Nitrogen-Doped Carbon Composite

Research Article pubs.acs.org/journal/ascecg

Novel Amorphous MoS2/MoO3/Nitrogen-Doped Carbon Composite with Excellent Electrochemical Performance for Lithium Ion Batteries and Sodium Ion Batteries Kunjie Zhu,† Xiaofeng Wang,*,† Jun Liu,*,‡ Site Li,§ Hao Wang,† Linyu Yang,†,⊥ Sailin Liu,† and Tian Xie† †

School of Materials Science and Engineering, Central South University, 932 South Lushan Road, Changsha, Hunan 410083, China School of Materials Science and Engineering, Central South University, 932 South Lushan Road, Changsha, Hunan 410083, China § Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213 United States ⊥ School of Physics and Technology, Xin Jiang University, Urumqi, Xinjiang 830000, China ‡

S Supporting Information *

ABSTRACT: A novel amorphous MoS2/MoO3/nitrogendoped carbon composite has been successfully synthesized for the first time. The synthesis strategy only involves a facile reaction that partially sulfurizes organic−inorganic hybrid material Mo3O10 (C2H10N2) (named as MoOx/ethylenediamine) nanowire precursors at low temperature (300 °C). It is more interesting that such amorphous composites as lithium ion battery (LIB) and sodium ion battery (SIB) anode electrodes showed much better electrochemical properties than those of most previously reported molybdenum-based materials with crystal structure. For example, the amorphous composite electrode for LIBs can reach up to 1253.3 mA h g−1 at a current density of 100 mA g−1 after 50 cycles and still retain 887.5 mA h g−1 at 1000 mA g−1 after 350 cycles. Similarly, for SIBs, it also retains 538.7 mA h g−1 after 200 cycles at 300 mA g−1 and maintains 339.9 mA h g−1 at 1000 mA g−1 after 220 cycles, corresponding to a capacity retention of nearly 100%. In addition, the amorphous composite electrode exhibits superior rate performance for LIBs and SIBs. Such superior electrochemical performance may be attributed to the following: (1) The carbonaceous matrix can enhance the conductivity of the amorphous composite. (2) Heteroatom, such as N, doping within this unique compositional feature can increase the active ion absorption sites on the amorphous composite surface benefitting the insertion/extraction of lithium/sodium ions. (3) The hybrid nanomaterials could provide plenty of diffusion channels for ions during the insertion/extraction process. (4) The 1D chain structure reduces the transfer distance of lithium/sodium ions into/from the electrode. KEYWORDS: Amorphous, MoS2/MoO3, Lithium ions batteries, Sodium ion batteries

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INTRODUCTION In recent years, owing to the pollution problems and the fossil energy crisis on the earth, clean energy, especially the electrochemical energy storage system has attracted more and more attention.1 The core of the electrochemical energy system is various energy materials. Since their commercial application, lithium ion batteries (LIBs) have captured the market of mobile power supplies, greatly improving living standards.2 However, graphite as the commercial electrode material of LIBs only has a theoretical specific capacity of 372 mA h g−1, which is unsatisfactory to meet the requirements of electric vehicles.3 So researchers began to explore alternative materials to satisfy the needs of society, namely higher specific capacity, more stable cycle performance, higher initial discharge specific capacity, higher efficiency, and lower cost, etc.4−6 Based on this background, researchers mainly study various metal oxide © 2017 American Chemical Society

materials, metal sulfide materials, and metal selenide materials, etc.7−9 Under electrochemical reactions, these active materials suffer from the problems such as volume expansion and low conductivity, making their cycling stability very poor and limiting their practical application despite their much higher theoretical specific capacity than carbon materials.10,11 To overcome these shortcomings, researchers carry out massive efforts to improve the crystal structure stability and conductivity of active materials, such as element doping and surface coating.12,13 In consideration of the cost of electrochemical energy storage system, sodium ion batteries (SIBs) have attracted great attention owing to the abundance, wide Received: May 21, 2017 Revised: July 17, 2017 Published: August 11, 2017 8025

DOI: 10.1021/acssuschemeng.7b01595 ACS Sustainable Chem. Eng. 2017, 5, 8025−8034

Research Article

ACS Sustainable Chemistry & Engineering

stirring at room temperature until a white precipitate appeared (pH around 4−5). After a reaction at 50 °C for 2 h, the product was collected and washed several times with deionized water and then dried at 70 °C overnight. Synthesis of the Amorphous MoS2/MoO3/N-Doped C Composite. In a typical synthesis, thiourea was used as sulfur source. The as-prepared organic−inorganic hybrid material of MoOx/EDA nanowire was placed in a quartz boat, filled with thiourea. Subsequently, the sample was heated at 300 °C for 2 h under H2/ Ar flow (5% of H2) with a heating rate of 2 °C min−1, and then cooled to ambient temperature under argon. Characterization. The collected amorphous composite product were characterized by X-ray diffraction (XRD) on a Rigaku D/max 2500 XRD diffractometer (Cu−Kα radiation, λ = 1.15178 Å) and Raman spectroscopy (Jobin Yvon LabRAM Hr800, Longjumeau, France). Element content analysis (CHNSO) was conducted by an elemental analyzer (Vario Micro Cube, Elementar, Germany). The Xray photoelectron spectroscopy (XPS) experiments were carried out on an ESCALAB 250Xi System (ThermoFisher) equipped with a monochromatic Al Kα (1486.6 eV) source and a concentric hemispherical energy analyzer. A scanning electron microscope (SEM) was characterized using FEI Nova Nano SEM 230 scanning electron microscope. Transmission electron microscope (TEM JEOLJEM-2100) examination equipped with energy dispersive system (EDX) was used to investigate the structure of amorphous composite product. Electrochemical Measurements. The anode electrodes were prepared by mixing a-MM/NCc, conductive agent (Super P) and binder (PAA) together in a weight ratio of 7:2:1. Then the mixture was dissolved in deionized water and magnetically stirred for 24 h. Subsequently, the obtained slurry was coated on Cu foils, and then dried at 95 °C in vacuum oven for 12 h to evaporate the dispersants. The coin cells were laboratory-assembled by a CR2016 press in a glovebox (Mbraun, Germany) filled with ultrahigh purity argon. As for LIBs, polyethylene membrane was used as separator and lithium foil was used as the anode. The electrolyte used for LIBs was 1 M LiPF6 in ethylene carbonate (EC) and dimethyl carbonate (DMC) (1:1 in volume). As for SIBs, the glass microfiber filters was used as separator and sodium foil was used as the anode. The electrolyte used for SIBs was 1 M NaClO4 in ethylene carbonate (EC) and diethylcarbonate (DEC) (1:1 in volume) with 1% fluoroethylenecarbonate (FEC) as additive. The electrochemical measurements were conducted by a Land Battery Tester (Land CT 2001A, Wuhan, China) at room temperature. Cyclic voltammetry (CV) measurements were carried out on a Chi604e electrochemical workstation at a scan rate of 0.05 mV s−1.

