hollow graphene spheres composite for high performance lithium-ion battery anodes

hollow graphene spheres composite for high performance lithium-ion battery anodes

Accepted Manuscript Novel design of Fe3O4/hollow graphene spheres composite for high performance lithium-ion battery anodes Ya-Jing Duan, Dong-Lin Zha...

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Accepted Manuscript Novel design of Fe3O4/hollow graphene spheres composite for high performance lithium-ion battery anodes Ya-Jing Duan, Dong-Lin Zhao, Xiao-Hong Liu, Hui-Xian Yang, Wen-Jie Meng, Min Zhao, Xin-Min Tian, Xin-Yao Han PII:

S0925-8388(18)34447-5

DOI:

https://doi.org/10.1016/j.jallcom.2018.11.304

Reference:

JALCOM 48530

To appear in:

Journal of Alloys and Compounds

Received Date: 24 August 2018 Revised Date:

19 November 2018

Accepted Date: 22 November 2018

Please cite this article as: Y.-J. Duan, D.-L. Zhao, X.-H. Liu, H.-X. Yang, W.-J. Meng, M. Zhao, X.-M. Tian, X.-Y. Han, Novel design of Fe3O4/hollow graphene spheres composite for high performance lithium-ion battery anodes, Journal of Alloys and Compounds (2018), doi: https://doi.org/10.1016/ j.jallcom.2018.11.304. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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ACCEPTED MANUSCRIPT

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Novel design of Fe3O4/hollow graphene spheres composite for high performance lithium-ion battery anodes Ya-Jing Duan, Dong-Lin Zhao*, Xiao-Hong Liu, Hui-Xian Yang, Wen-Jie Meng,

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Min Zhao, Xin-Min Tian, and Xin-Yao Han

State Key Laboratory of Chemical Resource Engineering; Key Laboratory of Carbon

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Fiber and Functional Polymers (Beijing University of Chemical Technology),Ministry of Education; Beijing Engineering Research Center of Environmental Material for

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Water Purification; Beijing University of Chemical Technology, Beijing 100029, China

Abstract

On account of its high theoretical capacity and low cost, Fe3O4 is regarded as a

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promising anode material for lithium-ion batteries. Nevertheless, many problems such as poor conductivity and volume expansion during lithiation severely limit its practical

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application. In this work, we synthesized hollow graphene spheres (HGSs) by self-assembly and innovatively combined it with Fe3O4 particles to obtain a composite

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material. The Fe3O4/HGSs composite exhibits excellent electrochemical performances as an anode material, which behaves an initial discharge specific capacity of 1670.8 mA h g-1 at 50 mA g-1 and 1048.5 mA h g-1 after 50 cycles. Especially, the specific capacity can maintain as high as 617.1 mA h g-1 at the current density of 1000 mA g-1, which is

*Corresponding author. Tel.: +86-10-64434914; Fax: +86-10-64434914 Email address: [email protected] (D. L. Zhao) 1

ACCEPTED MANUSCRIPT much higher than that of commercial graphite. While largely inhibiting agglomeration between the particles of Fe3O4 particles, hollow spheres composed of conductive and flexible graphene layers also provide an interconnected conductive network. We believe

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other transition metal oxides for lithium-ion batteries.

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that this design in structure will also provide a new perspective for the researches of

Keywords: Energy storage materials; Electrode materials; Nanostructured materials;

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Oxide materials; Nanofabrications.

1. Introduction

In the 21st century, while enjoying the high-quality life brought about by

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scientific development, human beings have to face growing problems such as energy shortages and environmental pollution. Therefore, the development and application of

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new clean energy have become an urgent priority. Nowadays, lithium-ion batteries play an important role in personal portable devices such as cellular phones and laptops as a

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result of their high energy density, excellent cycle performance and environmental friendliness [1-5]. However, the theoretical capacity of commercial graphite anodes (372 mA h g-1) is too low to meet the growing demand of the application of lithium-ion batteries in modern life [6], which has promoted the exploration of more advanced anode materials, such as silicon [7-9], tin [10-11] and transition metal oxides [12-17]. Among them, research related to Fe3O4 has become one of the most active directions,

