Highly Crystalized Co2Mo3O8 Hexagonal Nanoplates Interconnected

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Energy, Environmental, and Catalysis Applications

Highly Crystalized Co2Mo3O8 Hexagonal Nanoplates Interconnected by Coal Derived Carbon via the MoltenSalt-Assisted Method for Competitive Li-Ion Battery Anode Shasha Gao, Yakun Tang, Yang Gao, Lang Liu, Hongyang Zhao, Xiaohui Li, and Xuzhen Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b20366 • Publication Date (Web): 28 Jan 2019 Downloaded from http://pubs.acs.org on January 29, 2019

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ACS Applied Materials & Interfaces

Highly

Crystalized

Co2Mo3O8

Hexagonal

Nanoplates Interconnected by Coal Derived Carbon via

the

Molten-Salt-Assisted

Method

for

Competitive Li-Ion Battery Anode Shasha Gao,† Yakun Tang,† Yang Gao† Lang Liu,*,† Hongyang Zhao,† Xiaohui Li† and Xuzhen Wang‡ †

Key Laboratory of Energy Materials Chemistry, Ministry of Education, Institute of Applied

Chemistry, Xinjiang University, Urumqi 830046, Xinjiang, China ‡

State Key Lab of Fine Chemicals, School of Chemical Engineering, Dalian University of

Technology, Dalian 116023, China KEYWORDS: Co2Mo3O8, Coal, Molten salts, Anodes, Li-ion batteries

ABSTRACT: Highly crystalized Co2Mo3O8 hexagonal nanoplates interconnected by coal derived carbon have been successfully fabricated by molten-salt-assisted method. The formation process of the nanostructural hybrids via molten salts is proposed. The eutectic salts with low melting points act as ionic liquid solvent and “molecular templates” at high temperature, making cobalt and molybdenum salts react in the form of bare ions to get the regular Co2Mo3O8 hexagonal nanoplates interconnected by conductive carbon. And the crystallinity of Co2Mo3O8

ACS Paragon Plus Environment

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hexagonal nanoplates is increased with the help of molten salts. The effects of temperature on morphology and electrochemical performance of the composites were studied. Thanks to the unique structure design, the optimal composite obtained by this simple low cost strategy exhibits remarkable electrochemical performance as anodes for LIBs, which reveals a high reversible capacity of 1075 mAh g-1 at 200 mA g-1 and 596 mAh g-1 at 1000 mA g-1 after 100 cycles. More importantly, the sample shows good rate capability with high capacity of 533 mAh g-1 at high current density of 4000 mA g-1. The molten-salt-assisted method is also applicable to design and synthesize other metal oxide-based Li-ion battery anodes.

INTRODUCTION In recent decades, the development of lithium-ion batteries (LIBs) has promoted the revolution of personal electronic devices, and has also changed our daily work and life.1-4 In order to meet the increasing energy storage requirements in the fields of portable electronic devices and electric vehicles, LIBs need to be promoted in terms of energy and power density, endurance, and safety. Therefore, exploiting anode materials for LIBs with large capacity, high rate performance and excellent cycle durability is a hot topic in recent years.5-9 Compared to commercial graphite anodes, transition metal oxides (TMOs) have a much higher capacity for lithium storage and a potential platform that is expected to be used to build LIBs with higher capacity and rate performance.10-18 Among which, molybdenum oxysalts are promising candidates for the new generation of anodes because of their higher conductivity, multiple oxidation state and higher specific capacity.19-23 However, unlike the insertion/extraction mechanism for graphite electrodes, molybdenum oxysalts usually store lithium ions through a conversion mechanism. The process is accompanied by a huge volume expansion and a sluggish


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kinetic, which easily leads to rapid attenuation of the capacity, limiting their practical applications. To solve the above problems, rationally design and regulation of the structure of molybdenum oxysalts are considered as one of most effective strategies.24-28 Chen et al prepared hollow porous CoMoO4/Co3O4 octahedrons to accelerate the permeation of the electrolyte and the transport of Li+, which possessed a capacity of 1175.1 mAh g-1 after 100 cycles at 200 mA g1 24

.