distribution, and low cost of sodium resources. However, the radius of the sodium ion (1.02 Å) is larger than that of the lithium ion (0.69 Å), which means Na+ is more difficult to extract/insert from/in the electrode materials, further deteriorating the cycling performance and rate performance of the SIBs.14−16 Thus, searching for advanced active materials becomes one of the key factors of large-scale commercial application of LIBs/SIBs. Recently, molybdenum-based materials (such as MoO2, MoO3, MoS2, and MoSe2) are of great interest to researchers to synthesize a wide array of substances as electrochemical energy storage active materials. They show many desirable properties including good chemical stability and a high theoretical specific capacity. In practical studies, however, researchers have found that this kind of material is not as perfect as they expect, because their poor electrical conductivity and poor ions kinetics of diffusion reduce the cycle stability of the battery.17 To resolve these issues, molybdenum-based materials are incorporated with good electronic conductivity substrate to form hierarchical structure or synthesized as nanostructure to lessen the ions diffusion path lengths. For example, Yang et al. prepared ultrafine MoO2/graphene composites first used as anode materials for LIBs.18 Lu et al. adopted hydrothermal process to synthesize α-MoO3/graphene composites, which are able to retain a reversible specific capacity of up to 823 mA h g−1 after 70 cycles at 200 mA g−1 for LIBs.19 Noticeably, Xu et al. fabricated hybrid nanostructure of MoS2 nanosheet@TiO2 nanotube for LIBs anode material by four-steps.20 Yang et al. synthesized MoSe2 nanosheets@porous hollow carbon spheres for LIBs and SIBs anode materials by a three-step process.21 Although high cycling properties and rate performance for LIBs or SIBs are obtained by conductivity modification and synthesizing nanostructures of molybdenum-based materials, the complex synthetic procedure and low yield restrict their large scale application. Additionally, most of the reported molybdenum-based materials for LIBs/SIBs are highly crystalline, which are often synthesized under high temperature or high pressure. Therefore, it still remains a great challenge to explore a facile and low-temperature method to synthesize molybdenum-based materials with excellent electrochemical performance for LIBs/SIBs. In this work, a novel amorphous MoS2/MoO3/N-doped C composite (a-MM/NCc) has been successfully synthesized for the first time. Different from most of other reported active substances, the as synthesized substance is an amorphous composite due to the low-temperature reaction. Due to their unique architecture characteristics, the electrochemical test results show those amorphous composite materials have a high specific capacity, superior rate capability, and excellent cycling stability in both LIBs and SIBs. As was stated above, there are very few reports of amorphous material explored as LIBs or SIBs, so this work may contribute to further research.

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RESULTS AND DISCUSSION Structural Characterization. First, XRD was used to detect the phase purity and crystallinity of the precursors. As shown in Figure S1, the XRD patterns of the organic−inorganic hybrid material of Mo3O10(C2H10N2) can be assigned to the pure MoOx/EDA (JCPDS no. 00-058-1318) with no detected impurity.24 To examine the morphology of as-prepared organic−inorganic hybrid material MoOx/EDA, the SEM images were performed. From Figure S2, it can be clearly seen that the MoOx/EDA shows uniform wirelike morphology with lengths of about 10−50 μm and diameters of about several nanometers. In order to determine the final products, several different detection techniques were conducted. First, XRD detection method was used to detect the phase. From the XRD pattern of the final products in Figure 1, no obvious diffraction peaks can be observed and only two wider drums can be seen, indicating the as prepared materials are amorphous. Interestingly, according to previous literature reports, amorphous MoO3 has a wide drum at around 2θ = 10°, in agreement with the

EXPERIMENTAL SECTION

Synthesis of Organic−Inorganic Hybrid Material of Mo3O10(C2H10N2) Nanowire. All chemicals and solvents involved in this work were purchased from commercial sources and used without further purification. A method developed previously has been used to synthesize the organic−inorganic hybrid material Mo3O10(C2H10N2) nanowire.22−24 In a typical experiment, 1.24 g of (NH4)6Mo7O24·4H2O and 1.0 mL ethylenediamine (EDA) was dissolved in 15 mL of deionized water first, and then 1 M HCl aqueous solution was cautiously added, dropwise with magnetic 8026


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235.58 eV is for Mo (VI) (typical of MoO3).31,32 From Figure 2c, the S 2p3/2 peak at 162.0 eV and S 2p1/2 peak at 163.2 eV indicate the presence of S2−, with a binding energy typical of MoS2.25,26 From Figure 2d, the XPS O 1s core level spectrum is dominated by one peak at about 533.1 eV typical of O.2−33 From Figure 2e and 2, it can be observed that the binding energies of 285, 287.8, and 398.4 eV are typical of the C 1s, CO, and N 1s spectral lines of C−N, CO, and C−N in EDA, CO2, and EDA,34−36 where CO2 is from air and EDA is from the residual organic substance. Those observations are in agreement with previous reports.37−40 The composition of the amorphous composite could also be determined by Raman spectra as exhibited in Figure S3. Two characteristic bands of MoS2 are observed at 373.8 cm−1 (E12g) and 400.2 cm−1 (A1g).41,42 In addition, three typical peaks at 662, 816.3, and 990.9 cm−1 can be attributed to the asymmetrical stretching vibration of O−Mo−O bonds, the symmetric stretch of the terminal oxygen atoms and the asymmetric stretch of the terminal oxygen atoms, respectively.43,44 The broad peak in the range 1200−1500 cm−1 is attributed amorphous carbon.45 Those observations are in agreement with previous reports.46,47 Thus, considering these experimental results together, it can be eventually determined that the amorphous composite mainly consists of MoS2 and MoO3, namely MoS2/MoO3 (the mole ratio is 3:2). To further characterize the morphology and detailed structure of a-MM/NCc, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed. As shown in Figure 3a, the morphology of a-MM/ NCc is consistent with the organic−inorganic hybrid material of Mo3O10(C2H10N2) precursor, namely, uniform wirelike morphology. It should be noted that the former is shorter than the latter in length, which is caused by the subsequent heat treatment process. Figure 3b and c show the diameters of aMM/NCc are of around 450 nm. That is to say, the precursors have not become coarse in the subsequent heat treatment process and still maintained the morphology of 1D chain structure. Typical TEM images from Figure 4a intuitively reveal the morphology of a-MM/NCc is 1D wirelike, in agreement with the SEM results. From Figure 4b, the HRTEM images also demonstrate that the products are amorphous, which is consistent with XRD results. Besides, the EDX analysis results

