium ion batteries (LIBs). Here, an integrated vertically aligned carbon / MoS2 aerogel (VA-C/MoS2) with oriented pores has been developed. Vertically aligned pores ensure fast transportation of electrons and rapid penetration of electrolyte, meanwhile decreasing the transfer resistance of ions in this VA-C/MoS2 anode. The good electrical conductivity of three-dimensional (3D) carbon matrix with inter-connected microstructures, coupling with the homogeneously anchored MoS2 nanoflakes, promotes that all the active sites of MoS2 can be exploited during the electrochemical process. Due to these structural features of VA-C/MoS2 aerogel, an excellent specific capacity of 1089 mAh/g, a high rate capability and a long-term cycling stability up to 1000 cycles have been simultaneously achieved. Importantly, the areal capacity achieved by VA-C/MoS2 aerogel (12.4 mAh/cm2) based on a high mass loading of MoS2 (16 mg/cm2) is 10-fold increase compared with the result of 1

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pure MoS2 aggregations (1.24 mAh/cm2). These structural advantages and the excellent electrochemical performances permit VA-C/MoS2 aerogel to be a good candidate for LIBs, and can provide new insights for developing new high-energy materials for energy storage applications.

Keyword: Carbon / MoS2 aerogel, vertically aligned pores, high rate capability, high areal capacity, lithium ion battery

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1. Introduction Recently, lithium-ion batteries (LIB) have been considered as one of the most predominant batteries with the increasing requirements of clean and sustainable energy storage systems.1-4 However, state-of-the-art LIBs with low energy and power densities cannot meet the rising demand of portable electronics and electric vehicles (EVs).5-7 Commercial LIBs usually employ conventional LiCoO2 and traditional graphite as the cathode and anode materials, which exhibit low theoretical specific capacities of ~ 274 mAh/g (LiCoO2) and ~ 372 mAh/g (graphite), respectively. And the low density of graphite anode (~ 2 mg/cm3) results in poor volumetric and areal capacity, which further limits their wide applications, especially in the fields that require high energy with small size.8 Many metal oxide and sulfides materials with nanoscale / microscale morphologies have been developed as potential alternative anode materials to improve the lithium ion storage capabilities of LIBs.9-13 Among these newly developed anode materials, molybdenum disulfide (MoS2), a typical layered transition metal dichalcogenide (TMD),14-19 has been considered as one of the most promising energy-related candidates.20-24 The reaction mechanism between MoS2 and lithium ion are based on the following reaction: MoS2 + 4Li+ + 4e- → 2Li2S + Mo, which allows the successful intercalation of lithium ions due to the van der Waals gap between MoS2 layers.25-27 Nevertheless, low electrical conductivity and large volumetric change of active MoS2 materials during the charging / discharging process can result in their poor cycling stability, which becomes bottleneck for the practical applications of MoS2-based LIBs. 3



Combining MoS2 with carbon matrix (graphene sheets, carbon nanotubes, and so on) has been proven to be a rational approach for fabricating high performance MoS2-based anode materials with high specific capacity and good rate capability.28-32 MoS2 nanoflakes coated on three-dimensional (3D) carbon nanotubes via a magnetron sputtering method ensure high charge transfer ability and further exhibit outstanding cycling stability and high capacity, as well as good rate capability.33 Monolayer MoS2-graphene hybrid aerogel with controllable porosity was developed by Zeng group based on a hydrothermal method, which exhibits a high reversible capacity up to 1200 mAh/g at 0.1 A/g.34 However, the areal capacities of most reported MoS2-based materials are limited, which cannot meet the practical needs of high-energy devices. Meanwhile, the additionally added polymeric binders and conductive additions further increase the redundant weight of the anode and increase the inner electrical resistance of the assembled battery. Furthermore, the large volumetric expansion of active MoS2 will inevitably result in structural collapse in the anodic electrode, which causes continuous capacity fading during long-term cycling process. Thus, developing free-standing MoS2-based active anode materials with excellent electrical conductivity and good expansion space, meanwhile achieving high areal capacity, high specific capacity and good cycling stability is of urgent and great importance for the practical applications of LIBs. In this work, a 3D carbon / molybdenum disulfide (C/MoS2) hierarchical aerogel (VA-C/MoS2) with vertically aligned pores has been developed with MoS2 nanoflakes homogeneously anchored on the surface of aligned carbon pores. Compared with the 4


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aggregated structures of pure MoS2, all the active sites of the MoS2 nanoflakes in this VA-C/MoS2 aerogel can be exposed to the electrolyte and lithium-ions. Good conductive network of the carbon matrix can greatly decrease the interfacial contacting resistance by facilitating the rapid transfer of electrons and promoting the migration of ions. Moreover, vertically aligned pores created in this VA-C/MoS2 aerogel anode ensure fast penetration of electrolyte which can contribute to the good rate performance of the assembled LIBs. Due to these unique structural characteristics of VA-C/MoS2, extraordinary electrochemical performances of VA-C/MoS2 aerogel have been achieved, including a specific capacity of 1089 mAh/g, high rate capability, ultra-long term cycling stability up to 1000 times with a capacity retention of 90.6%. More importantly, a high areal capacity of 12.4 mAh/cm2 of VA-C/MoS2 aerogel based on a high areal mass loading of MoS2 (16 mg/cm2) has been achieved, which is 10-fold increase compared to the results for pure MoS2. These promising performances ensure VA-C/MoS2 to be one of the most competitive candidates for the high energy density LIBs.

