Facile synthesis of α[email protected] hollow spheres as ultra-long cycle performance anode materials for lithium ion battery

Facile synthesis of α[email protected] hollow spheres as ultra-long cycle performance anode materials for lithium ion battery

Accepted Manuscript Facile synthesis of α[email protected] hollow spheres as ultra-long cycle performance anode materials for lithium ion battery Ruiping Liu, ...

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Accepted Manuscript Facile synthesis of α[email protected] hollow spheres as ultra-long cycle performance anode materials for lithium ion battery Ruiping Liu, Chao Zhang, Qi Wang, Chao Shen, Yufen Wang, Yue Dong, Ning Zhang, Miaomiao Wu PII:

S0925-8388(18)30270-6

DOI:

10.1016/j.jallcom.2018.01.262

Reference:

JALCOM 44726

To appear in:

Journal of Alloys and Compounds

Received Date: 26 September 2017 Revised Date:

7 January 2018

Accepted Date: 19 January 2018

Please cite this article as: R. Liu, C. Zhang, Q. Wang, C. Shen, Y. Wang, Y. Dong, N. Zhang, M. Wu, Facile synthesis of α[email protected] hollow spheres as ultra-long cycle performance anode materials for lithium ion battery, Journal of Alloys and Compounds (2018), doi: 10.1016/j.jallcom.2018.01.262. 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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Facile Synthesis of α[email protected] Hollow Spheres as Ultra-long Cycle Performance Anode Materials for Lithium Ion Battery

Abstract

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Ruiping Liua*, Chao Zhang a, Qi wang a, Chao Shena, Yufen Wangb*, Yue Donga, Ning Zhanga, Miaomiao Wua a Department of Materials Science and Engineering, China University of Mining & Technology (Beijing), Beijing 100083, China b Energy & Materials Engineering Center, College of Physics and Materials Science, Tianjin Normal University, Tianjin 300387, China

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The hollow α-Fe2O3 with spherical morphology has been successfully synthesized via citric acid

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assisted hydrothermal synthetic method, and then the core-shell α[email protected] can be obtained through annealing process after carbon coating. The morphologies and structure of the samples were characterized by means of SEM, TEM, EDS, XRD, Raman and XPS. The results show that the α[email protected] hollow spheres deliver high reversible lithium storage capacity and good cycling

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stability (initial discharge/charge specific capacity of 1377mAh/g and 723mAh/g at 1C, discharge specific capacity maintain 793.2mAh/g after 600 cycles) and superior rate performance (997.8 mAh/g at 0.1 C, 943.8 mAh/g at 0.2 C, 829.2 mAh/g at 0.5 C, 764.8 mAh/g at 1 C, and 697.6 mAh/g

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at 2 C, and more importantly, when the current density returns to 0.1 C, a capacity of 966.3 mAh/g

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can be recovered). The hollow structure of α[email protected] not only alleviates the volume change during cycling, but also facilitates Li-ion and electron transport, and stabilizes the SEI layer. These results suggest that α[email protected] hollow spheres are a promising anode material for lithium ion batteries.

Keywords: Lithium Ion Battery, α-Fe2O3, hollow spheres, Cycle Performance

*Corresponding authors. Ruiping Liu, Tel.: +86 10-62339175, fax: +86 10-62339081, E-mail address: [email protected] 1

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1. Introduction Lithium-ion batteries (LIBs) have attracted more and more attention due to the dominant

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position of potential power sources in portable electronic devices, hybrid electric vehicles and electric vehicles [1, 2]. In particular, the increasing demand in enhancing the battery life of electric vehicles

has stimulated

much

enthusiasm

for exploiting electrode

materials

with

high

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electrochemical performance [3]. As a vital part of the LIBs, anode materials made an outstanding contribution to improve the energy density of LIBs. However, due to the relative low theoretical

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capacity (372mAh/g) and safety issues of the commercial available graphite-based anode materials, it is highly desirable to develop new type anode materials with improved electrochemical performance [4, 5].