Figure 1. X-ray diffraction (XRD) patterns of the amorphous composite.

former drum in Figure 1.25 Similarly, amorphous MoS2 has a wide drum between 30° and 50°, which corresponds to the latter drum in Figure 1.26−28 Then, the element content analysis (CNOSH) and ICP-OES were used to detect the element content of the products. The results are shown in Table 1. It can be seen the products mainly contain Mo, S, O, Table 1. Results of the Element Content Analysis (CNOSH) and ICP-OES element

Mo

S

O

C

N

wt percent wt percent (theoretical)

47.87 49.87

20.56 20.01

10.99 9.98

9.34 9.34

10.80 10.80

C, and N elements. For further determining the valence state of each element, XPS test was conducted on the products as exhibited in Figure 2a. The peaks of Mo 3d, S 2p, O 1s, C 1s, and N 1s can be clearly seen, corresponding to the product of element content analysis (CNOSH) and ICP-OES. From Figure 2b, the binding energies of Mo (3d5/2) and Mo (3d3/2) in the composite are observed at 229.7 and 232.46 eV, respectively, which are attributed to Mo (IV) (typical of MoS2).29,30 Simultaneously, XPS (Figure 2b) showed peak at

Figure 2. XPS spectra for the amorphous composite: (a) survey spectrum and the high-resolution spectra of (b) Mo 3d, (c) S 2p, (d) O 1s, (e) C 1s, and (f) N 1s. 8027


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Figure 3. SEM images of the amorphous composite.

Figure 4. (a) TEM images of the amorphous composite. (b) HRTEM images of the amorphous composite. (c) EDX analysis results of the amorphous composite. (d−i) STEM image and the corresponding elemental mapping of Mo (purple), S (blue), O (yellow), C (red), and N (green) in the amorphous composite.

were showed in Figure 4c, indicating the presence of Mo, S, O, C, and N elements in the products, in agreement with the element content analysis (CNOSH) and ICP-OES results. Additionally, the HRTEM image of a-MM/NCc was showed in Figure 4d. To further determine the space distribution of compositional elements in a-MM/NCc, EDX element mapping was carried out. The corresponding elemental mapping of Mo, S, O, C, and N elements are displayed in Figure 4d−i, respectively, indicating the uniform distribution of the elements. Electrochemical Performance. In this work, the fundamental electrochemical properties of the amorphous composite anode materials were investigated in both LI and SI half-cell batteries. The cyclic voltammetry (CV) curves of the electrode for LIBs are first shown in Figure 5. The CV measurement is demonstrated in the voltage range of 0.01−3.0 V at a scan rate of 0.05 mV s−1 and the lithium plate was acted as counter electrode. The CV shape of a-MM/NCc electrode was significantly different from the pure electrode of MoS2 or MoO3. As shown in Figure 5, there was a clear cathodic peak at around 1.875 V in the first discharge cycle, corresponding to the intercalation of Li+ into the interlayer spacing between the Mo−O octahedron layer and Mo−O octahedron interlayer of the amorphous composite to form LixMoO3, which is related to the reaction of MoO3 + xLi+ + xe− → LixMoO3 (I).48,49 The weak cathodic peak at around 1.0 V subsequently was corresponding to insertion of Li+ ions into the interlayer

Figure 5. Cyclic voltammetry curves of the electrode of the amorphous composite for LIBs case at a scan rate of 0.05 mV s−1 from 0 to 3.0 V.

spacing between the Mo−S layer of the amorphous composite to form LixMoS2, which is assigned to the reaction of MoS2 + xLi+ + xe− → LixMoS2 (II).50,51 The broad weak cathodic peak below 0.5 V is associated with the reaction of LixMoO3 and LixMoS2 decompositions respectively, namely, LixMoO3 + (6 − x)Li+ + (6 − x)e− → Mo + 3Li2O (III) and LixMoS2 + (4 − x)Li+ + (4 − x)e− → Mo + 2Li2S (IV).41−44 It is necessary to 8028


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Figure 6. Electrochemical performance of the electrode of the amorphous composite for LIB case. (a) Cyclic performances of the amorphous composite electrode at 100 mA g−1. (b) The charge/discharge voltage-specific capacity curves of the first, third, fifth, 10th, 20th, and 50th cycles. (c) Rate performances of the amorphous composite electrode from 50 to 2000 mA g−1. (d) Cycling performance of the electrode at a high current density 1000 mA g−1.