2. Experimental section 2.1 Materials and preparation of poly(amic acid) (PAA) Graphite powders were purchased from Sigma-Aldrich (200 mesh). Graphene oxide sheets were prepared according to a modified Hummers' method.35 Hexaammonium

molybdate

((NH4)6Mo7O24),

Triethylamine

(C6H15N,

TEA),

N,N-dimethylacetamide (DMAc), Thiourea (CH4N2S), were purchased from 5



Sinopharm Chemical Reagent Co., Ltd. All chemicals were of analytic grade and used as received. PAA polymer was synthesized by 4,4'-oxidianiline (ODA), and pyromellitic dianhydride (PMDA) at 0 °C. Typically, 4.31 g of ODA was added into DMAc (55 mL) under strong mechanical stirring. Then, 4.69 g of PMDA was gradually added into the solution and reaction was maintained for 5 h at 0 °C. Afterwards, 2.18 g of TEA was dropped into the mixture and the reaction solution was further stirred for 8 h. The obtained TEA-capped poly(amic acid) (TEA-PAA) with a yellow color can be washed with deionized water for at least 5 times following by a treatment of freeze-drying, resulting in the preparation of PAA powders. 2.2 Synthesis of VA-C/MoS2 aerogel Firstly, graphene oxide sheets (2 mg/mL, 100 mL) were co-dispersed with PAA chains (1 g) with the assistant of TEA under strong sonication. The mixture was directionally freezed by immersing the bottom of the container into liquid nitrogen. Then the product was freeze-dried under 10 Pa at -50 °C following by being treated with a carbonization process of 900 °C for 2h, resulting in the formation of carbon matrix with vertically aligned pores. Interfacial anchoring of MoS2 nanoflakes on the surface of carbon matrix was realized via a hydrothermal process. (NH4)6Mo7O24 (2.47 g) and thiourea (2.131 g) were dispersed in ultra-pure water (60 mL), as well as 40 mg of the carbon matrix. The hydrothermal reaction was carried out at 180ºC for 12 h with an increasing rate of 2 ºC/min. The produced product was further treated at 500 ºC for 2h in Ar, resulting in the formation of VA-C/MoS2 aerogel. Here, pure MoS2 spheres were prepared with the same process without the addition of carbon 6


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matrix. 2.3 Materials characterization Structures and morphologies of the prepared samples were observed based on a field-emission scanning electron microscopy (SEM, SU8010, Hitachi) with an acceleration voltage of 5 kV. Energy dispersive spectroscopy (EDS) analysis was carried out with an EDAX equipment (PW9900) with an acceleration of 20 kV. Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) observations were performed with Tecnai G2 F20 (FEI, America) under an acceleration voltage of 200 kV. XRD patterns were detected by a Bruker D8 (Advanced, Germany) with Cu Kα radiation (λ = 0.1542 nm). TGA analysis was carried out on TA 50 from room temperature to 900 °C. X-ray photoelectron spectra (XPS) were acquired on an ESCALAB MK II equipment with Mg Kα as the excitation source. 2.4 Electrochemical measurements The electrochemical performances of VA-C/MoS2 aerogel were evaluated using a two-electrode coin cell with VA-C/MoS2 aerogel as the working electrode and pure lithium foil as the counter electrode. A typical polypropylene film (Celgard 2400) was used as a separator. 1 M mixed solution of lithium hexafluorophosphate (LiPF6) salt with a 1:1:1 mixture (volume ratio) solvent of diethylene carbonate (DEC), dimethylene carbonate (DMC) and ethylene carbonate (EC) was used as the electrolyte. The coin cells were assembled in an Ar-filled glovebox (Mikrouna) with humidity (H2O) and oxygen (O2) less than 0.1 PPM. Cyclic voltammetry (CV) curves 7



were obtained from an ARBIN equipment (5V/5mA, 32 channels) at room temperature in a voltage window of 1.8 - 3.0 V vs. Li+/Li. Discharge/charge analysis was carried out based on LAND 2001A systems. Electrochemical impedance spectroscopy (EIS) was carried out by a CHI 660D electrochemical station from 0.01 to 10 kHz with an AC amplitude of 0.5 mV. The working electrode of pure MoS2 were prepared by casting a slurry of 80 wt% pure MoS2 powders, 10 wt% super P, and 10 wt% polyvinylidenefluoride (PVDF) in N-methyl-2-pyrrolidone (NMP) on copper foil.

3. Results and discussion Figure 1 schematically illustrates the fabrication of VA-C/MoS2 aerogel with MoS2 nanoflakes homogeneously anchored on the surface of the carbon matrix. Firstly, graphene oxide sheets were thoroughly cross-linked by poly(amic acid) (PAA) molecule chains under intense stirring and strong sonication. The mixtures were directionally freezed by liquid nitrogen following by a freeze-drying treatment under vacuum less than 10 Pa at -50 °C. Carbon matrix with vertically aligned pores can be created by carbonization the freeze-dried product at 900 °C in Ar for 3 h. MoS2 sheets with nanoflake morphology were homogeneously deposited on the surface of the carbon matrix via a solvothermal process. These homogeneously deposited MoS2 nanoflakes coupling with the vertically aligned pores ensure large contact area between electrode materials and electrolyte, which will contribute to the outstanding electrochemical performances of the assembled LIBs. Figure S1 exhibits the digital 8


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photo of VA-C/MoS2 aerogel with a thickness of about 10 mm, which can be elastically compressed as a dense cake and directly used as a free-standing anode. Vertically aligned pores created in the carbon matrix can be confirmed by SEM images, as seen in Figure 2a. The cross-section structure of carbon matrix shows bottom-up aligned pores with an average pore size of 1 - 3 µm. The uniformly dispersed pores can be also observed from the top view of this carbon matrix, as seen in Figure S2. Good porous structures created throughout this carbon matrix ensure the rapid penetration of electrolyte as well as the fast transportation of lithium ions throughout this VA-C/MoS2 aerogel. Pure MoS2 materials prepared without the addition of carbon matrix exhibit heavily aggregated morphologies (Figure S3). Most MoS2 materials were internally packaged and cannot be fully exploited for insertion / deinsertion of lithium ions, leaving only the outside MoS2 layer can participate in the rapid electrochemical reactions. MoS2 nanoflakes can be homogeneously anchored on the surface of carbon matrix via a solvothermal treatment, as seen in Figure 2b - 2d. No aggregations can be observed from the cross-section of VA-C/MoS2 aerogel (Figure 2b), which confirms the result that interfacial deposition of MoS2 on the surface of this vertically aligned carbon pores can effectively prevent their aggregation tendency. SEM image at high magnification (Figure 2c) further demonstrates that MoS2 materials with nanoflake morphologies were homogeneously and densely deposited on the carbon shells. A fractural morphology of the VA-C/MoS2 aerogel confirms that MoS2 nanoflakes were tightly anchored on both sides of the carbon shells (Figure 2d). Detailed microstructures of the anchored MoS2 nanoflakes 9