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ACCEPTED MANUSCRIPT on account of its advantages of remarkable theoretical capacity, non-toxicity and low cost [18-19]. Nevertheless, Fe3O4 anodes generally exhibit unsatisfactory rate performance, resulting from its poor electrical conductivity [20]. What is more

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troublesome is that the Fe3O4 anodes suffer from huge volume expansion upon cycling. The large volume change will destroy the structure of the material and even cause

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particle pulverization, which is the main reason for the loss of electrical contact and even electrode failure [21-23].

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In order to solve the above problems, one of the viable strategies is to design nano-sized Fe3O4 [24], such as nanorods [25], hollow nanoparticles [26], etc. Nanostructures are believed to effectively shorten the diffusion path of lithium ions, which is very beneficial for accelerating lithium ion transport [27]. In addition,

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nanostructures can release strain caused by volume expansion to a certain extent, ensuring that electrode materials maintain their integrity during cycling. Nevertheless,

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the conditions required for the processing of nanostructures are very rigid, which is unrealistic for practical applications [28]. Furthermore, the agglomeration between

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nanoparticles also has a destructive impact on the cycle performance of the electrode material. The combination of transition metal oxides and carbon materials by surface modification has been considered as one of the significant directions for improving electrochemical performance [29-30]. Therefore, another effective strategy to overcome these shortcomings is to build a composite of Fe3O4 and carbon materials. Among many alternative carbon materials, graphene attracts a lot of attention from researchers due to

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ACCEPTED MANUSCRIPT its high electronic conductivity, good mechanical properties and high thermal conductivity [31]. Ma et al. [32] designed the urchin-like porous Fe3O4 composited with three-dimensional graphene. The porous Fe3O4 particles are tightly wrapped by the

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graphene network, which exhibits an excellent reversible specific capacity and enhanced cycle performance. However, the porous structure with a huge specific surface

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area also promotes the forming of solid electrolyte interphase (SEI), resulting in an increase in irreversible capacity. Zhang et al. [33] developed a one-step synthesis for a

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composite of RGO with tiny Fe3O4 nanoparticles. The composite with excellent electrochemical stability will be an appealing anode material for lithium ion batteries. Inspired by abundant investigations, we synthesized hollow graphene spheres (HGSs) by self-assembly and innovatively combined it with Fe3O4 particles to obtain a

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composite. The hollow graphene sphere with a large specific surface area can effectively inhibit the agglomeration between Fe3O4 particles. Besides, the vast pleats

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on the surface of the graphene sphere provide suitable space for the adhesion of the Fe3O4 particles, ensuring the structural stability of the composite. Moreover, the Fe3O4

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particles are uniformly dispersed on the conductive network composed of graphene, which makes up for the disadvantage of poor conductivity of Fe3O4. Thanks to these advantages in structural design, the Fe3O4/HGSs composite exhibits outstanding electrochemical performances as an anode material for lithium-ion batteries, which also provides a reference for the exploration of other transition metal oxides in lithium-ion batteries.

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ACCEPTED MANUSCRIPT 2. Experimental 2.1. Synthesis of HGSs Hollow graphene spheres were prepared through self-assembly method. Firstly, 100

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mg graphene oxide (GO) was added into 20 ml deionized water, the uniform graphene oxide suspension was obtained by ultrasonication for 2 h. The GO used was made from

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natural graphite through a modified Hummers method. After that, concentrated ammonia was added dropwise until the pH value of the solution reaches 12. Then, the

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above solution was gently added into preheated olive oil (90 °C), followed by stirring for 2 h at 90 °C and 95 °C, respectively. When the emulsion is naturally cooled, the hollow graphene oxide spheres (HGOSs) were obtained by centrifugation, washing with petroleum ether for 3 times and drying at 65 °C. The HGOSs were reduced to HGSs at

