C microspheres anode for lithium-ion batteries

C microspheres anode for lithium-ion batteries

Accepted Manuscript One-step Ultrasonic Spray Route for Rapid Preparation of Hollow Fe3O4/C Microspheres Anode for Lithium-ion Batteries Wen Deng, Suq...

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Accepted Manuscript One-step Ultrasonic Spray Route for Rapid Preparation of Hollow Fe3O4/C Microspheres Anode for Lithium-ion Batteries Wen Deng, Suqin Ci, Hao Li, Zhenhai Wen PII: DOI: Reference:

S1385-8947(17)31379-7 http://dx.doi.org/10.1016/j.cej.2017.08.039 CEJ 17490

To appear in:

Chemical Engineering Journal

Received Date: Revised Date: Accepted Date:

4 June 2017 8 August 2017 9 August 2017

Please cite this article as: W. Deng, S. Ci, H. Li, Z. Wen, One-step Ultrasonic Spray Route for Rapid Preparation of Hollow Fe3O4/C Microspheres Anode for Lithium-ion Batteries, Chemical Engineering Journal (2017), doi: http://dx.doi.org/10.1016/j.cej.2017.08.039

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One-step Ultrasonic Spray Route for Rapid Preparation of Hollow Fe3O4/C Microspheres Anode for Lithium-ion Batteries Wen Deng,1,2 Suqin Ci,1,* Hao Li,1,2 Zhenhai Wen1,2* 1 Key Laboratory of Jiangxi Province for Persistent Pollutants Control and Resources Recycle, Nanchang Hangkong University, Nanchang 330063, China 2 CAS Key Laboratory of Design and Assembly of Functional Nanostructures, Fujian Provincial Key Laboratory of Nanomaterials, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, P. R. China E-mail: [email protected]; [email protected] ABSTRACT: One-step preparation of nanoparticles-assembled hollow Fe3O4/C microsphere composites was achieved by an energy-efficient and continuous ultrasonic spray pyrolysis process. Systemically characterizations by scanning and transmission electron microscopy, X-ray diffraction, and Raman spectroscopy suggest that the physical and structure properties are highly dependent on the pyrolytic temperature; the outer surface of the hollow Fe3O4/C products are actually built by mesoporous carbon nanosheets overlaying Fe3O4 nanoparticles. Attributing to the synergistic effect of connected carbon layers and moderate hollow microsphere configuration with mesoporous nature, the optimal Fe3O4/C composites obtained at 800 °C deliver an initial specific discharge and charge capacity of 1236.0 and 1034.0 mAh g-1 with an initial coulombic efficiency of 83.65% at 0.1 A g-1, and the specific capacity can recover to above 1030 mAh g-1 after suffering 100 cycles when the current density was reduced from 4 to 0.1 A g-1. The present report may open up a promising opportunity to push forward application for next generation Li-ion batteries.

Keywords : Ultrasonic spray route, Iron oxide, Hollow microspheres, Anode, Lithium-ion batteries