were also observed (inset in Figure 2d). A great number of pores were coexisted with the MoS2 nanoflakes, which can provide sufficient expansion space for the volumetric change of the active MoS2 during the lithiation reaction process and ensure the thoroughly interfacial contact between the active sites of MoS2 and the lithium ions. The continuously aligned pores coupling with the well-dispersed MoS2 nanoflakes andow a high specific surface area of 189 m2/g, as seen in Figure S4. TEM image at low magnification shows the overlayer structure of VA-C/MoS2 aerogel, as seen in Figure 2e. Strong adhesion between MoS2 nanoflakes and the 3D carbon matrix can be observed. And no aggregation of MoS2 can be found in this VA-C/MoS2 aerogel, indicating the uniform dispersion of MoS2 nanoflakes on the surface of the carbon matrix. TEM image of VA-C/MoS2 aerogel at high magnification (Figure 2f) shows the formation of layered MoS2 nanoflakes with inter-planar spacing of 0.62 nm, which corresponds to the (002) lattice plane (2θ = 14.3°) of the hexagonal MoS2 phase.36,37 Energy dispersive spectroscopy (EDS) was used to confirm the existence and uniform distribution of MoS2 nanoflakes in this VA-C/MoS2 aerogel, as seen in Figure 3. EDS mappings observed from the selected cross-section of VA-C/MoS2 aerogel (Figure 3a) exhibit feeble carbon (C) detections (Figure 3b), because the carbon shells were completely covered by a homogeneous layer of MoS2 nanoflakes, which can be confirmed by the intense element signal of sulfur (S) (Figure 3c) and molybdenum (Mo) (Figure 3d). The obtained energy spectrum (Figure 3e) further indicates the co-existence of C, S and Mo elements. Furthermore, a high weight percent up to 89.4% for MoS2 was observed in VA-C/MoS2 aerogel (inset in Figure 3e). The porous 10


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structures of the deposited MoS2 nanoflakes, coupling with such a high weight content, will positively contribute to the high energy density of the assembled LIBs. Figure 4a exhibits the XRD patterns of carbon matrix, pure MoS2 and VA-C/MoS2 aerogel. Carbon matrix exhibits a broad diffraction peak at about 25.9°, which can be ascribed to the (002) diffraction peak of carbon-based materials.38 Pure MoS2 presents conspicuous characteristic peaks at 13.6º, 33º and 58.5º, which can be indexed as the (002), (100) and (110) planes of hexagonal MoS2 (JCPDS No. 171492).39-43 VA-C/MoS2 aerogel exhibits similar XRD patterns as that of pure MoS2, confirming the successful hybridization of MoS2 nanoflakes with the carbon matrix. While, the absence of carbon diffraction peak in the XRD patterns of VA-C/MoS2 aerogel can be attributed to the low content of carbon matrix and the intense diffraction intensity of anchored MoS2 nanoflakes. TGA measurement of VA-C/MoS2 aerogel was carried out in air from room temperature to 900 ºC, as seen in Figure 4b. Carbon materials can be oxidized to CO2 (stage II) and MoS2 was oxidized to MoO3 (stage III). The content of MoS2 in this VA-C/MoS2 aerogel was approximately 89.4 wt.%. X-ray photoelectron spectroscopy (XPS) analysis was further utilized to detect the chemical state of VA-C/MoS2 aerogel. The survey spectrum apparently shows the existence of Mo, C, and S elements, as seen in Figure 4c. Two peaks located at 229.4 and 232.7 eV that observed from the high-resolution Mo 3d spectrum (Figure 4d) can be assigned to Mo5/2 and Mo3/2 of the MoIV state, respectively.44-46 The weak peak observed at 226.6 eV in high-resolution Mo 3d spectrum was indexed to S 2s. S 2p spectrum can be divided into S 3p3/2 (162.2) and S 3p1/2 (163.7), as seen in Figure 4e, indicating that 11



the prepared materials are stoichiometric MoS2 products.47 Moreover, high-resolution C 1s spectrum (Figure 4f) shows diminished peaks at 286.7 and 289.2 eV that related to the oxygen-containing groups (C=O / C-O), which means the recovery of the conjugated structure of carbon matrix under high temperature treatment. This result can be further confirmed by the closed circuit with carbon matrix alternating the copper wire (Figure S5) due to its high electrical conductivity (64 S/cm). Cyclic voltammogram (CV) curves of LIBs with VA-C/MoS2 aerogel anode at the 1st, 2nd and 5th cycles have been presented, as seen in Figure 5a. Two prominent peaks at 0.9 and 0.3 V vs. Li+/Li can be observed during the first discharge process. The voltage peak at 0.9 V is due to the intercalation of lithium ion into the interlayer spacing of MoS2, resulting in the formation of LixMoS2.48 The peak at 0.3 V vs. Li+/Li can be ascribed to the characteristic conversion reaction from LixMoS2 to Li2S and Mo/Lix.49,50 In the anodic sweep, a broad peak at 1.7 V vs. Li+/Li and a sharp peak at 2.4 V vs. Li+/Li were observed. Here, the broad peak at 1.7 V vs. Li+/Li is associated with the reduction removal of lithium ions from Mo,51,52 and the peak at 2.4 V vs. Li+/Li is due to the oxidation of Li2S into sulfur.53,54 In the second cycle, a broad peak at 1.8 V vs. Li+/Li indicates the multi-step reaction mechanism of elemental sulfur with lithium and finally forming Li2S product.55,56 The other two catholic peaks detected at 1.0 V and 0.3 V vs. Li+/Li can be attributed to the insertion of lithium ions into the defect sites of MoS2 and lithium element association with Mo, respectively.57 The CV curves at the 2nd and 5th cycles are almost overlapped, confirming the stable kinetics of electrochemical reactions occurred in the VA-C/MoS2 aerogel anode. Pure 12