Based on the above researches, controlling the size and morphology of the materials can

improve their capacity and cycle performance. More recently, nanostructural hybrids combined with carbon have become another promising approach.29-31 For example, in order to promote the poor cycling stability and inferior rate capability of NiMoO4-based electrodes, Wang et al prepared hierarchical NiMoO4 nanowire arrays grown on graphene foam, which demonstrated a high lithium-storage capacity and excellent cycle performance (200 mA g-1, 150th cycles, 867.86 mAh g-1).29 Tian et al fabricated porous NiMoO4 decorated on carbon nanofiber, which exhibited a high reversible capacity of 1132.1 mAh g-1 at 500 mA g-1.30 The above nanostructural hybrids can buffer volume changes and avoid the particle aggregation effectively. Meanwhile, the carbon with excellent electrical conductivity can expedite mass transport and maintain the integrity of electrodes, resulting in improved electrochemical performance. Since Chowdari’s group firstly prepared LiHoMo3O8 as an anode for LIBs,32 numbers of interesting studies on hexagonal Mo3-cluster compounds as anodes have been reported, such as LiYMo3O8, A2Mo3O8 (A = Fe, Co, Mn, Zn), etc.33-38 LiYMo3O8, Mn2Mo3O8 and Co2Mo3O8 were prepared by high-temperature carbothermal reduction method.33,34 In the process, MoO3, MnO2 and CoMoO4 were reduced by commercialization carbon. The synthesis of the above compounds is usually two-steps, energy and time consuming. And the electrochemical performance is unsatisfactory. It can be realized by composing with graphene to improve the


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performance of Mo3-cluster compounds. Marka et al synthesized Co2Mo3O8/rGO composite by solid reaction and thermal annealing. The composites delivered a specific capacity of 954 mAh g-1 at 60 mA g-1 after 60 cycles.35 Petnikota et al prepared few layered graphene-complex (FLG) metal oxide composites as Li-ion battery anodes. The FLG-Co2Mo3O8, FLG-Mn2Mo3O8 and FLG-Zn2Mo3O8 composites exhibited reversible capacities of 785, 495 and 630 mAh g-1 at 180 mA g-1 after 50 cycles, respectively.36 However, few reports have ever made electrode materials with high rate behavior and stable cycle performance so far. Besides, compounds combined with graphene are costly. Therefore, the preparation of Mo3-cluster compounds with high electrochemical performance by a simple method is still a great challenge. As a special “wetchemical” synthesis route, molten-salt-assisted methods have been used to produce lots of nanomaterials at relatively low temperature using inorganic salts as solvents. The molten salts not only can make the precursor react in the liquid phase, but also act as templates and porogen. Meanwhile, the resultant products can be quickly obtained after water washing away the salts. Up to now, porous carbons have been synthesized by the simple and green environmental molten-salt-assisted methods, in which specific precursors are usually involved, such as ionic liquids, glucose and organic solvents, etc.39-41. However, coal as cheap carbon source, nanostructural hybrids with superior electrochemical performances by molten-salt-assisted methods has been rarely reported. Therefore, we have adopted the simple and sustainable molten-salt-assisted pathway to synthesize nanostructural hybrids, in which Co2Mo3O8 nanoplates interconnected by coal-based carbon. As anodes for LIBs, the hybrids demonstrate extraordinary reversible capacity, as high as 1075 mAh g-1 after 100 cycles at 200 mA g-1 and 596 mAh g-1 after 100 cycles at 1000 mA g-1. More importantly, the unique nanohybrids exhibit splendid rate performance at high current