Introduction Lithium-ion batteries (LIBs), because of their attracting features, including high energy and power densities and high cycle life, are currently dominating consumer market of energy storage devices for portable electronics and mobile electronic devices, and expectedly for power applications of electric vehicles and the grid in the near future [1-7]. Given that commercial graphite has already drawn near its theoretical limit of 372 mAh g−1 [8, 9], intensive effort has been devoted to seeking for next-generation LIBs anode materials to meet the ever-growing demand for high-performance power sources. Among numerous alternatives, iron-based oxide (e.g., Fe3O4) is one of the most promising anode materials for LIBs with featuring high theoretical capacity (926 mAh g-1), abundant raw material, low cost, and eco-friendly [10-21]. However, the rapid attenuation in capacity in Fe-based oxide, associated with poor cycling life, severely hinders its practical application owing to huge volume variation and poor electrical conductivity during the conversion reaction process [22-26]. Therefore, there still remain great challenges regarding how best to develop a viable, cost effective, facile fabrication strategy, in the hope that the as-designed Fe-based anode can potentially alleviate the huge volume change while attain a good electrical conductivity. To this end, there has been a veritable explosion of activity targeting to the development of high-performance Fe3O4-based anodes in the recent years, including various nanostructures (such as nanospheres [27, 28], nanosheets [29-32], nanofibers [33], nanorods [34, 35], nanonetworks [36]), Fe3O4-based hybrid nanocomposite [37-42] and functionalization of through coating [43-46] or doping [47-50]. In particular, conductive carbon engineered hollow or core-shell structured materials have been extensively studied, because the void spaces can provide space for buffering the volume variations while the carbon can ameliorate the conductivity [51-53]. Although great progress were made in the previous reports for improving the performance of Fe-based anodes for LIBs, further endeavors are still demanded in the exploration of a viable, cost effective, facile fabrication strategy to develop

high-performance Fe-based anode, catering to the requirements of the future’s LIBs market. Herein, we report a simple one-step, rapid and scalable spray pyrolysis method to prepare Fe3O4/C hollow microspheres composites that are built of carbon sheets supporting Fe3O4 nanoparticles. We demonstrate the products obtained at 800 °C, i.e., the Fe3O4/C-800, when studied as anode of LIBs, performed better than the other counterpart Fe3O4/C hollow microspheres, and was comparable to the best Fe3O4-based anode reported so far.

Experimental Section Chemical Reagents Iron(Ⅲ) chloride(FeCl3), ethylene glycol (EG) and citric acid monohydrate(CA) were purchased from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China). Iron chloride tetrahydrate (FeCl2·4H2O) was obtained from Tianjin Fuchen Chemical Reagents Factory (Tianjin, China). All the chemicals were of AR grade and used directly without further purification.

Synthesis of the nanoparticles-assembled Fe3O4/C composites The Fe3O4/C hollow microspheres were prepared by one-step ultrasonic spray pyrolysis. The schematic diagram of experimental device is shown in Fig. 1. Typically, nebulizer precursor was prepared by dissolving 4.0 g FeCl2·4H2O, 6.5 g FeCl3, 4.2 g CA, and 1.2mL EG in 500 mL deionized water with assistance of vigorously stirring. The mixed solution was aerosolized by using a 1.7 MHz ultrasonic nebulizer. The aerosol gas stream was carried into a 2-zone quartz reactor by carrier gas (high purity nitrogen) with a flow rate of 6 L min-1, during which the zone-1 tube was fixed at 300 °C and the zone-2 was tuned at 600 °C, 700 °C, 800 °C or 900 °C to collect a set of samples, denoted as Fe3O4/C-600, Fe3O4/C-700, Fe3O4/C-800 and Fe3O4/C-900, respectively. The whole preparation process occured very rapidly and the residence time of aerosol particles during spray pyrolysis was ~1 s.

Material characterization

The crystal structure and micro-structure of the products were studied by desktop X-ray diffraction (XRD, Mini Flex600, Rigaku), field emission scanning electron microscopy(FE-SEM, Nova NanoSEM450, FEI) and field emission transmission electron

microscope

(FE-TEM,

Tecnai

F20).

The

carbon content

of

the

carbon-wrapped Fe3O4 composites was determined by thermogravimetric analysis (TGA, STA449-F3, Netzsch) with a heating rate of 10 temperature to 800

/min from ambient

under air flow. The surface area and pore size distribution of the

powders were estimated by means of the Brunauere-Emmette-Teller (BET) method ( ASAP 2020, Micromeritics), using N2 as the adsorbate gas. Raman spectra were recorded

in

a

Microscopic

confocal

Raman

spectrometer

(Labram

HR

Evolution,Horiba Jobin Yvon) using 633 nm laser from an Ar+ laser source. X-ray photoelectron

spectroscopy

(XPS,

ESCALAB

250Xi,

ThermoFisher)

was

performed to study the chemical components in the surface of materials.