specific capacity of a-MM/NCc was as high as 1816.1 mA h g−1, significantly exceeding the theoretical specific capacity of MoO3 and MoS2 electrodes (1111 and 670 mA h g−1, respectively.), which may be owed to this unique structure and compositional features within the amorphous composite providing massive insertion sites for lithium ions. Relatively, it delivered a charge specific capacity of 1369.3 mA h g−1. It should be noted that the irreversible specific capacity mainly results from the formation of the SEI layer, corresponding to an initial Coulombic efficiency of 75.4%. In the next two charge/discharge cycles, the discharge specific capacity gradually tended to be stable with a slight decline, and it can be intuitively observed that the discharge specific capacity of a-MM/NCc almost showed no decline from a fourth cycle to a 50th cycle. Improbably, the remaining discharge specific capacity of 50th cycle of a-MM/ NCc electrode reaches up to 1253.3 mA h g−1, nearly 3.7 times more than the theoretical specific capacity of current commercial graphite electrode (372 mA h g−1). The Coulombic efficiency from the fourth cycle to the 50th cycle is nearly 100% with excellent cycling stability. Meanwhile, the voltage-specific

point out that the cathodic peak at 0.1 V is corresponding to the inevitable formation of a solid−electrolyte interface (SEI) layer on the surface of the amorphous composite electrode, which disappeared in the following two cycles. During the first charge process, there are two obvious anodic plateaus at 1.47 and 2.35 V which can be ascribed to the reversible reactions of I and II, respectively. Similarly, the broad weak anodic peaks between 0 and 1.0 V can be attributed to the reversible reactions of III and IV.41−45 In the following two CV loops, it can be clearly observed the CV curves perfectly overlap together, suggesting that a-MM/NCc electrode reveals a significant capability and superior cycling stability. Thus, it can be concluded that the mechanism of lithium storage in aMM/NCc electrode is that the Li+ insertion/extraction into/ from the interlayer spacing between the Mo−O layer and Mo− S layer, respectively. The electrochemical cycling performance of a-MM/NCc electrode as LIBs anode material at a current density of 100 mA g−1 in the voltage range of 0.01−3.0 V vs Li/Li + was presented at the Figure 6a. In the first electrochemical cycle, the discharge 8029


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electrolyte and avoid the exfoliation of the active material from copper foil in the electrolyte during the entire charge− discharge cycling test. Correspondingly, the next charge semicircle is corresponding to the sodium ions extraction from a-MM/NCc electrode. The broad weak anodic peak around 0.45 V was due to the Na+ extraction from the sodium oxide or sodium sulfide to form the NaxMoO3 or NaxMoS2, that is, the inverse reaction of VII and VIII occurred, respectively. Meanwhile, the anodic peaks at 1.41 and 1.65 V were assigned to the reversible reactions of V and VI during the first charge semicircle.45−48 Similarly, corresponding to the above LIBs CV curves, the SIBs CV curves of the following cycles can overlap together perfectly, indicating superior stable cycling performance of the active material. Hence, it can be concluded that the mechanism of the a-MM/NCc electrode for SIBs is the Na+ insertion/extraction into/from the interlayer spacing between the Mo−O layer and Mo−S layer, respectively, which is similar to that of LIBs. Also, the electrochemical characteristics of the amorphous composite electrode for SIBs were examined by the constant current charge−discharge circling method in the voltage range of 0.01−3.0 V vs Na/Na+. As described in the Figure 8a, the discharge specific capacity of a-MM/NCc electrode at a current density of 300 mA g−1 was up to 827.9 mA h g−1 in the first discharge process. That is to say, this unique structure and compositional features in the amorphous active material can provide enough space for the insertion/extraction of not only lithium ions but also sodium ions. As such, the subsequent charge specific capacity of the active material can still reach to 553.4 mA h g−1, displaying the initial Coulombic efficiency of 66.8%, in spite of the irreversible reaction to the formation of the SEI film. Meanwhile, it can be observed that the trend of the discharge specific capacity curve in the early 40 cycles slightly decreases and then increases gradually to be steady. Significantly, after 200 charge/discharge cycles, the discharge specific capacity of a-MM/NCc electrode for SIBs can reach 538.7 mA h g−1 with a capacity retention of 97% except for the first cycle, indicating that the active material has excellent cycle stability. As shown in Figure 8b, the voltage-specific capacity curve of the a-MM/NCc electrode clearly demonstrates two pairs of stable charge and discharge platforms, namely 0.45/ 1.25 and1.41/2.10 V, which are consistent with the CV curves. At this point, it can be concluded that the active material has superior electrochemical performance by observing the charge/ discharge voltage-specific capacity curves of the third, 10th, 50th, 100th, and 200th cycles which almost overlap together. The result of rate capacity test to a-MM/NCc electrode for SIBs at different current densities was shown in Figure 8c. From the curves of rate performance it can be seen that a-MM/ NCc electrode exhibits high rate stability. To be specific, when tested at the initial low current density of 50 mA g−1, the discharge specific capacity of the active material can amazingly reach 907.4 mA h g−1 in the first cycle and around 655.9 mA h g−1 in the next nine cycles with a Coulombic efficiency of 72.2%. Beyond that, an ideal discharge specific capacity of 310.1 mA h g−1 was still retained when the current density was up to 1000 mA g−1. Additionally, the discharge specific capacity was well-recovered when the current density returned to100 mA g−1 after the high current density of 1000 mAg−1, which suggests that a-MM/NCc electrode has superior rate capacity. Figure 8d shows that a-MM/NCc electrode has superior performance of long-term cycling stability at a large current density of 1000 mA g−1. The discharge specific capacity of a-MM/NCc electrode for

capacity of a-MM/NCc electrode was shown in Figure 6b. Two pairs of charge/discharge platforms were obviously observed in the curve, namely 2.35/1.875 and 1.47/0.5 V, which is supported by the CV curves. Apparently the charge/discharge voltage-specific capacity curves of the third, fifth, 10th, 20th, and 50th cycles almost overlap together, also indicating that aMM/NCc electrode delivers excellent cycling stability. In order to further detect the electrochemical performance of a-MM/NCc electrode, rate capacity is also tested at different current densities, namely, 50, 100, 200, 300, 500, 1000, and 2000 mA g−1. Quite evidently, the results of the rate capacity test were exhibited in Figure 6c, revealing excellent rate capability and stable cycling performance, too. More specifically, the discharge specific capacity of a-MM/NCc electrode at a large current density of 2000 mA g−1 can still reach at 497.6 mA h g−1, and the discharge specific capacity of a-MM/NCc electrode has no obvious decline at each circulation of the rate capacity test. More delightfully, the a-MM/NCc electrode exhibits an exceptionally long-term cycling stability of LIBs. As can be seen from Figure 6d, the electrode achieves a marked high stable specific capacity of 887.5 mA h g−1 at a current density of 1000 mA g−1 after 350 cycles. Noticeably, the Coulombic efficiency of a-MM/NCc electrode are nearly 100% during the entire long-term cycling test except for the initial several cycles, which has not been previously reported as far as we know. Similarly, the electrochemical properties of a-MM/NCc electrode used as SIBs anode material were also explored. Figure 7 shows the CV curve of a-MM/NCc electrode for SIBs