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densities. In addition, converting coal into valuable electrode materials promotes the development of coal industry. EXPERIMENTAL SECTION Preparation of the nanohybrids. Coal was pretreated as reported by our group before.42 The eutectic salt mixture of KCl/ZnCl2 (51:49, mol/mol) was used as the solvent and the pretreated coal was used as carbon precursor. In a typical synthesis, coal (100 mg), cobalt nitrate hexahydrate (174 mg), ammonium heptamolybdate (106 mg), and the eutectic salt mixture (3.8 g) with a weight ratio of reactants/solvent = 1/10, were thoroughly mixed by ball milling. Then it was calcined at 500, 600 and 700 oC in N2. After holding for 2 h at this temperature, the samples were natural cooled to room temperature and washed with hydrochloric acid and water to remove the residual salts. All the products are denoted as CMO/C-500, CMO/C-600 and CMO/C-700, respectively. With the same method, the composite obtained without KCl/ZnCl2 at 600 oC is denoted as CMO/C-600-1. And the obtained sample without coal at 600 oC is denoted as CMO-600. Materials, Characterization, Electrochemical Measurements are in the Supporting Information.

RESULTS AND DISCUSSION The synthesis of CMO/C via the molten-salt-assisted method is schematically illustrated in Figure 1. The formation of products can be described as follows: the mixture containing molten salts and coal is calcined in an inert atmosphere, upon heating to the molten point, the salts in the molten state made cobalt and molybdenum salts react with each other in the ionized species and metal oxide crystals begin to grow under the inducement of "molecular template" of molten salts.


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Meanwhile the acidified coal is also miscible in the ionic liquid solvent and carbonized, the metal oxide crystal continued to grow and was interconnected by the carbon. After cooling down and washing, the regular hexagonal nanoplates could directly obtain, which packed each other and were interconnected by coal-based carbon.

Figure 1. Synthesis procedure of CMO/C. The XRD patterns of CMO/C-500, CMO/C-600 and CMO/C-700 are present in Figure 2a. All the samples match well with the hexagonal crystal Co2Mo3O8 (JCPDS no. 34-0511), which indicates that Co2Mo3O8 can be formed at the three temperatures. At the same time, as the temperature rose, the intensity of peaks was increased, the crystallinity of Co2Mo3O8 got better. Since the carbon in the composites was amorphous, its peaks were not observed in the samples. However, carbon content in CMO/C-500, CMO/C-600 and CMO/C-700 can be evaluated by using the elemental analysis. It can be seen from Table S1, carbon of the three samples was 10.47, 6.01 and 2.65%, respectively. The above analysis indicates that molybdenum salts in the molten salt medium have been reduced by coal-based carbon, resulting in the formation of the composite Co2Mo3O8/C at these three temperatures. In order to have an insight into the action of eutectic salts and coal, XRD patterns of CMO/C-600-1 and CMO-600 are present in Figure 2b. The major peaks of CMO/C-600-1 obtained without KCl/ZnCl2 were also indexed to the hexagonal crystal Co2Mo3O8. However, these peaks are very weak due to its bad crystallization.


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Therefore, we can speculate that the molten salts provide a liquid reaction environment during the calcination, in which the reactants are easy to contact and collide for each other, thereby, the obtained product in the presence of molten salts has better crystallinity. In addition, the main characteristic diffraction peaks of the sample CMO-600 correspond to CoMoO4 (JCPDS no. 251434). The above result indicates that pure CoMoO4 was generated without coal, which is obviously different from the product (Co2Mo3O8) under the action of coal. Therefore, we can conclude that the coal act as a reduction agent during the formation of Co2Mo3O8/C, which makes CoMoO4 reduce to Co2Mo3O8 by carbothermal reduction method.34