Electrochemical measurements The electrochemical performance of the samples was evaluated by fabricating a LIR2032 coin-type cell with Li metal as the counter electrode. Typically, the working electrode was manufactured as follow: 75 wt% of active material (Fe3O4/C hollow microsphere), 15 wt% of Super P (activated carbon) and 10 wt% of sodium carboxymethyl cellulose (CMC) were well mixed, a suitable amount of deionized water was gradually added in the mixture to form uniform slurry with assistance of grinding, then a thin layer of slurry was coated onto copper foil current collector (about 1.5 mg cm-2); the working electrode was obtained faster drying under vacuum at 120 °C for 20 h. For assembling half cell, micro-porous polypropylene film (Celgard 2400) was used as the separator and 1.0 M LiPF6 in a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) (1:1:1, v/v/v) was used as the electrolyte. The whole assembly process was conducted in an argon-filled glove box (LG2400/750TS-H, Vigor) with the moisture and oxygen content maintained below 0.5 ppm. The capacities and cycle performances of these half-cells were measured by a battery tester(Neware Technology LTD, China). Cyclic

voltammograms (CV) were recorded by an electrochemical analyser (CHI 604E) at a scanning rate of 0.1 mV s-1. The electrochemical impedance spectroscopy (EIS) was also performed by the same testing equipment instrument over the frequency range of 0.1MHz to 0.01Hz.

Results and discussion Fig. 1 depicts the set-up for synthesis of the Fe3O4/C hollow microsphere composites. The droplets produced in nebulizer were initially wafted into zone-1 tube (300 °C), Fe3O4 nanoparticles will be formed accompanying with adsorption of CA on their surface [23]. The aerogel were then passed through the zone-2 tube with a higher temperature, inducing a morphological evolution from fractal geometry to hollow microspheres composed of nanoparticles. The formation process for the Fe3O4/C hollow microsphere composites is schematically depicted in Fig. S1, which reveals different states of the nanoparticle assembly with temperature rise between the zone-2. We studied the representative SEM and TEM micrographs of the four products at low magnification (Fig. S2), confirming the morphology evolution from fractal powder (Fig. S2a and S2e), then hemisphere (Fig. S2b and S2f), and eventually to hollow microsphere (Fig. S2g and S2h) with increasing temperature. The morphology of microspheres change little when zone-2 tube was set at a temperature above 800 oC, as evidenced by the SEM images in Fig. S2c and S2d. But the Fe3O4/C-800 hollow microspheres are more well-distributed (Fig. 2a and 2b). The more detailed statistical distributions of the particle size of Fe3O4/C-800 are shown in Fig. 2c, revealing the size for the majority of the Fe3O4/C-800 is 0.5~1.5 µm in diameter. In order to further elucidate its structure, the Fe3O4/C-800 hollow microspheres were characterized in detail by TEM. Fig. S2g exhibits the typical TEM images

of

the

Fe3O4

hollow

microsphere,

evidently

illustrating

the

hollow microsphere structure with a thin layer of “gauze” on their surface. Fig. 2d-e show a magnified image of the single Fe3O4/C-800 hollow microsphere, demonstrating the thin surfaces on the hollow microsphere are actually made of

numerous nanoparticles. The high-resolution TEM images is displayed in the Fig. 2f, from which one can observe the nanoparticle, covered by a ultrathin layer of carbon with a thickness of ~1.25 nm, has a lattice spacing of 0.25 nm corresponding to the (311) planes of cubic phase Fe3O4. Fig. 2g presents the selected area electron diffraction (SAED) pattern of the single Fe3O4/C-800; the diffraction rings were ascribed to the (220), (311), (400), (422), (511) and (440) planes of the Fe3O4 [54]. XRD tests were conducted to clarify crystalline phase of the composites. Fig. S3 displays the XRD patterns of all the Fe3O4/C products from the pyrolysis temperatures at 600 , 700 , 800 not