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Among all the potential candidates of anode materials, due to its much higher theoretical capacity (1007mAh/g), abundance, nontoxicity, low cost and environmental benignity, α-Fe2O3 has been highly thought one of the most promising anode materials for lithium ion battery with

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ultra-long cycle performance [6-9]. However, large volume expansion during lithiation process

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(~96%) and poor electronic conductivity are the two mainly factors to hinder the practical application of α-Fe2O3 anode materials [9-11]. In order to address the above problems, several strategies have been successfully applied to repress the volume expansion and enhance the electric conductivity of α-Fe2O3, such as introducing pores into α-Fe2O3, designing various α-Fe2O3 nanostructure and preparing the α-Fe2O3/carboneous material hybrids [12-14]. Due to its unique structure and high specific surface area, hollow spheres have attracted tremendous attention in the field of drug delivery, gas sensor and energy storage and conversion [15, 16]. The free space in

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ACCEPTED MANUSCRIPT hollow spheres not only can accommodate the huge volume change during charging process, but also reduce the diffusion path of lithium ions, and thus improve the electrochemical performance of the LIBs [17]. However, compared to other metal oxide, there is little report on α-Fe2O3 hollow spheres

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as anode materials for LIBs, and moreover, the synthesis of the state-of-the-art α-Fe2O3 hollow spheres usually involves complicated procedures and expensive sacrificial templates [7, 18]. Thus,

improved electrochemical performance becomes essential.

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the development of a simple, economic and scalable method to prepare α-Fe2O3 hollow spheres with

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Herein, we design α[email protected] hollow spheres which was prepared through coating carbon layer on the surface of α-Fe2O3, in which α-Fe2O3 was prepared by hydrothermal process with the aid of citric acid. The structural and morphologies of the spheres were investigated, and the electrochemical performance of the as-obtained α[email protected] and pure α-Fe2O3 hollow spheres were compared.

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2. Experimental methods

2.1 Synthesis of α[email protected] hollow spheres

In a typical synthesis, 1.08g of FeCl3·6H2O was dispersed in 100mL mixed solution contains

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deionized water and absolute ethanol (volume ratio1:1) with the assistance of ultrasound (11KW,

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30min) to form a homogeneous solution, followed by adding 0.2g of citric acid under magnetic stirring to gain orange transparent solution, and then transferred into the 100mL Teflon stainless steel autoclave maintained at 180°C for 24 h. The precipitates were collected by centrifugation and washing several times with deionized water and absolute ethanol alternately after being cooled to room temperature spontaneously. Finally the obtained brick-red powder was dried at 80°C for 12 hours in air. To obtain α[email protected] hollow spheres, 0.5g of α-Fe2O3 was dispersed in the 100mL of Tris-HCL

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ACCEPTED MANUSCRIPT buffer solution (pH=8.5) containing 500mg of dopamine hydrochloride under vigorous magnetic stirring for 12h, and then the product was collected after centrifugation, washing and drying. Eventually, the brown product was heated to different temperature at a rate of 5°C/min and

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maintained for 4 h under the Ar atmosphere to convert the dopamine polymers into amorphous carbon. The sample calcined at 300°C, 350°C, 400°C and 600°C was named as α-FC-300, α-FC-350, α-FC-400 and α-FC-600, respectively.

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2.2 Characterization

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The structure and morphology of as-prepared powders were measured by XRD (Bruker D8-Advance diffractometer), TEM (JEOL JEM-2100, operated AT 200KV) and SEM (Zeiss Supra 40 FE). X-ray photoelectron spectroscopy (XPS) (Kratos AXIS UItra DLD; Al (anode) X-ray source) was utilized to investigate the surface chemistries of the as-prepared materials. The thermal

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properties of the as-prepared sample were performed by TGA over a temperature range of 25-800°C with a ramp rate of 10°C /min in air. The element distribution was measured by energy dispersive spectroscopy (EDS) which was carried on the SEM. The degree of crystallization of carbon in

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α[email protected] hollow spheres was measured by Raman spectroscopy. Brunner−Emmet−Teller (BET)

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surface area was measured by N2 adsorption at liquid nitrogen temperature using a NOVA4000 automated gas sorption system, the degas temperature is 300°C. The pore size distribution of samples was obtained from desorption branch by the Barrett–Joyner–Halenda (BJH) method. 2.3 Electrochemical measurement The working electrode was prepared by mixing the active material, carbon black and polyvinylidene fluoride (PVDF) with the weight ratio of 8:1:1. The lithium metal foil and microporous polypropylene film was used as counter electrode and separator, respectively. 1 M

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ACCEPTED MANUSCRIPT LiPF6 dissolved in ethylene carbonate (EC)/diethyl carbonate (DEC) / dimethyl carbonate (DMC) (1:1:1 by volume) was selected as electrolyte. The coin cell with the areal density of 0.368 mg/cm2 was assembled in a glove box full filled with Ar. The electrochemical performance tests were

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performed by using LAND electric battery test system after aging for 5h. The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were carried out on an electrochemical workstation (CHI660C, Shanghai Chenhua). The CV was performed at a scan rate of 0.1 mV/s. EIS

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measurements were recorded over the frequency range from 100 kHz to 0.01 Hz.