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600 °C for 4 h under a gas mixture of Ar and H2 (95:5 v/v). 2.2. Synthesis of Fe3O4/HGSs

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The Fe3O4 particles were prepared according to previously reported in situ reduction [34]. Firstly, 50 mg HGSs was homogeneously dispersed in 150 ml FeCl3 solution

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through ultrasonication for 1 h. After that, the mixture was aged at 80 °C the whole day. The sample obtained by centrifugation was rinsed with deionized water several times, followed by drying under vacuum at 90 °C for 24 h. The obtained powder was placed in a tube furnace at 600 °C for 4 h under N2 atmosphere to result in the Fe3O4/HGSs composite. For comparison, we have carried out a series of experiments by varying the

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ACCEPTED MANUSCRIPT concentration of FeCl3 solution. The prepared samples were denoted as Fe3O4/HGSs-1 (0.025mol/L),

Fe3O4/HGSs-2

(0.05mol/L),

Fe3O4/HGSs-3

(0.10mol/L)

and

Fe3O4/HGSs-4 (0.20mol/L).

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2.3. Characterization

The morphologies of the samples were characterized by scanning electron

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microscope (SEM, Hitachi S-4700). X-ray diffraction (XRD) was conducted on a D/max 2500 V X-ray diffractometer (λ = 1.5406 Å).

The carbon content in the

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composites was estimated by thermogravimetric analysis (TGA, NETZSCH STA 449F3) under air atmosphere between 100 °C to 800 °C, with a heating rate of 10 °C min-1. The electrochemical performances of the Fe3O4/HGSs composite as anode materials for lithium-ion batteries were performed by 2032 type coin cells that were packaged in

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an Ar-filled glovebox. The electrodes contain 80 wt% active material, 10 wt% conductive carbon black as a conductive additive and 10 wt% polyvinylidene fluoride

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(PVDF) as the binder. After thoroughly grinding the above three in a mortar, add an appropriate amount of N-methyl-2-pyrrolidone (NMP) and continue grinding until a

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uniform slurry was obtained. The slurry is evenly coated on copper foil and dried at 80°C in vacuum overnight. The electrolyte solution was 1 M LiPF6 in ethylene carbonate/diethyl carbonate (EC/DEC, 1:1 v/v), with 10 vol% fluoroethylene carbonate (FEC) added to improve the cycling stability. Lithium metal foil was used as the counter electrode. The charging and discharging profiles were conducted using battery test system (LAND, Wuhan) with a voltage window ranged from 0.01 V to 3.0 V. Cyclic

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ACCEPTED MANUSCRIPT voltammogram (CV) was performed using the Versa STAT3 electrochemical workstation produced by Princeton. Electrochemical impedance spectroscopy (EIS) measurements were undertaken by the same electrochemical workstation.

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3. Results and discussion

Fig. 1 shows the synthesis diagram of Fe3O4/HGSs composite. Graphene oxide is

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negatively charged due to the existence of hydrophilic groups such as hydroxyl and carboxyl groups. The W/O emulsion formed as the addition of preheated olive oil. The

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GO nanosheets curled automatically to form a spherical structure, which was driven by electrostatic incorporation. Subsequently, high temperature treatment under hydrogen atmosphere reduces the HGOSs to HGSs. Finally, the composite material was obtained by in situ reduction of iron hydroxide on the surface of the graphite spheres.

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As shown in Fig. 2a and b, the morphology of the HGOSs was characterized by SEM. It can be seen that the size of the spheres is relatively uniform (~30 µm). Besides, the

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broken sphere uncovers that the interior is hollow and the thickness of the wall is in the neighborhood of 1 µm. In addition, the surface of the microspheres is kind of rough. It

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is probably owing to the continued escape of water vapor during the self-assembly process. As shown in Fig. 2c and d, after reduction in hydrogen, most of the resultant hollow graphene spheres (HGSs) can still maintain the original appearance. In the meantime, the surface of the spheres becomes rougher and a large number of pleats appear. This may be due to the generation and evolution of gases during the high temperature reduction process.