significantly

and 900 . The peak positions and intensities for all samples do change

with

varying temperature,

suggesting

the

same

phase composition in the set of Fe3O4/C samples. As shown in Fig. 3a, the single Fe3O4/C-800 hollow microsphere shows diffraction peaks at 2θ values of 18.3o, 30.1o, 35.4o, 37.0o, 43.1o, 53.4o, 56.9o and 62.5 o, being well indexed to (111), (220), (311), (222), (400), (422), (511) and (440) of spinel-type cubic Fe3O4(JCPDS No. 19-0629). Although XRD patterns can not verify the presence of carbon layer, Raman spectra of the set of samples provide solid evidence (Fig. 3b).The Fe3O4/C-600 presents two humps that are amplified in the range of 1200-1800 (inset of Fig. 3b). By contrast, the Fe3O4/C-700, Fe3O4/C-800 and Fe3O4/C-900 clearly display D characteristic band for defects and disorders at ~1350 cm-1 and G characteristic band for typical graphite at ~1595 cm-1, which confirm existence of carbon. Moreover, the peak intensity ratio of two bands (ID/IG) is regard as a criterion to estimate the degree of disorder and graphitization of carbon material [55]. In general, the higher ID/IG values exhibit the higher degree of disorder. The ID/IG are 1.07, 0.941, 0.859 and 0.844 for Fe3O4/C-600, Fe3O4/C-700, Fe3O4/C-800 and Fe3O4/C-900, respectively, suggesting that the pyrolytic carbon is mainly in an amorphous structure and the carbon of as-obtained Fe3O4/C above 800 oC have relatively high orderliness and graphitizing grade [56]. Meanwhile, the Fe3O4/C-800 hollow microsphere manifests a mesoporous structure with a specific surface area of 53.17 m2 g-1, as detected by analysis of nitrogen isothermal adsorption/desorption and Brunauer-Emmett-Teller (BET) (Fig. 3c). And by comparing the Fig. S4, indicating that it has relatively high specific surface area.

In addition, thermogravimetric analysis (TGA, Fig. 3d) was used to estimate the carbon content. Considering that Fe3O4 will be changed into Fe2O3 upon heating in air, which

will

result

in

a

weight increment

of

about

3.45%

[57].

After analysis and calculation, the actual carbon content in various samples can be evaluated to be 10.14%, 16.23%, 21.16% and 24.63%, respectively (table in Fig. 3d). Surface states analysis was further carried out using X-ray photoelectron spectroscopy. Fig. 4a shows the survey XPS spectrum of the Fe3O4/C-800, where the photoelectron lines at binding energy of ~285, 530 and 712 eV are attributed to C1s, O1s and Fe2p [23], respectively, confirming the presence of C, O and Fe elements. Fig. 4b shows the high resolution XPS spectrum for Fe2p in the Fe3O4/C-800, which can deconvolute to Fe2p3/2 and Fe2p1/2 at 711.04 and 724.46 eV, respectively. And there appeared no shakeup satellite peak at 719.0 eV of Fe2O3 [58], suggesting the coexistence of dual iron oxidation state of Fe2+ and Fe3+ in Fe3O4/C-800 microspheres. According to Fig. 4c, there are three types of oxygen species may contribute to the O1s peak. From low to high is, the contribution of the anionic oxygen in Fe3O4 at about 530.2 eV, the oxygen containing functional groups at around 531.8 eV, and the oxygen in water at higher binding energies [59]. Fig. 4d exhibits the high resolution XPS spectra of C1s peak, the core level spectrum in the C1s region showed an asymmetric broad peak, which indicates presence of more than one chemical states of C [60] and the different types of functional groups on the surface. The C1s spectrum could be resolved into three peaks located at around 284.64 eV, 286.01 eV and 288.48 eV respectively, which are identified and assigned to the graphitized carbon (284.81 eV), O-C-O complex (286.1eV) and carboxyl/ester groups (288.48 eV), respectively [23, 49].