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3. Results and Discussion

The crystalline structure and phase of the α[email protected] hollow spheres was investigated by XRD, as shown in Fig.1. It can be clearly seen that all of the samples are well-crystallized. X-ray diffraction pattern of α-FC-300 shows several broad peaks, which is the character of hexagonal

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hematite α-Fe2O3 (JCPDS No.33-0644), indicating that the existence of carbon layer have no effect on the structure of α-Fe2O3 and the carbon presented in the forms of amorphous when calcined under 300°C. With increasing the calcination temperature to 350°C, X-ray diffraction results of α-FC-350

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demonstrates the constituent of α[email protected] has changed during the calcination process, and both

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α-Fe2O3 and Fe3O4 were detected. Therefore, it can be deduced that hematite α-Fe2O3 are easily transformed to Fe3O4 by reacting with the outer carbon layers during the annealing process [19]. In order to further confirm the influence of the annealing temperature on the constituent of carbon coated iron oxide, we continue to increase the annealing temperature to 400°C and 600°C. It can be seen that all of the Fe3+ in α-FC-400 and α-FC-600 was converted to Fe2+, which exists in the forms of Fe3O4. The above results indicate that α-Fe2O3 will transform into Fe3O4 gradually with elevating the annealing temperature. As a consequence, the critical annealing condition of the phase

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ACCEPTED MANUSCRIPT transformation from α-Fe2O3 to Fe3O4 is about 350°C for 4h. In this work, we employed this critical condition to annealing α[email protected] to obtain the α-FC-300 with higher thermal stability and better

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crystalline.

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Fig.1 XRD pattern of α- [email protected] calcined at different temperature.

The α-Fe2O3 hollow spheres have been successfully synthesized via hydrothermal method. The

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schematic illustration of the formation of α-Fe2O3 and α[email protected] hollow spheres is shown in Fig.2. The shape and particle size of α-Fe2O3 can be readily adjusted and controlled by varying the

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concentration of citric acid, as shown in Fig. S1. The mechanism of adjusting the morphology is ascribed to the existence of citric acid which is organic acid with a large number of carboxyl and hydroxyl groups. The hydroxyl groups are conductive to nanoparticles self-assembly to form special spherical morphology. Figure S2 shows the SEM images of the samples with different hydrothermal time. It can be seen that the small particles formed at the very beginning of the hydrothermal process, with increasing of the hydrothermal time, small particles aggregate to form solid spheres under the function of citric acid, and which will finally turn into hollow spheres due to the Ostwald ripening 6

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with the prolonged hydrothermal process.

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Fig.2 Schematic illustration of the formation of α-Fe2O3 spheres (a) and α[email protected] spheres (b)

Fig.3 SEM images of α-Fe2O3 spheres before (a) and after (b) carbon coating

Figure 3 shows the morphologies of the α-Fe2O3 spheres before and after coating a thin carbon layer generated by dopamine hydrochloride. It can be seen that the samples before carbon coating are perfectly spherical, monodisperse with diameter of 200-300 nm, while after carbon coating, the 7

ACCEPTED MANUSCRIPT diameter of the spheres increased. EDS mapping images in Figure S3 show enrichment of Fe and O signals in the core and homogeneous distribution of C signal in the shell, further confirming the double-shell configuration of α-FC-300.

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Furthermore, the hollow structure of [email protected] and pure a-Fe2O3 are characterized by TEM, as shown in Fig. 4. We can see that the a-Fe2O3 hollow spheres have a uniform dispersion in size with an average diameter of 200 nm, and the carbon forms a coating layer with a thickness of 30nm that

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continuously wraps a-Fe2O3 hollow spheres Fig.4 (a-b). Such continuous carbon layers may

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effectively improve the structural stability and enhance the electrical conductivity of a-Fe2O3 during the charge/discharge process. The HRTEM image shown in Fig.4(c) displays the lattice fringes of the inner a-Fe2O3 crystals. The lattice space of 0.252 nm are in good accordance with d-values of the (110) planes of a-Fe2O3, which also confirms high crystallinity of a-Fe2O3 in the [email protected] The

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spheres are single crystalline.