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MoS2 anode exhibits the similar cathodic and anodic peaks with lower current intensity (Figure S6), which was resulted from its lower lithium ion storage ability compared with VA-C/MoS2 aerogel. Discharge / charge curves of VA-C/MoS2 aerogel at the 1st, 2nd and 5th cycles were presented in Figure 5b. Two distinct plateaus at 1.1 and 0.6 V vs. Li+/Li can be observed in its first discharge profile. These two potential plateaus are due to the intercalation of lithium ion in the interlayer spacing of MoS2 that accounted for 1.8 Li+ intake and the conversion reaction which takes about 4 Li+, respectively.58 Whereas, one dominating plateau at about 2.3 V vs. Li+/Li in the charge curve was observed, which is consistent with the anodic peak at 2.4 V detected from the CV curves. A stable specific capacity of 1089 mAh/g of VA-C/MoS2 aerogel at 0.1 A/g can be obtained from its almost overlapped discharge curves on the 2nd and 5th cycles (Figure 5b). However, pure MoS2 exhibits a small specific capacity of 710 mAh/g at 0.1 A/g (Figure 5c), which may be resulted from the low utilization efficiency of active sites of MoS2 nanoflakes due to the aggregated morphology. Rate capability is an important criterion for LIB anode materials. Here, galvanostatical tests of VA-C/MoS2 aerogel and pure MoS2 at various current densities have been conducted, as seen in Figure 5d. An initial specific capacity of 1085 mAh/g can be obtained for VA-C/MoS2 aerogel, and high capacities of 891, 800, 759, 702 mAh/g can be achieved when the current density was increased to 0.5, 1.0, 2.0 and 5.0 A/g, respectively. Furthermore, a high specific capacity of 1045 mAh/g can be also achieved when the current density was recovered to 0.1 A/g with an average Coulombic efficiency of about 100%. For comparison, the pure MoS2 materials 13



exhibit interior rate performance with a much lower capacity of 189 mAh/g maintained when the current density was increased to 5.0 A/g. Moreover, the capacity of pure MoS2 was gradually decreased to 388 mAh/g on the 50th cycle although its specific capacity can be backed to 505 mAh/g when the current density was turned back to 0.1 A/g. The good rate capability of VA-C/MoS2 aerogel can be further confirmed by its stable discharge / charge curves at different current densities from 0.1 to 5.0 A/g, as shown in Figure 5e. Electrochemical impedance spectroscopy (EIS) of VA-C/MoS2 aerogel and pure MoS2 anodes have been conducted in order to further understand the improved specific capacity and the superior rate capability of VA-C/MoS2 aerogel. Nyquist plots of VA-C/MoS2 aerogel and pure MoS2 anodes, coupling with the equivalent circuit, have been presented in Figure 5f. Both the EIS curves of VA-C/MoS2 aerogel and pure MoS2 anodes present a semicircle in the high to medium frequency region, which can be ascribed to the charge-transfer resistance (Rct) at the interface between the electrolyte and the electrode.34 Meanwhile, the slops deserved at low frequency were due to the Warburg-type (Wo) resistance caused by ion diffusion inside the active electrode.59 Z-View software was used for modeling the Nyquist plots, and a created equivalent electrical circuit has been provided, as inset in Figure 5f. Here, Rs and RSEI donate the ohmic resistance including the electrolyte / electrode resistances,60 and the resistance of lithium ion migration through the SEI membrane,61 respectively. It can be clearly seen that the VA-C/MoS2 aerogel exhibits a much smaller radius of semicircle than that of pure MoS2, which corresponds to the much lower 14


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charge-transfer resistance of VA-C/MoS2 aerogel (50.5 Ω) compared with the result of pure MoS2 (106.7 Ω), as seen in Table S1. Long-term cycling performances of VA-C/MoS2 and pure MoS2 anodes at 5A/g were tested, as seen in Figure 5g. These two electrodes were firstly activated at a low current density of 0.5 A/g before long-term cycling. Pure MoS2 electrode exhibits a specific capacity of 412 mAh/g with a sharp decrease of its specific capacity from 20 to 50 cycles (Figure S7). And a low specific capacity of 96 mAh/g of pure MoS2 was obtained after being cycled for 1000 times, resulting in a poor capacity retention of 23.3%. Whereas, the cycling performance of VA-C/MoS2 aerogel was greatly improved with a high specific capacity of 613 mAh/g was achieved after 1000 cycles, which indicates that a great capacity retention (90.4%) of its initial specific capacity (678 mAh/g) was achieved. Also, an average Coulombic efficiency up to 100% has been achieved for this VA-C/MoS2 aerogel, indicating an excellent insertion / extraction equilibrium of lithium ions throughout the VA-C/MoS2 anode. In addition, the morphology of VA-C/MoS2 aerogel after being cycled for 1000 times is provided, as seen in Figure 5h and Figure S8. It can be seen, the vertically aligned pores were completely preserved with MoS2 nanoflakes tightly anchored on the surface of the carbon matrix. In addition, TEM images at low and high magnifications of the cycled VA-C/MoS2 anode show the integated structures of the carbon matrix and the MoS2 sheets, as well as the perserved crystal structures (Figure S9). The good structural stabiligy of VA-C/MoS2 aerogel can also undoubtedly contribute to the long-term cycling life. Moreover, the long-term cycling stabiilty of VA-C/MoS2 aerogel can be 15



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further confirmed by the stable CV curves in the first 100 cycles observed at 0.1 mV/s, as seen in Figure S10. The practical application of VA-C/MoS2 aerogel can be confirmed by a lit up (light emitting diode) LED with purple color (Figure 6a). Herein, the good cycling life and the excellent rate performance of VA-C/MoS2 aerogel can be ascribed to its excellent structural advantages. 3D carbon matrix with inter-connected morphologies permits fast transport of electrons, and the vertically aligned pores ensure rapid transportation of lithium ions and quick penetration of electrolyte, as illustrated in Figure 6b. Moreover, all the active sites of MoS2 nanoflakes can be effectively utilized due to the perfect porous structures of vertically aligned pores, which contribute to the high specific capacity of VA-C/MoS2 aerogel in the long-term cycling process. Also, the tightly anchored MoS2 nanoflakes with ultrathin morphology can shorten the diffusion paths of lithium ions, therefore improving the storage kinetics of lithium ions. Furthermore, the good electron transfer ability of the carbon matrix inhibits the pulverization of the active MoS2 nanoflakes, which resulted in the significantly improved cycling stability of VA-C/MoS2 anode. Nyquist plots of VA-C/MoS2 anode after being cycled for 1 and 1000 cycles have been provided, as seen in Figure S11. The limitedly increased Rct value after 1000 cycles (71.4 Ω) (Table S2) compared with the value after the 1st cycle (50.5) can further confirm the greatly improved cycling performance of VA-C/MoS2 aerogel. All these structural features constructively contribute to the outstanding lithium ion storage performances than other MoS2 based electrodes

including

MoS2-rGO/HCS,40

MoS2@C/CC,30

16


N-C@MoS2,44

and

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MS/PNFs,31 as illustrated in Figure 7.