The lithium storage properties of Fe3O4/C composites were evaluated by using the Fe3O4/C as anodes in half-cell configuration. the typical cyclic voltammograms of the Fe3O4/C electrodes (Fig. 5a、 、 S5a、 、 S5c and S5e) are provided for the first three cycles in the voltage range of 0.01-3 V vs. Li/Li+ at a scan rate of 0.1 mV s-1. The initial cycle exhibits cathodic peaks at about 0.6, 0.9, 1.25 V and anodic peaks at 1.6,

1.84V, respectively; the two pairs of peaks correspond to the reduction reaction of Fe3O4 to Fe0 and Li2O and the formation of the solid electrolyte interface (SEI) layer caused by the irreversible decomposition of the electrolyte, as well as the oxidation process of Fe0 to Fe2+ and Fe3+ [57, 61]. It is noteworthy that, in subsequent cycles, the reduction and oxidation peaks are more and more coincident with the increase of reaction temperature, which indicates the formation of a stable SEI layer on the surfaces of hollow microspheres, thus maintaining the structural integrity of encapsulated Fe3O4/C during subsequent charge–discharge cycles, leading to satisfactory reversibility and electrochemical stability of host materials. These results are also supported by the galvanostatic discharge-charge of the as-prepared samples shown in Fig. 5b, Fig. S5b, Fig. S5d and Fig. S5f. The discharge-charge voltage profiles are in good agreement with their corresponding CVs, further confirming the typical electrochemical processes of Fe3O4. As seen in Fig. 5b, a voltage plateau can be observed at about 0.9 V in the first discharge, which then shifts to about 1.0 V and remains stable in the following cycles. In addition, a plateau at about 1.8 V in the charge process is identified. The initial discharge and charge capacities of the Fe3O4/C-800 are around 1236 and 1034 mAh g-1 at a current density of 100 mA g-1, respectively, corresponding to a rather higher initial coulombic efficiency of 83.65% than most of previous work (Table S1). Subsequently, the coulombic efficiency rapidly increases to over 95% after the first charge-discharge cycle. Fig. 5c exhibits rate performance of the set of Fe3O4/C composites electrodes, including Fe3O4/C-600, Fe3O4/C-700, Fe3O4/C-800 and Fe3O4/C-900, upon cycling in a step mode with different current densities ranging from 0.1 to 4.0 A g-1 with each ten cycles as a increment. As expected, the Fe3O4/C-800 delivers a capacity of about 1030 mAh g-1 at current density 0.1 A g-1, this value is significantly higher than the corresponding capacity of the Fe3O4/C-600 (600 mAh g-1), the Fe3O4/C-700 (760 mAh g-1) and the Fe3O4/C-900 (730 mAh g-1). Note that this reversible capacity of Fe3O4/C-800 is higher than the theoretical value of 926 mAh g-1. In general, Such a high capacity is considered to be associated with the interfacial Li storage by a pseudo-capacitive mechanism or formation of a polymer/gel-like layer on electrode

surface.[45] Interestingly, the initial discharge capacity of Fe3O4/C-700 can reach to a high value of 1558 mAh g-1, showing the highest initial discharge capacity in all Fe3O4/C composites, but only deliver a specific capacity of about 820 mAh g-1 (52.6 % of the initial capacity) with notable fading after first few discharge-charge cycles. The existence of incomplete hollow sphere with abundant cavernous space may provide plenty of interaction interface for discharge process of reduction reaction, as evidenced by a relative higher BET surface area (73.14 m2 g-1) in Fe3O4/C-700 (Fig. S4), but the disintegrate fragile framework readily pulverize electrode material, thus resulting the rapid decline of specific capacity in the following cycles. Remarkably, even at a high rate of 4.0 A g-1, the Fe3O4/C-800 hollow spheres could still achieve a discharge capacity of as high as 370 mAh g-1, which is almost as high as the theoretical capacity of commercial graphite (372 mAh g 1) after 50 cycles at the −