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strong spots of the SAED patterns depicted in the inset of Fig. 4(d) confirm that a-Fe2O3 hollow

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Fig.4 The TEM images of a-Fe2O3 spheres (a) and a-Fe2O3 @C (b), the lattice space (c) and SAED

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patterns of a-Fe2O3 (d) of a-Fe2O3

In order to further verify the chemical valence state of the element in hollow spheres, X-ray photoelectron spectroscopy (XPS) test was applied to characterize the chemical characteristics of Fe, O and C on the surface of the α-FC-300, as shown in Fig.5. The photoelectron lines at a binding

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energy of about 285 and 532eV shown in Fig.5 (a) can be ascribed to the C 1s and O 1s, respectively. There is nearly an absence of the Fe2p signals, indicating that the α-Fe2O3 was entirely encapsulated

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with the carbon shells. The existence of Fe (III) in α-FC-300 hollow spheres is evidenced by a satellite peak observed between Fe2p 3/2 (711.08eV) and Fe2p 1/2 (724.73eV), which can be

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assigned to entirely Fe (III) species according to literature [20]. The C 1s spectrum ranging from 280eV to 295eV in Fig.5 (b) can be fitted to carbonyls carbon (C=O, 288.0eV), epoxy hydroxyls (C-O, 286.6eV), sp3-hybridized carbon (C-C, 285.5eV) and sp2-bonded carbon (C-C, 284.6eV). The O 1s spectrum ranging from 527eV to 540eV in Fig.5 (c) can be disassembled into three components, including C-O (531.6eV), C=O (532.1eV) and O2− (530.1eV). Whereas, the C=O and C-O peaks fade away after annealing, and the O2− peaks turned into the dominant one, suggesting an increased component of crystalline α-Fe2O3 in α-FC-300. 9

ACCEPTED MANUSCRIPT (a)

C 1s

Fe 2p3/2

(b)

Fe 2p1/2

Intensity (a.u)

Intensity (a.u)

satellites O1s

740

730

720

710

N1s

700

3

C-C(SP ) 2

C-O

C-C(SP )

C=O

1200

1000

800

600

400

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Fe2p

290

200

285

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(c)

Intensity (a.u)

280

Binding Energy(eV)

Binding Energy(eV)

O2-

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α-Fe2O3

O2-

α[email protected] 540

535

530

525

Binding Energy(eV)

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Fig.5 (a) Typical XPS survey spectrum of α-FC-300, the inset is a high-resolution scan of the Fe 2p spectrum region. (b) C1s XPS spectra of α-FC-300 and (c) O 1s XPS spectra of α-Fe2O3 and α-FC-300 sample.

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Raman spectrum shown in Figure S4 (a) contains two distinguishable peaks named D-band (at about 1362 cm-1) and G-band (at about 1580 cm-1). The ratio of the peak intensity (ID/IG=0.84)

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indicates a relatively low degree of crystallization of carbon in the α-FC-300 samples, which may be conductive to accelerate the diffusion rate of electrons in the α-FC-300 samples[21]. As shown in TGA curves (Fig. S4 (b)), the sample has a small weight loss below 150°C, which is ascribed to the evaporation of water. As the temperature increases to 480°C, the sample exhibits a dramatically weight loss around 31.2wt%, which is ascribed to the pyrolyzation of carbon encapsulated on the surface of α-Fe2O3, and thus the amount of α-Fe2O3 in α-FC-300 is around 69%. The N2 adsorption-desorption isotherm exhibits a distinct large hysteresis loop, which is the typical 10

ACCEPTED MANUSCRIPT characteristic of mesoporous materials, namely a type IV isotherm with H1-shaped hysteresis loop assigned to mesoporous structure (Figure S4(c)). The specific surface area and average pore size of the as-obtained α-FC-300 is 104.9 m2/g and 2.18nm, respectively. The hierarchical porous structure

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of both hollow core and mesopore distributed on the shell may benefit for the lithium ion diffusion process by shorten the diffusion distance due to the relative large contact area between the anode

volume effect during the charge-discharge process.