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ACCEPTED MANUSCRIPT Fig. 3 displays the SEM images of Fe3O4/HGSs prepared by varying the concentration of FeCl3 solution. As we can see from Fig. 3a, c, e and g, the HGSs still maintain a spherical structure although the synthesis and loading process of Fe3O4

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particles includes a series of experimental steps such as centrifugation and ultrasonic treatment. The surface of HGSs is more or less distributed with Fe3O4 particles. When

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the concentration of FeCl3 solution was 0.025 mol/L, the synthesized Fe3O4/HGSs-1 are shown in Fig. 3a and b. It can be seen from Fig. 3b that the size of the Fe3O4 particles is

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not quite uniform, ranging from tens to hundreds of nanometers. The particles of different sizes are scattered on the surface of the graphene sheet. Due to the low concentration of FeCl3 solution, the number of Fe3O4 particles obtained is less. It may probably suppress the occurrence of agglomeration between Fe3O4 particles to a certain

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extent. When the concentration of FeCl3 solution increased to 0.05 mol/L, the prepared Fe3O4/HGSs-2 was shown in Fig. 3c and d. It is clear that there are more Fe3O4 particles

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in Fe3O4/HGSs-2 than that in Fe3O4/HGSs-1. In addition, Fig. 3d reveals that the obtained Fe3O4 particles are comprised of nanocubes of 300-500 nm. These particles of

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uniform shape and size are semi-embedded in the pleats on the surface of spherical graphene without obvious agglomeration, which is very favorable for maintaining the structural stability of the electrode material in the case of large bulk expansion of Fe3O4 particles due to lithium intercalation. Fig. 4 shows the uniform distribution of iron, oxygen, and carbon element, suggesting that the Fe3O4 particles are well dispersed on the surface of the hollow graphene spheres. When the concentration of FeCl3 solution

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ACCEPTED MANUSCRIPT was further increased to 0.10 mol/L, the obtained Fe3O4/HGSs-3 are shown in Fig. 3e and f. It can be seen that the layers and edges of the spherical graphene are almost completely covered by a large amount of Fe3O4 particles. The appearance of these

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particles is no longer regular and the particle size is smaller than that of Fe3O4/HGSs-2. Even more noteworthy is that these particles are tightly packed with each other, and

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some of them even stick together. This will undoubtedly bring significant challenges to the electrode material in maintaining its original appearance during charge and

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discharge cycles. It can be seen from Fig. 3g and h that Fe3O4/HGSs-4, which arises from the FeCl3 solution with a concentration of 0.20 mol/L, shows a more dense distribution of Fe3O4 particles compared with Fe3O4/HGSs-3. Large numbers of irregularly shaped Fe3O4 particles are stacked on top of one another, completely

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covering the exposed surface of spherical graphene. Since the concentration of ferric chloride is so large that hollow spheres made of the relatively low content of graphene

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cannot effectively inhibit agglomeration between the Fe3O4 particles. It goes without saying that the structural instability during the intercalation/delithiation reaction caused

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by the agglomeration phenomenon has a negative effect on the electrochemical performance.

Fig. 5 displays the X-ray diffraction patterns of graphene oxide (GO), HGOs and HGSs. A sharp peak is seen at 2θ values of 11.56°, corresponding to the characteristic diffraction peak (002) of GO. It indicates that the d-spacing of GO is 0.765 nm, which results from the interaction between the water molecules and the formation of a large

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ACCEPTED MANUSCRIPT number of oxygen-containing functional groups between the sheets of graphite during the intense oxidation process. Compared with GO, the diffraction peak intensity of the HGOs formed by the self-assembly process is greatly weakened, which may be due to

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the role of ammonia to remove some oxygen-containing functional groups and water molecules. At the same time, the diffraction peak (002) is seen in the X-ray diffraction

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pattern of HGOs, indicating that the graphene sheets were rearranged during the formation of hollow spheres. After the high-temperature treatment under hydrogen, the