Figure 7. Cyclic voltammetry curves of the electrode of the amorphous composite for the SIB case at a scan rate of 0.05 mV s−1 from 0 to 3.0 V.

where the counter electrode was acted by the sodium tablets with a voltage range of 0.01−3.0 V at a scan rate of 0.05 mV s−1. The first cathodic peak observed in the initial discharge semicircle was located at around 2.10 V, which corresponds to the reaction of MoO3 + xNa+ + xe− → NaxMoO3 (V).52,53 The next cathodic plateau at around 1.25 V is according to the reaction of MoS2 + xNa+ + xe− → NaxMoS2 (VI).54,55 With the further intercalation of the sodium ions into the active material, the subsequent reactions below 1.0 V are NaxMoO3 + (6 − x)Na+ + (6 − x)e− → Mo + 3Na2O (VII) and NaxMoS2 + (4 − x)e− → Mo + 2Na2S (VIII).45−48 Moreover, it must be noted that the cathodic reaction at 0.1 V is to form the compact SEI films, which could inhibit further decomposition of 8030


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Figure 8. Electrochemical performance of the electrode of the amorphous composite for SIBs case. (a) Cyclic performances of the amorphous composite electrode at 300 mA g−1. (b) The charge/discharge voltage-specific capacity curves of the first, third, fifth, 10th, 20th, and 50th cycles. (c) Rate performances of the amorphous composite electrode from 50 to 1000 mA g−1. (d) Cycling performance of the electrode at a high current density 1000 mA g−1.

Table 2. Performance Comparison for Molybdenum-Based Materials with Crystal Structure for LIBs with Crystal Structure materials Present work MoO2/ GO18 MoO3/ GO19 MoO3@ C58 MoS2/ CMK-350 TiO2/ MoS255 MoS2/ GO59 MoSe2@ PHCS21 MoSe2/C60

specific capacity at lower current density mA h g−1 (A g−1)

specific capacity at higher current density mA h g−1 (A g−1)

capacity retention after certain cycles % (cycle)

coulombic efficiency at first cycle %

amorphous or crystal phase

1253.3 (0.1)

887.5 (1)

nearly 100% (350)

75.4

amorphous

79.4% (40)

63.7

crystal

963.4 (0.06) 953 (0.2)

754.6 (1)

83.3% (200)

72.1

crystal

696 (0.2)

502 (1)

79.9% (100)

66.6

crystal

893 (0.1)

391 (8)

97.4% (150)

69

crystal

421 (0.1)

112 (20)

83.1% (100)

71.6

crystal

890 (0.1)

545 (2)

71% (100)

76

crystal

820 (0.5)

640 (3)

98% (100)

57.4

crystal

650 (0.1)

450 (2)

93% (50)

72.2

crystal

SIBs can reach 339.9 mA h g−1 after 220 cycles, nearly 100% retention of its initial discharge specific capacity except for the

first cycle, which indicates that the active material exhibits excellent cycling stability. 8031


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Table 3. Performance Comparison for Molybdenum-Based Materials with Crystal Structure for SIBs with Crystal Structure materials

specific capacity at lower current density mA h g−1 (A g−1)

Specific capacity at higher current density mA h g−1 (A g−1)

capacity retention after certain cycles % (cycle)

coulombic efficiency at first cycle %

amorphous or crystal phase

present work α-MoO353 MoO3/GO52 TiO2/MoS255 MoS2/RGO22 MoS2/C61 MoSe2@PHCS21 MoSe262

655.9 (0.05) 213 (0.1117) 875 (0.058) 214 (0.02) 450 (0.1) 610 (0.05) 575 (0.2) 442 (0.1)

310.1 (1) 100 (1.117) 330 (1.117) 48 (4) 300 (2) 370 (2.5) 400 (1.5) 315 (1.5)

97% (220) 55% (500) 71% (100) 82.3% (100) 81.1% (160) 80% (200) 90% (100) 96% (50)

66.8 53.2 88 62.2 64 80 65.9 85

amorphous crystal crystal crystal crystal crystal crystal crystal

Compared with recently reported molybdenum-based materials with crystal structure for both LIBs and SIBs, it can be clearly seen that the a-MM/NCc in our work shows much better electrochemical performance, as listed in Tables 2 and 3. The excellent electrochemical performance of a-MM/NCc may be resulted from a series of aspects as follows: (1) The carbonaceous matrix can enhance the conductivity of the amorphous composite. (2) Heteroatom, such as N, doping within this unique compositional features can increase the active ions absorption sites on the amorphous composite surface which benefitted the insertion/extraction of lithium/ sodium ions. (3) The hybrid nanomaterials could provide plenty of diffusion channels for ions during the insertion/ extraction process.56,57 (4) 1D chain structure reduces the transfer distance of lithium/sodium ions into/from the electrode.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.7b01595. XRD patterns and SEM images of the Mo3O10(C2H10N2) nanowire and Raman spectra of the as-prepared amorphous composite (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (X.W.). *E-mail: [email protected] (J.L.). ORCID

Jun Liu: 0000-0003-0048-0115 Linyu Yang: 0000-0003-0246-2754 Notes

The authors declare no competing financial interest.