Figure 2. XRD patterns of CMO/C-500, CMO/C-600 and CMO/C-700 (a), CMO/C-600-1 and CMO-600 (b). XPS was also carried out for study the chemical and surface states of CMO/C-600. As shown in Figure S1, the full XPS spectrum of CMO/C-600 indicates the existence of C, O, Mo and Co. The high-resolution Co 2p spectra are shown in Figure 3a, which reveals typical split spin-orbit Co 2p3/2 and Co 2p1/2 components and the corresponding satellite peaks. Meanwhile, broad and intense satellite bands indicate that only high-spin divalent cobalt (Co2+) exists at the surface of the composites.43,44 In Figure 3b, two peaks at 230.5 and 233.7 eV correspond to Mo 3d3/2 and Mo 3d5/2 states of Mo4+, the peaks at 232.2 and 235.4 eV correspond to Mo 3d5/2 and Mo 3d3/2 state of Mo6+, indicating that surface of the sample is partially oxidized to Mo6+.43,45 The spectra


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of C 1s shown in Figure 3c contain three peaks. The peak at 284.5 eV is assigned to sp2 carbon atoms, and the peaks at 286.6 and 288.7 eV can be assigned to the C-O and C=O bonds.46 As shown in Figure 3d, the peak at 530.0 eV corresponds to Co-O-Mo, and the peaks at 530.3 and 531.7 eV can be assigned to -OH and O-C=O in CMO/C-600.43 The results from XPS further prove that Co2Mo3O8 was successfully obtained by molten-salt-assisted carbothermal reduction method.

Figure 3. High-resolution XPS spectra Co 2p (a), Mo 3d (b), C 1s (c) and O 1s (d) of CMO/C600. The morphology of the samples was analyzed by SEM, TEM and HRTEM, and the results are shown in Figure 4. From Figure 4a-c, CMO/C-500, CMO/C-600 and CMO/C-700 are mainly composed of hexagon nanoplates. But, the calcination temperature has an obvious effect on the integrality of nanoplates. In Figure 4a, the sheet-like structure of the regular hexagon is not completely formed for CMO/C-500. As the temperature is raised to 600 oC, lots of regular


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hexagonal nanoplates have been completely formed and the thickness of hexagonal nanoplates is about 34 nm (Figure 4b). As can be seen from Figure S2, the energy-dispersive spectral (EDS) element mapping of CMO/C-600 displays the distribution of C, O, Co and Mo. It is clearly seen that hexagonal Co2Mo3O8 nanoplates are interconnected by the carbon. When the temperature increased to 700 oC, the hexagon nanoplates became thick. It is possible because the metal oxides crystal does not totally grow up in the low temperature (500 oC), and in the high temperature (700 oC) the crystal overgrowths, resulting in thick nanoplates. In order to discuss the function of molten salts in morphology formation, the SEM image of CMO/C-600-1 is shown in Figure 4d. It can be seen that the sample consists of particles. Hence, during the calcination process, the cobalt and molybdenum salts react with each other in the form of “bare” ions to reduce the energy barrier of the reaction due to the extremely strong polarity of molten salts in molten state. And with the help of molten salts “molecule template”, the crystal of metal oxides grow into hexagonal nanoplates. And the ionic liquid molten salts dissolve the coal, the carbonized coal acts as reducing agent and interconnects the Co2Mo3O8 hexagonal nanoplates. The morphology of the samples at different temperatures was further characterized by TEM. From the TEM images in Figure 4e-h, we can observe that the hexagonal Co2Mo3O8 nanoplates are uniformly interconnected by the carbon layer, which is consistent with the SEM results. To further investigate the internal structure of the sample CMO/C-600, HRTEM was performed, which was shown in Figure 4h. A lattice fringe with a spacing of 0.243 nm can be observed, which corresponds to the (201) plane of Co2Mo3O8. Meanwhile, it can be seen that Co2Mo3O8 is embedded in the amorphous carbon networks. These nanohybrids can effectively alleviate the volume expansion and prevent the agglomeration of Co2Mo3O8 nanoplates during Li+ insertionextraction processes.