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materials and liquid electrolyte. Meanwhile, the unique porous structure could also alleviate the

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The galvanostatic charge-discharge test was utilized to further study the electrochemical behavior of α-FC-300 hollow spheres. The discharge-charge potential versus capacity profiles of the different cycles (1st, 10th, 50th, 100th, 170th) were delineated in the Fig.6(a) in the potential window of 0.01~3V(vs. Li+/Li)at a current density of 0.1C. The curves of α-FC-300 present similar features to

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those of nanosized α-Fe2O3 reported previously [19]. The initial discharge/charge capacity are 1325.4mAh/g and 845.4mAh/g with the initial columbic efficiency of 63.8%. In the 1st cycle, the first discharge slope of α-FC-300 hollow spheres appears around at 1.5V, on the behalf of α-Fe2O3

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converted into α-LixFe2O3 [22-24]. Then an evident plateau appears at approximately 0.8~1.0V,

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which stands for the transformation among rhombohedral α-LixFe2O3, cubic Li2Fe2O3 and Fe [25, 26]. Eventually, the voltage gradually decreases from 0.8V to 0.01 V .However the first cycle has a large amount of irreversible capacity loss arise from the formation of solid electrolyte interface (SEI) and Li2O. Moreover, the unusual phenomenon come out is that the initial discharge specific capacity much higher than the theoretical capacity of α-Fe2O3 (1007mAh/g) which was reported by the literature [27]. The extra initial capacity may be due to the further lithium storage via interfacial reaction between the metal and Li2O phase boundary [28].

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ACCEPTED MANUSCRIPT Fig.6 (b) shows the comparison of the cycle performance between α-Fe2O3 and α-FC-300 sample as anodes materials for lithium ion battery at the current density of 1C. Evidently, the cyclability of α-FC-300 electrode is dramatically improved compared to the α-Fe2O3 electrode

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without carbon layer. The α-FC-300 manifests a high initial discharge/charge specific capacity of 1377mAh/g and 723mAh/g with the initial columbic efficiency of 52.5%, and the relative low efficiency is attributed to the formation of SEI layer. However, the columbic efficiency increased to

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92% and subsequently remain stable above 95% after the 2nd cycle, manifesting the benign reversible

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Li+ intercalation/extraction performance. The α-FC-300 hollow spheres exhibits unusual cycle performance due to the capacity decay in the first 260 cycles, after then the capacity increases significantly and up to 793.2 mAh/g after 600th cycle. Analogous results has been reported for [email protected] nanorods [28]. The capacity decay for α-FC-300 in the first 260th cycles should be

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belonged to the pulverization of original α-FC-300 hollow spheres during the lithium ion intercalation/extraction process. It will result in the loss of electrical connectivity between current collector and active materials, and finally deteriorate the cycling performance. Fortunately,

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with the aid of the exterior carbon layer, the dissolution and mechanical failure of these particles can

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be effectively prevented. The inner α-Fe2O3 of the α-FC-300 became smaller and smaller ascribed to the electrochemical milling effect, which will increase the surface area of the active material. Therefore, after 260 cycles, the α-FC-300 show an apparently increase in reversible capacity, which is considered as the activated process reported by Zhang [28]. The lithium storage properties of α-FC-300 hollow spheres at high rate are also investigated and demonstrated an excellent cycling performance. Unfortunately, there is invariably a capacity decay sharply shown in the Fig.6(c) after adjusting the current density from lower to higher, which can be

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ACCEPTED MANUSCRIPT attributed to the concentration polarization of Li+ in the α-FC-300 electrode originating from a diffusion limited process. It can be clearly detected that the amazing initial discharge/charge specific capacity of 997.8 mAh/g and 984.2 mAh/g acquired at the current density of 0.1C, with increasing of

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the current density from 0.2C, 0.5C and 1C to 2C, the discharge capacity of 943.8 mAh/g, 829.2 mAh/g, 764.8 mAh/g, 697.6 mAh/g can be obtained respectively. Moreover, the discharge capacity of 966.3 mAh/g with only a small capacity fade relative to the first 10 cycles can be regained after

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the current density recovered to 0.1C, indicating the superior rate performance. The excellent

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electrochemical property of α-FC-300 electrode can be attributed to the exterior carbon layer, which can enhance the conductivity of electrode as well as buffer the volume expansion of α-Fe2O3 nanocrystals during the repeated lithiation processes.