current density stepwise increasing from 0.1 to 4.0 A g-1. Moreover, specific capacity can recover to above 1030 mAh g-1 and possess better stability suffering 100 cycles when the current density was reduced from 4 to 0.1 A g-1 again, demonstrating that Fe3O4/C-800 exhibits the outstanding rate property. In addition to impressive rate performance, the Fe3O4/C electrodes also exhibit excellent reversible capacity and cycling stability. Fig. 5d shows the cycle performances of the Fe3O4/C composites at a fixed current density of 1.0 A g-1. Obviously, the Fe3O4/C-800 shows much better cyclic capacity retention than the Fe3O4/C-600, the Fe3O4/C-700 and the Fe3O4/C-900, with a high reversible capacity of about 600 mA h g-1 retained after 200 cycles compared to about 170, 250 and 317 mAh g-1 for Fe3O4/C-600, Fe3O4/C-700 and Fe3O4/C-900 respectively. On the other hand, for evaluating the long cycling performance of the Fe3O4/C-800, the long-term cycling behavior is shown in Fig. 5e, which was investigated at 2.0 A/g. The initial discharge and charge capacities of the electrode are 637 and 585 mAh g-1 respectively, showing a very high initial coulomb efficiency of 91.8% (inset of Fig. 5e). And the coulomb efficiency of the electrode increases to around 98 % during the first ten cycles, after which high coulomb efficiency of above 98 % are maintained. After 500 cycles, the electrode still shows a high discharge capacity of 392 mAh g-1. In order to

further understand the electrochemical behaviors, the electrochemical impedance spectroscopy (EIS) was studied on the four Fe3O4/C materials after 3 charging/discharging cycles (Fig. 6). All Nyquist plots are composed of one semicircle in high-medium frequency region and a linear tails in low frequency region; which are relative to the charge-transfer impedance and the Warburg impedance of the Li+ diffusion in the solid materials, respectively [28, 62]. From the inset of Fig. 6, the diameter of the semicircle for Fe3O4/C-800 electrodes (~ 82 Ohm) is manifestly smaller than those of the other three electrodes, indicating lowest charge-transfer resistances among the Fe3O4/C electrodes. The morphologyical and structural changes of electrode materials in the fully delithiated state after 200 cycles at a current density of 1 A g-1 were examined by TEM (Fig. S6a-S6d). it is clear that morphology of all the active materials except Fe3O4/C-800 is seriously damage. Moreover, TEM image of Fe3O4/C-800 after 500 cycles at a current density of 2 A g-1 is also shown in Fig. S6e, which confirms presence of microspheres morphology. This is indicates that the agglomeration and pulverization of Fe3O4/C microspheres were effectively suppressed. Above microscopic structural characterizations further demonstrate the excellent structural stability of the Fe3O4/C-800 anode during cycling, which plays a crucial role in improving lithium-storage capability. The above results evidently demonstrate the following points: i) Although the phase of all the product doesn't change, from microtopography analysis the Fe3O4/C-800 composites possess a stronger assembly structure than the other three, which could offer enough space to best circumvent the severe volume contraction/expansion associated with charge-discharge process; ii) TGA and Raman spectra show that all the samples contain conductive carbon, however, result of the minimum ID/IG value suggests

that

carbon

frameworks

of

Fe3O4/C-800

have

a

higher

degree of graphitization, which effectively enhance the electrical conductivity and also regarded as a protective layer for preventing the deformation of hollow sphere; iii) Mesoporous feature of Fe3O4/C-800 renders the composite with excellent ionic conductivity, thereby facilitating to an efficient lithium electrochemical utilization and

fast reaction kinetics. For these reason, the Fe3O4/C-800 hollow microsphere composites exhibit the optimal electrochemical characteristic with superior rate capability as well as good cycling stability. Moreover, the Fe3O4/C-800 also show advantages in term of electrochemical performance over the Fe3O4/C composite anode reported previously (Table S1).