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characteristic diffraction peak (001) of GO completely disappeared, suggesting that the reduction reaction proceeded exactly as expected. Fig. 6 demonstrates the X-ray diffraction patterns of Fe3O4/HGSs, which arise from FeCl3 solution of different concentrations. The diffraction patterns of Fe3O4 match well with the standard XRD

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pattern (JCPDS 75-0033). To be specific, the diffraction peaks at 2θ = 30.28°, 35.68°, 43.4°, 53.8°, 57.38° and 62.96°can be attributed to (220), (311), (400), (422), (511) and

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(440) reflections, respectively. The TGA results show that the weight percentage of carbon in Fe3O4/HGSs-1, Fe3O4/HGSs-2, Fe3O4/HGSs-3 and Fe3O4/HGSs-4 is 18.2 %,

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14.7 %, 11.2 % and 8.8 % respectively, which is positively correlated with the concentration of FeCl3 solution. The as-prepared Fe3O4/HGSs composite material was used as anode electrode materials for lithium ion batteries and Fig. 7-11 shows the electrochemical properties. Cyclic voltammogram (CV) of the Fe3O4/HGSs composite was tested between 0.01 and 3 V at a scan rate of 0. 1 mV s-1. As shown in Fig. 7, CV curves of the first three cycles

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ACCEPTED MANUSCRIPT show several redox peaks, corresponding to the lithiation/delithiation process during discharge and charge, respectively. There is a clear reduction peak near 0.47 V in the first cathodic scan, which can be interpreted as due to the reduction of Fe3O4 by the

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conversion reaction [Fe3O4 + 8Li+ + 8e- ←→ 3Fe0+ 4Li2O], accompanying with the irreversible decomposition of the electrolyte. It is worth noting that the cathodic peak

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moves to a high voltage value (0.96 V) in the subsequent cycles, which can be attributed to structural change of the electrode material due to the initial insertion of lithium ions.

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In the first anodic scan, a broad peak around 1.68 V is observed at around, corresponding to the process of re-oxidation of Fe0. We find that this broad peak is actually the result of partial overlapping of two peaks, corresponding to the formation of Fe3+ and Fe2+, respectively. However, the voltage values associated with the two

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oxidation reactions are too close to partially overlap. As can be seen in Fig.8, the charge-discharge profiles of the electrode materials for

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diverse cycles were presented at a current density of 50 mA g-1. It can be seen that the initial discharge specific capacities of Fe3O4/HGSs-2 is 1670.8 mA h g-1. The voltage

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corresponding to the discharge platform in the initial charge-discharge profiles also corresponds to the peak of the CV curve. Besides, the first charge specific capacity 1085.9 mA h g-1. The large irreversible capacity of the first cycle results in a relatively low initial coulomb efficiency, which can be mainly attributed to the forming of SEI film. In the subsequent cycles, the profiles begin to show relatively good coincidence. Fig. 9 presents the discharge/charge cycling performances of the composite electrode

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ACCEPTED MANUSCRIPT materials obtained by varying the concentration of FeCl3 solution at the current density of 50 mA g-1. In comparison, Fe3O4/HGSs-2 prepared when the concentration of FeCl3 solution was 0.05mol/L exhibits the highest initial discharge specific capacity (1670.8

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mA h g-1). At the same time, its initial coulomb efficiency (64.99 %) is slightly higher than the other three samples. It is mainly due to the fact that the particle size and shape

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of Fe3O4 particles in Fe3O4/HGSs-2 are relatively regular, so that the formed SEI film is also relatively thin and uniform, resulting in the relatively less irreversible consumption

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of lithium. It can be seen from Fig. 9 that the coulomb efficiencies show an increasing trend and eventually stay above 98% as the number of cycle increases, which suggests that the synthesized composite electrode materials have excellent electrochemical reversibility. During the following 50 cycles, the discharge specific capacity of the

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composite electrode materials shows slow decay tendency. After 50 cycles, discharge specific capacities of Fe3O4/HGSs-1, Fe3O4/HGSs-2, Fe3O4/HGSs-3 and Fe3O4/HGSs-4