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Figure 4. SEM and TEM images of CMO/C-500 (a, e), CMO/C-600 (b, f, h), CMO/C-700 (c, g) and CMO/C-600-1 (d). In order to further understand the structural characteristics of all the samples, N2 adsorptiondesorption isotherms and pore size distribution profiles are shown in Figure S3. The N2 adsorption-desorption isotherms of CMO/C-500, CMO/C-600, CMO/C-700 and CMO/C-600-1 have the characteristics of type IV hysteresis, a certain hysteresis loop appears at P/P0 > 0.4, indicating that the samples contain a certain amount of mesopores. The specific surface areas of CMO/C-500, CMO/C-600, CMO/C-700 and CMO/C-600-1 are 127, 267, 152 and 97 m2 g-1, respectively. Among which, CMO/C-600 possesses the biggest specific surface area due to abundant micropores (< 2 nm) and mesorpores (2-50 nm). Besides, there are some macropores (50-100 nm). Such porous materials can accelerate the permeation of electrolyte and the transport of Li+ and electrons, resulting in outstanding behaviors in LIBs application. However, the SBET of CMO/C-600-1 is 97 m2 g-1, indicating the molten salts as “molecular templates” have advantages on improving the specific surface area and porous structure of Co2Mo3O8/C. The electrochemical performances of the as-prepared CMO/C-500, CMO/C-600 and CMO/C700 in LIBs were investigated. As can be seen from Figure 5a, CMO/C-500, CMO/C-600 and CMO/C-700 show excellent cycling behaviors and high reversible capacity at 200 mA g-1. The


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reversible capacities of all the three samples are obviously increased upon cycling, their capacities are 768, 1075 and 978 mAh g-1 after 100 cycles, respectively. The explanation for such phenomena may be the porous structures of carbon can release more active sites for lithium storage, leading to the increase of the capacity. The formation of SEI layer can improve the mechanical cohesion of the active materials without hindering the ion transfer and provide extra lithium ion storage sites through the so-called “pseudo-capacitance” phenomenon. Furthermore, CMO/C-600 reveals excellent electrochemical performance in contrast, which is readily attributed to the advantageous of the integrity of double continuous phase. The structure ensured Co2Mo3O8 and carbon have good interaction. Meanwhile, the highly conductive carbon facilitates a conducting network for electrolyte to get adsorbed throughout the composite, which in turn enhances Li+ transportation in the composite. Furthermore, the rate capabilities were also evaluated at different current densities ranging from 100 to 4000 mA g-1 to test the ultrafast charging and discharging capability of the CMO/C-500, CMO/C-600 and CMO/C-700 electrodes (Figure 5b). At 100 mA g-1, the three electrodes deliver a considerably high discharge capacity of 730, 891 and 726 mAh g-1 at the 2nd cycle, respectively. Even at high current density, the three electrodes can still achieve high capacities. Meanwhile, stable capacities of the three electrodes can be obtained when the current density was reset back to an initial value of 100 mA g-1. Especially CMO/C-600, even at 4000 mA g-1, it can still achieve the high capacity of 533 mAh g-1, indicating the good reversibility and stability of the electrode at high current densities. In view of the remarkable lithium storage performance of CMO/C-600 and to elucidate the Li+ insertion-extraction processes, the CV measurements of CMO/C-600 are further carried out at a scan rate of 0.1 mV s-1 between 0.01 and 3 V, which is shown in Figure 5c. In the first cycle, there is an obvious peak in the low voltage range approaching 0 V, which is ascribed to the


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insertion and extraction of Li+ in the porous carbon.47 Besides, two peaks at 1.22, 0.63 V are seen, and a broad oxidation peak is observed at a potential of 1.50 V. The peak position and intensity in the subsequent cycles coincide well, indicating the highly reversible redox reaction of the assynthesized composite. The CV profiles remain steady after the first cycle, suggesting that the as-prepared CMO/C-600 has good stability and reversibility for the insertion and extraction of Li+. According to previous reports,34,36 the electrochemical processes of the electrodes can be described as follows: Co2Mo3O8 + 16Li+ + 16e- → 2Co0 + 3Mo0 + 8Li2O

(1)

2Co + 2Li2O → 2CoO + 4Li+ + 4e-

(2)