CONCLUSIONS

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In summary, a novel amorphous MoS2/MoO3/nitrogen-doped carbon composite (a-MM/NCc) has been synthesized for the first time. The synthesis strategy only involves partially sulfurizing organic−inorganic hybrid material Mo 3 O 10 (C2H10N2) nanowire precursors under low temperature (300 °C). More interestingly, a-MM/NCc electrodes show excellent electrochemical performance for LIBs and SIBs. For instance, aMM/NCc electrode for LIBs can reach up to 1253.3 mA h g−1 at a current density of 100 mA g−1 after 50 cycles. Similarly, for SIBs, it also retains 538.7 mA h g−1 after 200 cycles at 300 mA g−1. The a-MM/NCc electrode has superior performance of long-term cycling stability at a large current density of 1000 mA g−1 both for LIBs and SIBs, which both capacity retentions of their corresponding initial discharge specific capacity are near up to 100%. Such superior performance may be attributed to nitrogen and carbon codoping within this unique amorphous composite which not only enhances the conductivity but also increases the active ions absorption sites on the amorphous composite surface. Besides, the hybrid nanomaterials could provide plenty of diffusion channels for ions during the insertion/extraction process. And 1D chain structure reduces the transfer distance of lithium/sodium ions into/from the electrode. As far as we know, such a novel amorphous composite has much better electrochemical performance than that of most previously reported molybdenum-based materials with crystal structure. Therefore, our work may shed some light on the exploration of the next generation energy transfer and storage devices.

ACKNOWLEDGMENTS This work is supported by the National Natural Science Foundation of China (grant Nos. 51472271, 61376018, and 51174233), the Project of Innovation-driven Plan in Central South University (2016CX002), and the National Basic Research Program of China (973 Program) grant No. 2013CB932901.

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REFERENCES

(1) Dunn, B.; Tarascon, J. M.; Kamath, H. Electrical energy storage for the grid: a battery of choices. Science 2011, 334 (6058), 928−935. (2) Lu, L.; Han, X.; Li, J.; Hua, J.; Ouyang, M. A review on the key issues for lithium-ion battery management in electric vehicles. J. Power Sources 2013, 226 (3), 272−288. (3) Liu, J.; Lu, P. J.; Liang, S.; Liu, J.; Wang, W.; Lei, M.; Tang, S.; Yang, Q. Ultrathin Li3VO4 nanoribbon/graphene sandwich-like nanostructures with ultrahigh lithium ion storage properties. Nano Energy 2015, 12, 709−724. (4) Winter, M.; Besenhard, J. O.; Spahr, M. E.; Novák, P. Insertion Electrode Materials for Rechargeable Lithium Batteries. Adv. Mater. 1998, 10 (10), 725−763. (5) Etacheri, V.; Marom, R.; Elazari, R.; Salitra, G.; Aurbach, D. Challenges in the Development of Advanced Li-Ion Batteries: A Review. Energy Environ. Sci. 2011, 4 (9), 3243−3262. (6) Goodenough, J. B.; Park, K. S. The Li-ion rechargeable battery: a perspective. J. Am. Chem. Soc. 2013, 135 (4), 1167−1176. (7) Li, H. Z.; Yang, L. Y.; Liu, J.; Li, S. T.; Fang, L. B.; Lu, Y. K.; Yang, H. R.; Liu, S. L.; Lei, M. Improved electrochemical performance of yolk-shell structured SnO2@void@C porous nanowires as anode for lithium and sodium batteries. J. Power Sources 2016, 324, 780−787. (8) Wu, C.; Maier, J.; Yu, Y. Generalizable Synthesis of MetalSulfides/Carbon Hybrids with Multiscale, Hierarchically Ordered 8032


Research Article

ACS Sustainable Chemistry & Engineering Structures as Advanced Electrodes for Lithium Storage. Adv. Mater. 2016, 28 (1), 174−180. (9) Zhang, K.; Park, M.; Zhou, L.; Lee, G. H.; Li, W.; Kang, Y. M.; Chen, J. Urchin-like CoSe2 as a high-performance anode material for sodium-ion batteries. Adv. Funct. Mater. 2016, 26 (37), 6728−6735. (10) Zhu, K. J.; Liu, G.; Wang, Y. J.; Liu, J.; Li, S. T.; Yang, L. Y.; Liu, S. L.; Wang, H.; Xie, T. Metal-Organic Frameworks derived novel hierarchical durian-like nickel sulfide (NiS2) as an anode material for high-performance sodium-ion batteries. Mater. Lett. 2017, 197, 180− 183. (11) Zhuo, L.; Wu, Y.; Wang, L.; Yu, Y.; Zhang, X.; Zhao, F. Onestep hydrothermal synthesis of SnS2/graphene composites as anode material for highly efficient rechargeable lithium ion batteries. RSC Adv. 2012, 2 (12), 5084−5087. (12) Zou, Y.; Chen, S.; Yang, X.; Ma, N.; Xia, Y.; Yang, D.; Guo, S. Li-ion batteries: suppressing Fe-Li antisite defects in LiFePO4/Carbon hybrid microtube to enhance the lithium ion storage. Adv. Energy Mater. 2016, 6, 1670139. (13) Yang, L. Y.; Li, H. Z.; Liu, J.; Sun, Z. Q.; Tang, S. S.; Lei, M. Dual yolk-shell structure of carbon and silica-coated silicon for highperformance lithium-ion batteries. Sci. Rep. 2015, 5, 10908. (14) Pan, H.; Hu, Y. S.; Chen, L. Room-temperature stationary sodium-ion batteries for large-scale electric energy storage. Energy Environ. Sci. 2013, 6 (8), 2338−2360. (15) Peters, J. F.; Buchholz, D.; Passerini, S.; Weil, M. Life cycle assessment of sodium-ion batteries. Energy Environ. Sci. 2016, 9 (5), 1744−1751. (16) Zhu, K. J.; Liu, J.; Li, S. T.; Liu, L. L.; Yang, L. Y.; Liu, S. L.; Wang, H.; Xie, T. Ultrafine Cobalt Phosphide nanoparticles embedded in nitrogen-doped carbon matrix as a superior anode material for lithium ion batteries. Adv. Mater. Interfaces 2017, 1700377. (17) Liu, S. L.; Huang, J.; Liu, J.; Lei, M.; Min, J.; Li, S.; Liu, G. Porous Mo2N nanobelts as a new anode material for sodium-ion batteries. Mater. Lett. 2016, 172, 56−59. (18) Yang, Q.; Liang, Q.; Liu, J.; Liang, S.; Tang, S.; Lu, P.; Lu, Y. Ultrafine MoO2 nanoparticles grown on graphene sheets as anode materials for lithium-ion batteries. Mater. Lett. 2014, 127 (27), 32−35. (19) Lu, P. J.; Lei, M.; Liu, J. Graphene nanosheets encapsulated αMoO3 nanoribbons with ultrahigh lithium ion storage properties. CrystEngComm 2014, 16 (29), 6745−6755. (20) Xu, X.; Fan, Z.; Ding, S.; Yu, D.; Du, Y. Fabrication of MoS2 nanosheet@TiO2 nanotube hybrid nanostructures for lithium storage. Nanoscale 2014, 6 (10), 5245−5250. (21) Yang, X.; Zhang, Z.; Fu, Y.; Li, Q. Porous hollow carbon spheres decorated with molybdenum diselenide nanosheets as anodes for highly reversible lithium and sodium storage. Nanoscale 2015, 7 (22), 10198−10203. (22) Che, Z.; Li, Y.; Chen, K.; Wei, M. Hierarchical MoS2@RGO nanosheets for high performance sodium storage. J. Power Sources 2016, 331, 50−57. (23) Zhuo, S. Z.; Xu, Y.; Zhao, W.; Zhang, J.; Zhang, P. B. Hierarchical nanosheet-based MoS2 nanotubes fabricated by an anionexchange reaction of MoO3-amine hybrid nanowires. Angew. Chem., Int. Ed. 2013, 52 (33), 8602−8606. (24) Gao, Q.; Wang, S.; Fang, H.; Weng, J.; Zhang, Y.; Mao, J.; Tang, Y. One-dimensional growth of MoOx-based organic-inorganic hybrid nanowires with tunable photochromic properties. J. Mater. Chem. 2012, 22 (11), 4709−4715. (25) Baltrusaitis, J.; Mendoza-Sanchez, B.; Fernandez, V.; Veenstra, R.; Dukstiene, N.; Roberts, A.; Fairley, N. Generalized molybdenum oxide surface chemical state XPS determination via informed amorphous sample model. Appl. Surf. Sci. 2015, 326, 151−161. (26) Peng, Y.; Meng, Z.; Zhong, C.; Lu, J.; Yang, Z.; Qian, Y. Tubeand ball-like amorphous MoS2 prepared by a solvothermal method. Mater. Chem. Phys. 2002, 73 (2), 327−329. (27) Peng, Y.; Meng, Z.; Zhong, C.; Lu, J.; Yu, W.; Yang, Z.; Qian, Y. Hydrothermal synthesis of MoS2 and its pressure-related crystallization. J. Solid State Chem. 2001, 159 (1), 170−173.