4. Conclusion In summary, integrated VA-C/MoS2 aerogel with vertically aligned pores has been developed. Uniformly created vertically aligned pores permit rapid penetration of electrolyte and fast transportation of lithium ions throughout this VA-C/MoS2 anode. Good electrical conductivity of the carbon matrix and the uniform deposited MoS2 nanoflakes ensure all the active sites of MoS2 nanoflakes can be fully exploited during the electrochemical reactions. Furthermore, the good porous structures of VA-C/MoS2 aerogel and the microporous structures created beside the MoS2 nanoflakes provide sufficient space for the volumetric expansion of MoS2. Moreover, the tightly anchored MoS2 nanoflakes with ultrathin morphology can greatly shorten the diffusion paths of lithium ions, therefore improving the storage kinetics of lithium ions. Due to these structural features, a high specific capacity of 1089 mAh/g at 0.1 A/g has been achieved by VA-C/MoS2 aerogel, coupling with a good rate capability even at high current density of 5 A/g. Also, long-term cycling stability up to 1000 cycles with a high capacity retention of about 90.6% has been achieved by this VA-C/MoS2 aerogel. More importantly, a high areal capacity (12.4 mAh/cm2) of VA-C/MoS2 aerogel was obtained based on a mass loading of MoS2 (16 mg/cm2), which is 10-fold increase compared to the results for pure MoS2. Moreover, this VA-C/MoS2 aerogel can provide new sights for developing high energy density electrode materials with highly porous nanostructures. 17



ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: XXX. Digital photos, SEM images of the carbon matrix and pure MoS2 materials; TEM and SEM images of cycled electrode materials; BET results; Electrical conductivity of the carbon matrix; Additional electrochemical performances of pure MoS2 and VA-C/MoS2 aerogel. AUTHOR INFORMATION Corresponding Authors *(Mingkai Liu) E-mail: [email protected] *(Yan Yan) E-mail: [email protected] ORCID Mingkai Liu: 0000-0001-9060-848X Notes The authors declare no competing financial interest.

ACKNOWLEDGEMENTS This work was financially supported by the National Natural Science Foundation of China (51703087, 21601072, 51702138), PAPD, and Natural Science Foundation of Jiangsu Province (BK20150238, BK20170240).

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REFERENCES (1) Chen, Y. M.; Yu, X. Y.; Li, Z.; Paik, U.; Lou, X. W. Hierarchical MoS2 tubular structures internally wired by carbon nanotubes as a highly stable anode material for lithium-ion batteries. Sci. Adv. 2016, 2, e1600021. (2) Li, J.; Hou, Y.; Gao, X.; Guan, D.; Xie, Y.; Chen, J.; Yuan, C. A three-dimensionally interconnected carbon nanotube/layered MoS2 nanohybrid network for lithium ion battery anode with superior rate capacity and long-cycle-life. Nano Energy 2015, 16, 10-18. (3) Wang, G.; Zhang, J.; Yang, S.; Wang, F.; Zhuang, X.; Müllen, K.; Feng, X. Vertically Aligned MoS2 Nanosheets Patterned on Electrochemically Exfoliated Graphene for High-Performance Lithium and Sodium Storage. Adv. Energy Mater. 2018, 8, 1702254. (4) Luo, Y.; Zhang, Y.; Zhao, Y.; Fang, X.; Ren, J.; Weng, W.; Jiang, Y.; Sun, H.; Wang, B.; Cheng, X.; Peng, H. Aligned carbon nanotube/molybdenum disulfide hybrids for effective fibrous supercapacitors and lithium ion batteries. J. Mater. Chem. A 2015, 3, 17553-17557. (5) Zhu, C.; Mu, X.; van Aken, P. A.; Yu, Y.; Maier, J. Single-layered ultrasmall nanoplates

of

MoS2

embedded

in

carbon

nanofibers

with

excellent

electrochemical performance for lithium and sodium storage. Angew. Chem. Int. Ed. 2014, 53, 2152-2156. (6) Zhang, S.; Chowdari, B. V. R.; Wen, Z.; Jin, J.; Yang, J. Constructing Highly Oriented Configuration by Few-Layer MoS2: Toward High-Performance 19



Lithium-Ion Batteries and Hydrogen Evolution Reactions. ACS Nano 2015, 9, 12464-12472. (7) Wang, B.; Wu, Q.; Sun, H.; Zhang, J.; Ren, J.; Luo, Y.; Wang, M.; Peng, H. An intercalated graphene/(molybdenum disulfide) hybrid fiber for capacitive energy storage. J. Mater. Chem. A 2017, 5, 925-930. (8) Xu, Z.; Shen, X.; Zhang, Q.; Li, J.; Kong, L.; Cao, L.; Huang, J. Synthesis of Structurally Stable 3D MoS2 Architectures as High Performance Lithium-Ion Battery Anodes. Part. Part. Syst. Charact. 2016, 33, 311-315. (9) Xu, Z.; Wang, T.; Kong, L.; Yao, K.; Fu, H.; Li, K.; Cao, L.; Huang, J.; Zhang, Q. MoO2@MoS2 Nanoarchitectures for High-Loading Advanced Lithium-Ion Battery Anodes. Part. Part. Syst. Charact. 2017, 34, 1600223. (10) Zhao, X.; Sui, J.; Li, F.; Fang, H.; Wang, H.; Li, J.; Cai, W.; Cao, G. Lamellar MoSe2 nanosheets embedded with MoO2 nanoparticles: novel hybrid nanostructures promoted excellent performances for lithium ion batteries. Nanoscale 2016, 8, 17902-17910. (11) Cook, J. B.; Kim, H.-S.; Yan, Y.; Ko, J. S.; Robbennolt, S.; Dunn, B.; Tolbert, S. H. Mesoporous MoS2 as a Transition Metal Dichalcogenide Exhibiting Pseudocapacitive Li and Na-Ion Charge Storage. Adv. Energy Mater. 2016, 6, 1501937. (12) Chen, C.; Xie, X.; Anasori, B.; Sarycheva, A.; Makaryan, T.; Zhao, M.; Urbankowski, P.; Miao, L.; Jiang, J.; Gogotsi, Y. MoS2 ‐ on ‐ MXene Heterostructures as Highly Reversible Anode Materials for Lithium ‐ Ion 20