3Mo + 6Li2O → 3MoO2 + 12Li+ + 12e-

(3)

In order to further expound the electrochemical process of CMO/C-600, the charge-discharge profiles of CMO/C-600 at 200 mA g-1 are displayed in Figure 5d. In the first cycle, CMO/C-600 delivers a discharge and charge capacity of 1110 and 888 mAh g-1, respectively, with a coulombic efficiency of 80%. The capacity loss is because of the trapping of Li + in the Co2Mo3O8 nanoplates and decomposition of the electrolyte. In the subsequent 2nd, 5th and 10th cycles, the CMO/C-600 exhibits reversible capacities of 922, 902, and 898 mAh g-1, respectively, with coulombic efficiences as high as ~99%. The CMO/C-600 electrode also shows good cycling performance in high current density, as can be seen from Figure 5e. The electrode reveals a quite flat cycling profile at 500 mA g-1 with an initial capacity of 1042 mAh g-1, which maintains at 874 mAh g-1 after 100 cycles. When the current density is increased to 1000 mA g-1, the CMO/C-600 electrode delivers a capacity of 596 mAh g-1 at the end of 100 cycles. The morphology of CMO/C-600 after 100 cycles at 1 A g-1 is shown in Figure S4. Co2Mo3O8 nanoplates were still interconnected by the carbon in CMO/C-


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600 after extended cycling. Due to the influence of PVDF and acetylene black, the transmittance is lowered, resulting in the inability to see Co2Mo3O8 nanoplates in some places. (Figure S4) The XRD pattern of the electrode after cycling, which is shown in Figure S5. The XRD pattern of CMO/C-600 shows that the main peaks are still correspond to Co2Mo3O8 (JCPDS no. 340511), implying the stable crystal structure of CMO/C-600. More importantly, the electrochemical performance of the CMO/C-600 electrode is higher than those of the Mo-based nanomaterials reported in the previous reports, which is listed in Table 1.33-38 Figure S6 reveals the cycling performance of CMO/C-600 and CMO/C-600-1 at 200 mA g-1. The CMO/C-600-1 delivers 410 mAh g-1 after 100 cycles. Apparently, the CMO/C-600 expresses higher capacity and cycling stability, which has potential application in energy storage. Electrochemical impedance spectroscopy (EIS) is carried out to study the kinetics under slight pertubation in the electrochemical cell. Figure 5f shows the nyquist plots of the samples and the equivalent circuit. The results indicate that the contact resistance Rs and charge-transfer resistance Rct of CMO/C500, CMO/C-600 and CMO/C-700 are smaller than those of CMO/C-600-1, implying that the nanohybrids constructed via molten salt-assisted method have high conductivity and can effectively improve the diffusion of Li+ and electrons. Among which, CMO/C-600 has the lowest values of Rs and Rct, further manifesting the good rate performance of CMO/C-600 also come from the higher conductivity and enhanced ion transport.


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Figure 5. Cycling performances of CMO/C-500, CMO/C-600 CMO/C-700 at 200 mA g-1 (a), Rate capabilities (b), CV curves of CMO/C-600 at a scan rate of 0.1 mV s-1 (c), Chargedischarge profiles of CMO/C-600 at 200 mA g-1 (d), Cycling performances of CMO/C-600 at 200, 500, 1000 mA g-1 (e) and EIS analysis of samples (f).


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Table 1 Cycling performances and capabilities of M2Mo3O8 (M=Co, Fe, Mn, Zn) electrodes. Reversible Current Mo3-cluster compounds

specific capacity Voltage range (V)

or composites

density (mA g-1)

(mAh g-1) &

Ref.