(28) Miki, Y.; Nakazato, D.; Ikuta, H.; Uchida, T.; Wakihara, M. Amorphous MoS2 as the cathode of lithium secondary batteries. J. Power Sources 1995, 54 (2), 508−510. (29) Cho, B.; Kim, A. R.; Park, Y.; Yoon, J.; Lee, Y. J.; Lee, S.; Yoo, T. J.; Kang, C. G.; Lee, B. H.; Ko, H. C.; et al. Bifunctional sensing characteristics of chemical vapor deposition synthesized atomic-layered MoS2. ACS Appl. Mater. Interfaces 2015, 7 (4), 2952−2959. (30) Wang, D. Z.; Xiao, Y. Y.; Luo, X. N.; Wu, Z. Z.; Wang, Y. J.; Fang, B. Z. Swollen ammoniated MoS2 with 1T/2H hybrid phases for high-rate electrochemical energy storage. ACS Sustainable Chem. Eng. 2017, 5, 2509−2515. (31) Torres, J.; Alfonso, J. E.; López-Carreño, L. D. XPS and X-ray diffraction characterization of MoO3 thin films prepared by laser evaporation. Phys. Status Solidi C 2005, 2 (10), 3726−3729. ́ (32) Swiatowskamrowiecka, J.; de Diesbach, S. D.; Maurice, V.; Zanna, S.; Klein, L.; Briand, E.; Vickridge, I.; Marcus, P. Li-ion intercalation in thermal oxide thin films of MoO3 as studied by XPS, RBS, and NRA. J. Phys. Chem. C 2008, 112 (29), 11050−11058. (33) Scanlon, D. O.; Watson, G. W.; Payne, D. J.; Atkinson, G. R.; Egdell, R. G.; Law, D. S. L. Theoretical and experimental study of the electronic structures of MoO3 and MoO2. J. Phys. Chem. C 2010, 114 (10), 4636−4645. (34) Liu, Q. C.; Xu, J. J.; Yuan, S.; Chang, Z. W.; Xu, D.; Yin, Y. B.; Li, L.; Zhong, H. X.; Jiang, Y. S.; Yan, J. M.; Zhang, X.-B. Artificial protection film on lithium metal anode toward long-cycle-life lithiumoxygen batteries. Adv. Mater. 2015, 27, 5241−5247. (35) Liu, J.; Tang, S.; Lu, Y.; Cai, G.; Liang, S.; Wang, W.; Chen, X. Synthesis of Mo2N nanolayer coated MoO2 hollow nanostructures as high-performance anode materials for lithium-ion batteries. Energy Environ. Sci. 2013, 6 (9), 2691−2697. (36) Wang, F.; Song, S.; Li, K.; Li, J.; Pan, J.; Yao, S.; Ge, X.; Feng, J.; Wang, X.; Zhang, H. A "Solid Dual-Ions-Transformation" Route to S,N Co-doped carbon nanotubes as highly efficient "metal-free" catalysts for organic reactions. Adv. Mater. 2016, 28, 10679−10683. (37) Chen, Z.; Cummins, D.; Reinecke, B. N.; Clark, E.; Sunkara, M. K.; Jaramillo, T. F. Core-shell MoO3-MoS2 nanowires for hydrogen evolution: a functional design for electrocatalytic materials. Nano Lett. 2011, 11 (10), 4168−4175. (38) Pacley, S.; Hu, J.; Jespersen, M.; Hilton, A.; Waite, A.; Brausch, J.; Beckmillerton, E.; Voevodin, A. A. Impact of reduced graphene oxide on MoS2 grown by sulfurization of sputtered MoO3 and Mo precursor films. J. Vac. Sci. Technol., A 2016, 34 (4), 041505. (39) Silipigni, L.; Barreca, F.; Fazio, E.; Neri, F.; Spanò, T.; Piazza, S.; Sunseri, C.; Inguanta, R. Template electrochemical growth and properties of Mo oxide nanostructures. J. Phys. Chem. C 2014, 118 (38), 22299−22308. (40) Wang, X.; Hong, M. Z.; Zhang, F. W.; Zhuang, Z. Y.; Yu, Y. Recyclable nanoscale zero valent iron doped g-C3N4/MoS2 for efficient photocatalysis of RhB and Cr(VI) driven by visible light. ACS Sustainable Chem. Eng. 2016, 4, 4055−4063. (41) Wang, Y.; Cong, C.; Qiu, C.; Yu, T. Raman spectroscopy study of lattice vibration and crystallographic orientation of monolayer MoS2 under uniaxial strain. Small 2013, 9 (17), 2857−2861. (42) Brennan, C. J.; Nguyen, J.; Yu, E. T.; Lu, N. Interface adhesion between 2D materials and elastomers measured by buckle delaminations. Adv. Mater. Interfaces 2015, 2 (16), 1500176. (43) Windom, B. C.; Sawyer, W. G.; Hahn, D. W. A Raman spectroscopic study of MoS2 and MoO3: applications to tribological systems. Tribol. Lett. 2011, 42 (3), 301−310. (44) Xie, W.; Su, M.; Zheng, Z.; Wang, Y.; Gong, L.; Xie, F.; Zhang, W.; Zhi, L.; Luo, J.; Liu, P.; et al. Nanoscale insights into the hydrogenation process of layered α-MoO3. ACS Nano 2016, 10 (1), 1662−1670. (45) Ferrari, A. C.; Robertson, J. Raman spectroscopy of amorphous, nanostructured, diamond-like carbon, and nanodiamond. Philos. Trans. R. Soc., A 2004, 362 (1824), 2477−2512. (46) Wu, J.; Liu, M.; Chatterjee, K.; Hackenberg, K. P.; Shen, J.; Zou, X.; Yan, Y.; Gu, J.; Yang, Y.; Lou, J.; Ajayan, P. M. Exfoliated 2D transition metal disulfides for enhanced electrocatalysis of oxygen 8033