Page 20 of 37

Page 21 of 37 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


Batteries. Angew. Chem. Int. Ed. 2018, 57, 1846-1850. (13) Ren, W.; Zhang, H.; Guan, C.; Cheng, C. Ultrathin MoS2 Nanosheets@Metal Organic Framework-Derived N-Doped Carbon Nanowall Arrays as Sodium Ion Battery Anode with Superior Cycling Life and Rate Capability. Adv. Funct. Mater. 2017, 27, 1702116. (14) 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, 135, 17881-17888. (15) Xu, J.; Li, X.; Liu, W.; Sun, Y.; Ju, Z.; Yao, T.; Wang, C.; Ju, H.; Zhu, J.; Wei, S.; Xie, Y. Carbon Dioxide Electroreduction into Syngas Boosted by a Partially Delocalized Charge in Molybdenum Sulfide Selenide Alloy Monolayers. Angew. Chem. Int. Ed. 2017, 56, 9121-9125. (16) Zhang, X.; Xie, Y. Recent advances in free-standing two-dimensional crystals with atomic thickness: design, assembly and transfer strategies. Chem. Soc. Rev. 2013, 42, 8187-8199. (17) Jia, W.; Tang, B.; Wu, P. Nafion-assisted exfoliation of MoS2 in water phase and the application in quick-response NIR light controllable multi-shape memory membrane. Nano Res. 2017, 11, 542-553. (18) Gao, W.; Lee, Y. H.; Jiang, R.; Wang, J.; Liu, T.; Ling, X. Y. Localized and Continuous Tuning of Monolayer MoS2 Photoluminescence Using a Single Shape-Controlled Ag Nanoantenna. Adv. Mater. 2016, 28, 701-706. 21



Page 22 of 37

(19) Xu, S.; Li, D.; Wu, P. One-Pot, Facile, and Versatile Synthesis of Monolayer MoS2/WS2 Quantum Dots as Bioimaging Probes and Efficient Electrocatalysts for Hydrogen Evolution Reaction. Adv. Funct. Mater. 2015, 25, 1127-1136. (20) Yu, X. Y.; Hu, H.; Wang, Y.; Chen, H.; Lou, X. W. Ultrathin MoS2 Nanosheets Supported on N-doped Carbon Nanoboxes with Enhanced Lithium Storage and Electrocatalytic Properties. Angew. Chem. Int. Ed. 2015, 54, 7395-7398. (21) Wang, H.; Zhang, Q.; Yao, H.; Liang, Z.; Lee, H. W.; Hsu, P. C.; Zheng, G.; Cui, Y. High electrochemical selectivity of edge

versus terrace sites in

two-dimensional layered MoS2 materials. Nano Lett. 2014, 14, 7138-7144. (22) Xie, J.; Qu, H.; Xin, J.; Zhang, X.; Cui, G.; Zhang, X.; Bao, J.; Tang, B.; Xie, Y. Defect-rich MoS2 nanowall catalyst for efficient hydrogen evolution reaction. Nano Res. 2017, 10, 1178-1188. (23) Huang, Y.; Miao, Y. E.; Zhang, L.; Tjiu, W. W.; Pan, J.; Liu, T. Synthesis of few-layered MoS2 nanosheet-coated electrospun SnO2 nanotube heterostructures for enhanced hydrogen evolution reaction. Nanoscale 2014, 6, 10673-10679. (24) Xie, J.; Zhang, H.; Li, S.; Wang, R.; Sun, X.; Zhou, M.; Zhou, J.; Lou, X. W.; Xie, Y. Defect-rich MoS2 ultrathin nanosheets with additional active edge sites for enhanced electrocatalytic hydrogen evolution. Adv. Mater. 2013, 25, 5807-5813. (25) Jiao, Y.; Mukhopadhyay, A.; Ma, Y.; Yang, L.; Hafez, A. M.; Zhu, H. Ion Transport Nanotube Assembled with Vertically Aligned Metallic MoS2 for High Rate Lithium‐Ion Batteries. Adv. Energy Mater. 2018, 1702779. (26) Hwang, H.; Kim, H.; Cho, J. MoS2 nanoplates consisting of disordered 22


Page 23 of 37 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


graphene-like layers for high rate lithium battery anode materials. Nano Lett. 2011, 11, 4826-30. (27) 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. (28) Fan, X.; Gaddam, R. R.; Kumar, N. A.; Zhao, X. S. A Hybrid Mg2+/Li+ Battery Based on Interlayer-Expanded MoS2/Graphene Cathode. Adv. Energy Mater. 2017, 7, 1700317. (29) Fang, Y.; Lv, Y.; Gong, F.; Elzatahry, A. A.; Zheng, G.; Zhao, D. Synthesis of 2D-Mesoporous-Carbon/MoS2 Heterostructures with Well-Defined Interfaces for High-Performance Lithium-Ion Batteries. Adv. Mater. 2016, 28, 9385-9390. (30) Deng, Z.; Jiang, H.; Hu, Y.; Liu, Y.; Zhang, L.; Liu, H.; Li, C. 3D Ordered Macroporous MoS2@C Nanostructure for Flexible Li‐Ion Batteries. Adv. Mater. 2017, 29, 1603020. (31) Kong, J.; Zhao, C.; Wei, Y.; Lu, X. MoS2 Nanosheets Hosted in Polydopamine-Derived Mesoporous Carbon Nanofibers as Lithium-Ion Battery Anodes: Enhanced MoS2 Capacity Utilization and Underlying Mechanism. ACS Appl. Mater. Interfaces 2015, 7, 24279-24287. (32) Zhang, Y.; Mu, Z.; Yang, C.; Xu, Z.; Zhang, S.; Zhang, X.; Li, Y.; Lai, J.; Sun, Z.; Yang, Y.; Chao, Y.; Li, C.; Ge, X.; Yang, W.; Guo, S. Rational Design of MXene/1T-2H MoS2-C Nanohybrids for High-Performance Lithium-Sulfur 23