Conclusions In summary, the Fe3O4/C hollow microsphere composites were reported as the anode of lithium ion batteries with high capacity and high rate capability, which were synthesized via a one-step ultrasonic spray pyrolysis process without post-heat treatment. our strategy of controlling the pyrolysis temperature offers one degree of freedom, enabling morphology of hollow sphere with porous nature of as-grown Fe3O4 nonaparticles in a droplet to be tuned, and can also be used to inquire the process parameters of simple and efficient to achieve high reversible capacity, highlighted initial coulomb efficiency and considerable capacity retention. At a high reaction temperature of 800 oC, the Fe3O4/C composites with mesoporous feature shows higher reversible capacity, highlighted initial coulomb efficiency and better rate performance, owing to the synergistic effect of connected carbon layers and moderate hollow microsphere configuration with mesoporous nature, which allows for fast lithium ion diffusion and effectively eases volume expansion during high-rate long charge/discharge cycles and sustain the integrity of the electrode structure during lithium insertion/extraction process. The present work provide us with a simple method to rapid preparation of hollow microsphere products with coating carbon assembled by small primary particle size, which is suitable for cost-effective and large-scale production. It is of great significance to generalize this strategy to the preparation

of

other

transition

metal

compounds/carbon

composites

with

high-performance and environment-friendly for next generation energy-storage devices and the smart grid.

Acknowledgements This work was supported by the National Natural Science foundation of China (21566025), Aeronautical Science Foundation of China (2015ZF56017), the Science Fund of Jiangxi Province for Distinguished Young Scholars (20162BCB23044), and the Natural Science Foundation of Jiangxi Province (20152ACB21019). Z. H. W. is also thankful for the award of“The Recruitment Program of Global Youth Experts” and Hundred Talents Program of Fujian Province.

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Fig. 1. Schematic diagram of the ultrasonic spray pyrolysis applied in the preparation of the carbon-wrapped Fe3O4 hollow microspheres.

a

200

b

c

quantity

d

e

f

g

60.0%

56.1%

proportion

160

40.0% 120

175

80 40 0

18.3% 6.4% 20

9.0% 28

57

20.0%

8.6% 27

1.6% 5

0.0%

Fig. 2. Morphologies of the Fe3O4/C-800 hollow microsphere: (a, b) SEM images, (c) statistical distribution of particle diameter in Fe3O4/C-800, (d, e) TEM images, (f) HRTEM image and (g) SAED pattern.

120

Intensity(a.u)

Fe3O4/C800 (220)

(400) (222)

(111)

(440) (511) (422)

JCPDS No.19-0629

0.03

100 80

Fe3O4/C-800

-1

140 3

(c)

dV/dlogD(cm g )

(311)

Quantity(cm 3 g-1 )

(a)

60

0.02 0.01 0.00 0

40

10 20 30 Pore Diameter(nm)

20

40

BET surface area: 53.17m2 g-1

0 15

25

35

45

55

0.0

65

0.2

(b)

Weight Loss( %)

intensity( a.u.)

Fe3O4-900

Fe3O4-800 Fe3O4-700 1200

1500

0.6

0.8

1.0

(d) 100

G D

Fe3O4-600

0.4

Pressure(P/P0)

2 theta(deg)

1800

800 950 1100 1250 1400 1550 1700 1850 2000 -1

Raman Shift(cm )

95 Fe3O4/C-900

90

Fe3O4/C-800

85 symbol weight loss

10.14% 16.23% 21.16% 24.63%

80 75 70 0

200

Fe3O4/C-700 Fe3O4/C-600

400

600

Temperature( ℃)

800

Fig. 3. (a) XRD pattern and (b) N2 adsorption-desorption isotherms and Pore size distribution (inset) of the Fe3O4/C-800; (c) Raman spectra and (d) TGA curves of Fe3O4/C composites prepared at different temperatures.

c Fe2p

200

310

420

530

640

750

526

Binding Energy( eV)

b Fe2p3/2

712

Intensity(a.u.)