Research Article

ACS Sustainable Chemistry & Engineering evolution reaction in acidic medium. Adv. Mater. Interfaces 2016, 3, 1500669. (47) Ren, D.; Hu, Y.; Jiang, H.; Deng, Z.; Petr, S.; Jiang, H.; Li, C. Salt-templating protocol to realize few-layered ultrasmall MoS2 nanosheets inlayed into carbon frameworks for superior lithium-ion batteries. ACS Sustainable Chem. Eng. 2016, 4 (3), 1148−1153. (48) Yu, X.; Wang, L.; Liu, J.; Sun, X. Porous MoO3 film as a high performance anode material for lithium-ion batteries. ChemElectroChem 2014, 1 (9), 1476−1479. (49) Wang, C.; Wu, L.; Wang, H.; Zuo, W.; Li, Y.; Liu, J. Fabrication and shell optimization of synergistic TiO2-MoO3 core-shell nanowire array anode for high energy and power density lithium-ion batteries. Adv. Funct. Mater. 2015, 25 (23), 3524−3533. (50) Xu, X.; Fan, Z.; Yu, X.; Ding, S.; Yu, D.; Lou, X. W. A nanosheets-on-channel architecture constructed from MoS2 and CMK-3 for high-capacity and long-cycle-life lithium storage. Adv. Energy Mater. 2014, 4 (17), 1400902. (51) 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 (25), 7395−7398. (52) Sreedhara, M. B.; Santhosha, A. L.; Bhattacharyya, A. J.; Rao, C. N. R. Composite of few-layer MoO3 nanosheets with graphene as a high performance anode for sodium-ion batteries. J. Mater. Chem. A 2016, 4 (24), 9466−9471. (53) Hariharan, S.; Saravanan, K.; Balaya, P. α-MoO3: A high performance anode material for sodium-ion batteries. Electrochem. Commun. 2013, 31, 5−9. (54) 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 (9), 1501937. (55) Liao, J. Y.; Luna, B. D.; Manthiram, A. TiO2-B nanowire arrays coated with layered MoS2 nanosheets for lithium and sodium storage. J. Mater. Chem. A 2016, 4 (3), 801−806. (56) Liu, H.; Chen, X.; Deng, L.; Ding, M.; Li, J.; He, X. Perpendicular growth of few-layered MoS2 nanosheets on MoO3 nanowires fabricated by direct anion exchange reactions for highperformance lithium-ion batteries. J. Mater. Chem. A 2016, 4 (45), 17764−17772. (57) Villevieille, C.; Wang, X. J.; Krumeich, F.; Nesper, R.; Novák, P. MoS2 coating on MoO3 nanobelts: A novel approach for a high specific charge electrode for rechargeable Li-ion batteries. J. Power Sources 2015, 279, 636−644. (58) Li, X.; Xu, J.; Mei, L.; Zhang, Z.; Cui, C.; Liu, H.; Ma, J.; Dou, S. Electrospinning of crystalline MoO3@C nanofibers for high-rate lithium storage. J. Mater. Chem. A 2015, 3 (7), 3257−3260. (59) Liu, Y. T.; Zhu, X. D.; Duan, Z. Q.; Xie, X. M. Flexible and robust MoS2-graphene hybrid paper cross-linked by a polymer ligand: a high-performance anode material for thin film lithium-ion batteries. Chem. Commun. 2013, 49 (87), 10305−10307. (60) Liu, Y.; Zhu, M. Q.; Chen, D. Sheet-like MoSe2/C composites with enhanced Li-ion storage properties. J. Mater. Chem. A 2015, 3 (22), 11857−11862. (61) Zhang, X.; Li, X.; Liang, J.; Zhu, Y.; Qian, Y. Synthesis of MoS2@C nanotubes via the kirkendall effect with enhanced electrochemical performance for lithium ion and sodium ion batteries. Small 2016, 12 (18), 2484−2491. (62) Ko, Y. N.; Choi, S. H.; Park, S. B.; Kang, Y. C. Hierarchical MoSe2 yolk-shell microspheres with superior Na-ion storage properties. Nanoscale 2014, 6 (18), 10511−10515.

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