Batteries. Adv. Funct. Mater. 2018, 1707578. (33) Patel, M. D.; Cha, E.; Choudhary, N.; Kang, C.; Lee, W.; Hwang, J. Y.; Choi, W. Vertically oriented MoS2 nanoflakes coated on 3D carbon nanotubes for next generation Li-ion batteries. Nanotechnology 2016, 27, 495401. (34) Jiang, L.; Lin, B.; Li, X.; Song, X.; Xia, H.; Li, L.; Zeng, H. Monolayer MoS2-Graphene Hybrid Aerogels with Controllable Porosity for Lithium-Ion Batteries with High Reversible Capacity. ACS Appl. Mater. Interfaces 2016, 8, 2680-2687. (35) Yang, Z.; Deng, J.; Chen, X.; Ren, J.; Peng, H. A Highly Stretchable, Fiber‐ Shaped Supercapacitor. Angew. Chem. Int. Ed. 2013, 52, 13453-13457. (36) Dai, R.; Zhang, A.; Pan, Z.; Al-Enizi, A. M.; Elzatahry, A. A.; Hu, L.; Zheng, G. Epitaxial Growth of Lattice-Mismatched Core-Shell TiO2@MoS2 for Enhanced Lithium-Ion Storage. Small 2016, 12, 2792-2799. (37) Amiinu, I. S.; Pu, Z.; Liu, X.; Owusu, K. A.; Monestel, H. G. R.; Boakye, F. O.; Zhang, H.; Mu, S. Multifunctional Mo-N/C@MoS2 Electrocatalysts for HER, OER, ORR, and Zn-Air Batteries. Adv. Funct. Mater. 2017, 27, 1702300. (38) Xiong, F.; Cai, Z.; Qu, L.; Zhang, P.; Yuan, Z.; Asare, O. K.; Xu, W.; Lin, C.; Mai, L. Three-Dimensional Crumpled Reduced Graphene Oxide/MoS2 Nanoflowers: A Stable Anode for Lithium-Ion Batteries. ACS Appl. Mater. Interfaces 2015, 7, 12625-12630. (39) Zhang, X.; Li, X.; Liang, J.; Zhu, Y.; Qian, Y. Synthesis of MoS2@C Nanotubes Via the Kirkendall Effect with Enhanced Electrochemical Performance for 24


Page 24 of 37

Page 25 of 37 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


Lithium Ion and Sodium Ion Batteries. Small 2016, 12, 2484-2491. (40) Hu, X.; Li, Y.; Zeng, G.; Jia, J.; Zhan, H.; Wen, Z. Three-Dimensional Network Architecture with Hybrid Nanocarbon Composites Supporting Few-Layer MoS2 for Lithium and Sodium Storage. ACS Nano 2018, 12, 1592-1602. (41) Liu, Y.; He, X.; Hanlon, D.; Harvey, A.; Coleman, J. N.; Li, Y. Liquid Phase Exfoliated MoS2 Nanosheets Percolated with Carbon Nanotubes for High Volumetric/Areal Capacity Sodium-Ion Batteries. ACS Nano 2016, 10, 8821-8828. (42) Zhu, C.; Mu, X.; van Aken, P. A.; Maier, J.; Yu, Y. Fast Li Storage in MoS2-Graphene-Carbon Nanotube Nanocomposites: Advantageous Functional Integration of 0D, 1D, and 2D Nanostructures. Adv. Energy Mater. 2015, 5, 1401170. (43) Yang, J.; Wang, K.; Zhu, J.; Zhang, C.; Liu, T. Self-Templated Growth of Vertically Aligned 2H-1T MoS2 for Efficient Electrocatalytic Hydrogen Evolution. ACS Appl. Mater. Interfaces 2016, 8, 31702-31708. (44) Xie, D.; Xia, X.; Wang, Y.; Wang, D.; Zhong, Y.; Tang, W.; Wang, X.; Tu, J. Nitrogen‐Doped Carbon Embedded MoS2 Microspheres as Advanced Anodes for Lithium ‐

and Sodium ‐ Ion Batteries. Chem. Eur. J. 2016, 22,

11617-11623. (45) Zhang, Z.; Zhao, H.; Teng, Y.; Chang, X.; Xia, Q.; Li, Z.; Fang, J.; Du, Z.; Świerczek, K. Carbon-Sheathed MoS2 Nanothorns Epitaxially Grown on CNTs: Electrochemical Application for Highly Stable and Ultrafast Lithium Storage. 25



Adv. Energy Mater. 2018, 8, 1700174. (46) Li, H.; Yu, K.; Fu, H.; Guo, B.; Lei, X.; Zhu, Z. MoS2/Graphene Hybrid Nanoflowers with Enhanced Electrochemical Performances as Anode for Lithium-Ion Batteries. J. Phys. Chem. C 2015, 119, 7959-7968. (47) Wang, K.; Yang, J.; Zhu, J.; Li, L.; Liu, Y.; Zhang, C.; Liu, T. General solution-processed formation of porous transition-metal oxides on exfoliated molybdenum disulfides for high-performance asymmetric supercapacitors. J. Mater. Chem. A 2017, 5, 11236-11245. (48) Chao, Y.; Jalili, R.; Ge, Y.; Wang, C.; Zheng, T.; Shu, K.; Wallace, G. G. Self-Assembly of Flexible Free-Standing 3D Porous MoS2-Reduced Graphene Oxide Structure for High-Performance Lithium-Ion Batteries. Adv. Funct. Mater. 2017, 27, 1700234. (49) Liu, Y.; He, X.; Hanlon, D.; Harvey, A.; Khan, U.; Li, Y.; Coleman, J. N. Electrical, Mechanical, and Capacity Percolation Leads to High-Performance MoS2/Nanotube Composite Lithium Ion Battery Electrodes. ACS Nano 2016, 10, 5980-5990. (50) Hu, S.; Chen, W.; Uchaker, E.; Zhou, J.; Cao, G. Mesoporous Carbon Nanofibers Embedded with MoS2 Nanocrystals for Extraordinary Li-Ion Storage. Chem. Eur. J. 2015, 21, 18248-18257. (51) Sen, U. K.; Mitra, S. High-rate and high-energy-density lithium-ion battery anode containing 2D MoS2 nanowall and cellulose binder. ACS Appl. Mater. Interfaces 2013, 5, 1240-1247. 26