In the EIS spectra (Fig.7), there is a semi-circle in the high-medium frequency range and

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followed by the inclined line in the low frequency range. The former is attributed to the charge transfer process and associated with the capacitance of the interface between electrolyte and electrode, while the latter can be ascribed to the Warburg impedance and associated with the lithium

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ion diffusion process within the electrode materials. Here, Rs and Rct are the ohmic resistance and the

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charge transfer resistance of the electrodes, respectively. CPEd1 is the constant phase element of electric double layer between the electrolyte and electrode interface, CPE2 and RSEI are parallel connection of capacitance and resistance of lithium ion mobility through SEI layer. W is the Warburg impedance related to the lithium ion diffusion process in the anode materials. The main fitted parameters of each anode were listed in Table S1. It is apparent that the values of Rs and RSEI of α-FC-300 and α-Fe2O3 samples are similar, but the values of Rct and the Warburg admittance coefficient are different from each other. The Rct value of α-FC-300 (179.5Ω) is much lower than that

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ACCEPTED MANUSCRIPT of pure α-Fe2O3 (237.8Ω), which indicates that the α-FC-300 electrode has lower contact resistance and charge transfer resistance between electrode and electrolyte than the pure α-Fe2O3 electrode. 3.0

1400 1st Charge 1st Discharge 10th Charge 10th Discharge 50th Charge 50th Discharge 100th Charge 100th Discharge 170th Charge 170th Discharge

1.5

90 80

1000

70

800

60 50

600

α-FC-300 Charge α-FC-300 Discharge α-Fe2O3 Charge

1.0

400 0.5

200

0.0 200

400

600

800

1000

1200

1400

0

100

Specific Capacity(mAh/g)

1400

(c)

1100

0.1C

900

0.2C

0.5C

1C

800

2C

700 600

20

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10

10

30

40

50

300

400

500

0 600

180 160 140 120 100 80 60 40 0.1C 20 0 -20 -40 -60 -80 -100 -120 60

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Specific capacity (mAh/g)

1200

1000

200

Charge Discharge Efficiency

1300

20

α-FC-300

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0

30

α-Fe2O3 Discharge

Cycle Number

0

40

Efficiency(%)

Voltage (V)

2.0

100 1200

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2.5

110

(b)

Efficiency(%)

(a)

Cycle Number

Fig.6. (a) Voltage profiles of the α-FC-300 electrode between 0.01 and 3.00 V at the current density of 0.1C, (b) Cycle performance of α-Fe2O3 and α-FC-300 hollow spheres at the current density of 1C,

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(c) Rate performance of α-FC-300 hollow spheres at different current density.

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ACCEPTED MANUSCRIPT 800 α[email protected] α-Fe2O3

Rs

RSEI

Rct

400

CPEd1

CPE2

W

200

0 50

100

150

Z' (ohm)

200

250

300

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0

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-Z'' (ohm)

600

Fig.7 EIS curves and typical equivalent circuit of the α-FC-300 and α-Fe2O3 electrodes without

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cycling.

4. Conclusion

The α-Fe2O3 hollow spheres were successfully synthesized via citric acid assisted hydrothermal

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synthetic method, and then the α-FC-300 hollow spheres can be obtained through annealing process with Ar after carbon coating. The superior electrochemical performance can be ascribed to the

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hollow structure and well-crystallized structure of the α-Fe2O3 spheres, as well as amorphous carbon layer, which can shorten the diffusion distance of both electrons and lithium ions, maintain structural

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integrity of the electrode during repeated lithiation process and improve the electronic conductivity of the anode materials. The synthesis process is simple, environment friendly and cost effective, which indicating the hollow α[email protected] spheres can be a potential candidate for high performance LIBs.

Acknowledgments

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ACCEPTED MANUSCRIPT The authors acknowledge the financial support from the National Natural Science Foundation of China (NSFC–No. 51202117), Natural Science Foundation of Beijing (No.2162037), the Beijing Nova

program

(Z171100001117077),

the

Beijing

outstanding

talent

program

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(No.2015000020124G121), the Fundamental Research Funds for the Central Universities (No.2014QJ02), and the State Key Laboratory of Coal Resources and Safe Mining (No.SKLCRSM16KFB04).

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ACCEPTED MANUSCRIPT [email protected] anodes for lithium-ion batteries, Appl Surf Sci, 390 (2016) 175-184. [28] S Chaudhari, M Srinivasan, 1D hollow α-Fe2O3 electrospun nanofibers as high performance anode material for lithium ion batteries, J Mater Chem, 22(2012) 23049-23056.

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ACCEPTED MANUSCRIPT Highlight The hollow α-Fe2O3 spheres was prepared via citric acid assisted hydrothermal method.



The α[email protected] hollow spheres deliver high reversible lithium storage capacity.



The α[email protected] hollow spheres exhibit superior rate performance.

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