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can maintain at 696.6 mA h g-1, 1048.5 mA h g-1, 766.5 mA h g-1 and 848.9 mA h g-1 respectively. By comparison, the cycle stability of Fe3O4/HGSs-2 is much better with

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the retention of 62.75 % relative to the initial capacity at the 50th cycle. The superior cycle stability of Fe3O4/HGSs-2 can be attributed to the homogeneous distribution of Fe3O4 particles on the surface of the hollow graphene spheres, which is much better than that of many other carbon-based Fe3O4 composites, as shown in Table 1. The comparison of the rate performances of Fe3O4/HGSs-1, Fe3O4/HGSs-2, Fe3O4/HGSs-3 and Fe3O4/HGSs-4 composite electrode materials is demonstrated in Fig.

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ACCEPTED MANUSCRIPT 10. The reversible specific capacity of Fe3O4/HGSs-2 composite is 992.9 mA h g-1 after 10 cycles at 50 mA g-1, 912.8 mA h g-1 after 10 cycles at 100 mA g-1, 847.3 mA h g-1 after 10 cycles at 200 mA g-1, 761.5 mA g-1 after 10 cycles at 500 mA g-1, 617.1 mA h

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g-1 after 10 cycles at 1000 mA g-1, respectively. When the current density returns to the original 50 mA g-1, Fe3O4/HGSs-2 composite electrode material still can deliver a

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relatively high specific capacity (940.6 mA h g-1), which is much better than the other three samples. It is enough to show that the structure of Fe3O4/HGSs-2 is so steady that

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it can endure rapid charging/discharging cycles at high current density.

Fig. 11 compares the Nyquist plots before cycling of Fe3O4/HGSs-1, Fe3O4/HGSs-2, Fe3O4/HGSs-3 and Fe3O4/HGSs-4, which are obtained by electrochemical impedance spectroscopy measurements (EIS). In the high frequency region, all of the four samples

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showed a semicircle, which can represent the relative magnitude of the charge transfer impedance (Rct) between the electrode and the electrolyte interface. In addition, the

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slant line in the low frequency region characterizes the impedance related to the diffusion of lithium ions into the active material (Re). It can be seen from Fig.10 that the

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two impedances of the second sample are significantly smaller than the other three samples, suggesting that the structure in which such hollow graphene spheres are combined with uniform Fe3O4 particles is advantageous both for charge transport and ion diffusion. In summary, the excellent electrochemical performance of Fe3O4/HGSs composite can be ascribed to the following factors. First of all, the hollow graphene sphere with a

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ACCEPTED MANUSCRIPT large specific surface area can effectively inhibit the agglomeration between Fe3O4 particles. The Fe3O4 particles are well dispersed on the surface of the hollow graphene spheres so that the overall morphology of the electrode material does not undergo

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catastrophic changes in the case of volume expansion of the particles caused by lithium intercalation. Secondly, the numerous irregular pleats on the surface of the hollow

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graphene spheres facilitate the adhesion of Fe3O4 particles. The particles are semi-embedded on the surface of the spheres, which makes the structure of the obtained

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composite material is so steady that it can withstand the impact of lithium ion shuttling back and forth during cycling. Finally, graphene with ultra-high conductivity provides an interconnected conductive network, which can significantly reduce contact resistance and ensure efficient electron and lithium ion carriage. Moreover, when the morphology

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and quantity of Fe3O4 particles were controlled by varying the concentration of FeCl3

the composite. 4. Conclusion

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solution, we found a synthetic formulation that maximized the structural advantages of

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Fe3O4/HGSs composite was successfully fabricated by self-assembly of graphene oxide and in situ reduction of iron hydroxide. When used as anodes for lithium-ion batteries, the resulting composite electrode material exhibits a large initial discharge specific capacity (1670.8 mA h g-1 at 50 mA g-1), enhanced cycle stability (1048.5 mA h g-1 after 50 cycles) and excellent rate performance, which can be attributed to several features in the structural design. Hollow spheres composed of conductive and flexible

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concentration of FeCl3 solution corresponding to Fe3O4 particles of uniform shape and size by the control variable method and confirmed its effect on the electrochemical

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performances of the composite. More valuable is that this successful structural design can also be extended to the researches of other transition metal oxides for lithium-ion

Acknowledgments

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batteries.