Page 26 of 37

Page 27 of 37 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


(52) Yang, J.; Zhu, J.; Xu, J.; Zhang, C.; Liu, T. MoSe2 Nanosheet Array with Layered MoS2 Heterostructures for Superior Hydrogen Evolution and Lithium Storage Performance. ACS Appl. Mater. Interfaces 2017, 9, 44550-44559. (53) Xiao, J.; Wang, X.; Yang, X. Q.; Xun, S.; 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. (54) Zhang, K.; Kim, H. J.; Shi, X.; Lee, J. T.; Choi, J. M.; Song, M. S.; Park, J. H. Graphene/acid coassisted synthesis of ultrathin MoS2 nanosheets with outstanding rate capability for a lithium battery anode. Inorg. Chem. 2013, 52, 9807-9812. (55) Teng, Y.; Zhao, H.; Zhang, Z.; Li, Z.; Xia, Q.; Zhang, Y.; Zhao, L.; Du, X.; Du, Z.; Lv, P.; Swierczek, K. MoS2 Nanosheets Vertically Grown on Graphene Sheets for Lithium-Ion Battery Anodes. ACS Nano 2016, 10, 8526-8535. (56) Hu, S.; Chen, W.; Zhou, J.; Yin, F.; Uchaker, E.; Zhang, Q.; Cao, G. Preparation of carbon coated MoS2 flower-like nanostructure with self-assembled nanosheets as high-performance lithium-ion battery anodes. J. Mater. Chem. A 2014, 2, 7862-7872. (57) Zhou, J.; Qin, J.; Zhang, X.; Shi, C.; Liu, E.; Li, J.; Zhao, N.; He, C. 2D Space-Confined Synthesis of Few-Layer MoS2 Anchored on Carbon Nanosheet for Lithium-Ion Battery Anode. ACS Nano 2015, 9, 3837-3848. (58)

Xu,

G.;

Yang,

L.;

Wei,

X.;

Ding,

J.;

27


Zhong,

J.;

Chu,

P.

K.


MoS2-Quantum-Dot-Interspersed

Li4Ti5O12

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Nanosheets

with

Enhanced

Performance for Li- and Na-Ion Batteries. Adv. Funct. Mater. 2016, 26, 3349-3358. (59) Miao, Z. H.; Wang, P. P.; Xiao, Y. C.; Fang, H. T.; Zhen, L.; Xu, C. Y. Dopamine-Induced Formation of Ultrasmall Few-Layer MoS2 Homogeneously Embedded in N-Doped Carbon Framework for Enhanced Lithium-Ion Storage. ACS Appl. Mater. Interfaces 2016, 8, 33741-33748. (60) Song, H.; Li, N.; Cui, H.; Wang, C. Enhanced storage capability and kinetic processes by pores- and hetero-atoms- riched carbon nanobubbles for lithium-ion and sodium-ion batteries anodes. Nano Energy 2014, 4, 81-87. (61) Song,

H.;

Shen,

L.;

Wang,

J.;

Wang,

C.

Phase

segregation

and

self-nano-crystallization induced high performance Li-storage in metal-organic framework bulks for advanced lithium ion batteries. Nano Energy 2017, 34, 47-57.

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Figure 1. Schematic illustration the fabrication process of VA-C/MoS2 aerogel with MoS2 nanoflakes homogeneously anchored on the vertically aligned pores.

29



Figure 2. SEM images of (a) cross section of carbon matrix, (b, c) cross section of VA-C/MoS2 aerogel at low and high magnifications, (d) fracture section of VA-C/MoS2 aerogel, inset shows the detailed morphology of MoS2 nanoflakes. Scale bar for inset image in (d) is 100 nm. TEM images of VA-C/MoS2 aerogel at (e) low and (f) high magnifications.

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Figure 3. (a) SEM image observed from the selected cross-section of VA-C/MoS2 aerogel, and corresponding EDS mapping images of (b) C, (c) S, and (d) Mo elements; (e) Energy spectrum of VA-C/MoS2 aerogel obtained from EDS detections.

31



Figure 4. (a) XRD patterns of carbon matrix, pure MoS2 and VA-C/MoS2 aerogel; (b) TGA observation of VA-C/MoS2 aerogel in air; (c) XPS survey of VA-C/MoS2 aerogel and high-resolution spectra of (d) Mo 3d, (e) S 2p and (f) C 1s.

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Figure 5. Electrochemical performances of VA-C/MoS2 aerogel and pure MoS2 as anode materials for LIBs: (a) CV curves for the 1st, 2nd and 5th cycles at 0.1 mV/s and (b) galvanostatic discharge / charge profiles at 0.1 A/g of VA-C/MoS2 anode; (c) Comparison of the discharge / charge curves of VA-C/MoS2 anode with that of pure MoS2 anode at the 10th cycle; (d) Rate performances of VA-C/MoS2 and pure MoS2 anodes with the Coulombic efficiencies of VA-C/MoS2 aerogel; (e) Different discharge / charge curves of VA-C/MoS2 aerogel at various rates from 0.1 to 5.0 A/g; (f) Nyquist plots of VA-C/MoS2 and pure MoS2 anodes at the full charge state (3.0 V) after 10 cycles; (g) Long-term cycling performances of VA-C/MoS2 anode at 5 A/g over 1000 cycles with a MoS2 mass loading of 16 mg/cm2; (h) SEM image of VA-C/MoS2 anode after being cycled for 1000 times. 33



Figure 6. (a) A purple LED can be lit up by the LIB with VA-C/MoS2 anode; (b) Schematic illustration the rapid insertion / desertion of lithium ions at large scale.

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Figure 7. Comparasion of the lithium ion storage performances of the VA-C/MoS2 aerogel and other electrode materials.

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The table of contents:

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An integrated carbon / MoS2 hybrid aerogel (VA-C/MoS2) with vertically aligned pores exhibits a high areal capacity of 12.4 mAh/cm2. 195x153mm (150 x 150 DPI)


High Areal Capacitance for Lithium Ion Storage Achieved by a

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