cycle number LiYMo3O8

0.005-3.0

30

385 & 120th

Mn2Mo3O8

0.005-3.0

30

205 & 50th

Co2Mo3O8

0.005-3.0

60

790 & 60th

60

954 & 60th

600

729 & 21st

1000

471 & 31st

Co2Mo3O8/rGO

0.005-3.0

a

FLG-Co2Mo3O8

0.005-3.0

180

622 & 50th

a

FLG-Mn2Mo3O8

0.005-3.0

180

530 & 50th

a

FLG-Zn2Mo3O8

0.005-3.0

180

590 & 50th

200

835 & 40th

3000

574 & 1st

200

951 & 40th

1500

672 & 20th

200

1075& 100th

500

874 & 100th

Fe2Mo3Mo8-graphene

Mn2Mo3Mo8-graphene CMO/C-600

0.01-3.0

0.01-3.0 0.01-3.0

1000 a

596 & 100

33 34

35

36

37

th

38

This work

FLG-Few Layered Graphene.


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CONCLUSION In the paper, we reported a facile and scalable method for rational design and configuration of highly crystalized Co2Mo3O8 nanoplates interconnected by coal derived carbon. The molten-saltassisted strategy made the precursor react in the molten state, forming a mutual compound with the coal-based carbon. The packed Co2Mo3O8 nanoplates and the carbon combined to effectively relieve the large volume change during discharge/charge process. Accordingly, the acquired composites exhibit outstanding electrochemical performances with high reversible capacity up to 1075 mAh g-1 after 100 cycles (200 mA g-1) and high rate capability (533 mAh g-1, 4000 mA g-1). These superior electrochemical performance of the composites demonstrate promising application in energy storage. Our work opens up opportunities for the synthesis of a wide variety of oxide-based Li-ion battery anodes.

ASSOCIATED CONTENT Supporting Information. The following files are available free of charge. Additional data including Materials, Characterization, Electrochemical Measurements; Elemental analysis, XPS, EDS mapping, N2 adsorption-desorption isotherms and pore size distribution, TEM and XRD after cycling, cycle performance (PDF)

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]


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Author Contributions S. S. Gao and Y. K. Tang contributed equally to this work. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was subsidized by the National Natural Science Foundation of China (51672235), the National Ten Thousand Talents Program (2017), Science and Technology Talents Training Project of Urumqi, Student Innovation Training Program of Xinjiang University (201710755010) and the Doctoral Innovation Program of Xinjiang University (XJUBSCX-2016009). REFERENCES (1) Armand, M.; Tarascon, J. M. Building Better Batteries. Nature 2008, 451, 652-657. (2) Dunn, B.; Kamath, H.; Tarascon, J. M. Electrical Energy Storage for the Grid: A Battery of Choices. Science 2011, 334, 928-935. (3) Lu, Y.; Yu, L.; Lou, X. W. Nanostructured Conversion-Type Anode Materials for Advanced Lithium-Ion Batteries, Chem 2018, 4, 972-996. (4) Lu, Y.; Yu, L.; Wu, M. H.; Wang, Y.; Lou, X. W. Construction of Complex Co3O4@Co3V2O8 Hollow Structures from Metal-Organic Frameworks with Enhanced Lithium Storage Properties. Adv. Mater. 2018, 30 (1), 1702875-1702880. (5) Dong, J. Y.; Xue, Y. M.; Zhang, C.; Weng, Q. H.; Dai, P. C.; Yang, Y. J.; Zhou, M.; Li, C. L.; Cui, Q. H.; Kang, X. H.; Tang, C. C.; Bando, Y.; Golberg, D.; Wang, X. Improved Li+ Storage through Homogeneous N-Doping within Highly Branched Tubular Graphitic Foam. Adv. Mater. 2017, 29 (6), 1603692-1603699. (6) Guo, C.; He, J. P.; Wu, X. Y.; Huang, Q. W.; Wang, Q. P.; Zhao, X. S.; Wang, Q. H. Facile Fabrication of Honeycomb-like Carbon Network-Encapsulated Fe/Fe3C/Fe3O4 with Enhanced Li-Storage Performance. ACS Appl. Mater. Interfaces 2018, 10, 35994-36001.


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Highly Crystalized Co2Mo3O8 Hexagonal Nanoplates Interconnected

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