This work was supported by the National Natural Science Foundation of China (Grant 51572012)

and

(20120010110001). References

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fabrication and application in high-performance LiFePO4 cathode materials, J. Mater. Chem. A, 6 (2018) 1057-1066.

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Figure Captions:

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Fig. 1. Schematic diagram for the preparation of Fe3O4/HGSs composite. Fig. 2. SEM images of HGOSs (a, b) and HGSs (c, d).

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Fig. 3. SEM images of Fe3O4/HGSs-1(a, b), Fe3O4/HGSs-2 (c, d), Fe3O4/HGSs-3(e, f) and Fe3O4/HGSs-4(g, h).

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Fig. 4. SEM, elemental mapping images of Fe3O4/HGSs-2. Fig. 5. XRD patterns of GO, HGOSs and HGSs. Fig. 6. XRD patterns of Fe3O4/HGSs-1 (a), Fe3O4/HGSs-2 (b), Fe3O4/HGSs-3 (c) and Fe3O4/HGSs-4 (d). Fig. 7. The CV curves of Fe3O4/HGSs-2. Fig. 8. Discharge-charge curve of Fe3O4/HGSs-2 at a current density of 50 mA g−1.

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Fig. 11. Nyquist plots of impedance for Fe3O4/HGSs.

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Table Caption:

Table 1 A summary of recent reports on various carbon-based Fe3O4 composites with

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this work.

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Cycle number

Fe3O4/HGSs

50

50

Fe3O4/GNSs

92.5

50

Fe3O4/graphene

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[email protected] nanospheres

300

Fe3O4/C composite Fe3O4/C composite microrods

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1048.5

This work

∼605

[24]

30

1026

[34]

80

736

[35]

92.6

65

907

[36]

100

100

596

[37]

200

100

∼650

[38]

100

40

~1000

[39]

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porous [email protected]

Ref.

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Fe3O4/graphene composite

Holding capacity (mA h g-1)

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Current density (mA g-1)

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Table 1 A summary of recent reports on various carbon-based Fe3O4 composites with this work.

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Fig.1. Schematic diagram for the preparation of Fe3O4/HGSs composite.

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Fig.10. Rate performance of Fe3O4/HGSs at different current densities.

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Fig.11. Nyquist plots of impedance for Fe3O4/HGSs.

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Fig.2. SEM images of HGOSs (a, b) and HGSs (c, d).

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Fig.3. SEM images of Fe3O4/HGSs-1 (a, b), Fe3O4/HGSs-2 (c, d), Fe3O4/HGSs-3 (e, f) and Fe3O4/HGSs-4 (g, h).

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Fig.4. SEM, elemental mapping images of Fe3O4/HGSs-2.

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Fig.5. XRD patterns of GO, HGOSs and HGSs.

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Fig.6. XRD patterns of Fe3O4/HGSs-1 (a), Fe3O4/HGSs-2 (b), Fe3O4/HGSs-3 (c) and Fe3O4/HGSs-4 (d).

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Fig.7. The CV curves of Fe3O4/HGSs-2.

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Fig.8. Discharge-charge curve of Fe3O4/HGSs-2 at a current density of 50 mA g−1.

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Fig.9. Cycling performance of Fe3O4/HGSs at a current density of 50 mA g−1.

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Highlights Paper Title: :Novel design of Fe3O4/hollow graphene spheres composite

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for high performance lithium-ion battery anodes

• Fe3O4/HGSs composite was successfully fabricated by self-assembly of graphene

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oxide and in situ reduction of iron hydroxide.

• The electrochemical performances of Fe3O4/HGSs composite are affected by the

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concentration of FeCl3 solution.

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• Fe3O4/HGSs composite exhibits excellent lithium storage performance.