Fe2p1/2

719

726

733

Binding Energy( eV)

528

530

532

534

536

Binding Energy( eV)

Intensity(a.u.) 705

O1s

Intensity(a.u.)

O1s

C1s

Intensity(a.u.)

a

740

d

280

C1s

285

290

295

Binding Energy( eV)

Fig. 4. XPS spectra of Fe3O4/C-800: (a) survey spectrum, high resolution spectrum for (b) Fe2p, (c) O1s, and (d) C1s.

0.2

(b) 3.0

0.0

2.4

Voltage(V)

Current (mA)

(a)

-0.2 -0.4

1st cycle 2nd cycle 3rd cycle

-0.6 -0.8

1.8 1.2 0.6 0.0

-1.0 0.5

1.0

1500

2.0

2.5

1200 0.1A g-1

-1

3.0

600-Discharge-Charge 700-Discharge-Charge 800-Discharge-Charge 900-Discharge-Charge 0.1A g-1

-1

2A g-1

g

600 300

Capacity(mAh·g )

900 800 700 600

1000 800 600 400 200 0

0

(e)

200 400 600 800 1000-1 1200 1400 1600

1200

0.2A g 0.5A g-1 -1 1A g

900

0

(d)

+

4A

-1

Capacity/(mAh· g )

1.5

Voltage (V) vs. Li/Li

C apacity(m A h g -1 )

0.0

(c)

1st 2nd 3rd

0

10 20 30 40 50 60 70 80 90 100

0

25

50

75

Cycle number

100

125

150

175

200

Cycle number

1600

1200 1000 800

3.0 2.5 2.0 1.5 1.0 0.5 0.0

-1

2A g

Fe O /C-800 discharge 3

ICE=91.8% 0

600

4

80

Fe O /C-800 charge 3

150 300 450 600 750 -1 Capacity(mAh g )

4

coulombic efficency

60

400 200

Coulombic effciency(%)

100 Voltage(V)

-1

Capacity(mAh· g )

1400

40 0 0

100

200

300

400

500

Cycle number

Fig. 5. (a) CV curves and (b) galvanostatic discharge/charge curves of the Fe3O4/C-800 vs. Li/Li+; (c) rate performance at different current densities and (d) the cycling performance at 1A/g of Fe3O4/C-600, Fe3O4/C-700, Fe3O4/C-800 and Fe3O4/C-900; (e) the long cycling performance and the first cycle discharge -charge curve (inset) at a current density of 2.0A/g of Fe3O4/C-800.

1000 600 700 800 900

-z''/ohm

800 600 400 200

50 100 150 200 250

0 0

200

400

600

800

1000

Z'/ohm Fig. 6. EIS plots of four active materials after 3 cycles and inset is the partial enlarged detail.

Supporting Information for: One-step Ultrasonic Spray Route for Rapid Preparation of Hollow Fe3O4/C Microspheres Anode for Lithium-ion Batteries Wen Deng,1,2 Suqin Ci, * Hao Li, Zhenhai Wen1,2* 1,

1,2

1 Key Laboratory of Jiangxi Province for Persistent Pollutants Control and Resources Recycle, Nanchang Hangkong University, Nanchang 330063, China 2 CAS Key Laboratory of Design and Assembly of Functional Nanostructures, Fujian Provincial Key Laboratory of Nanomaterials, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, P. R. China E-mail: [email protected]; [email protected]

Fig.S1 Schematic diagram for the formation of nanoparticles-assembled Fe3O4/C composites.

a

e

b

f

c

g

d

h

Fig.S2 Low range SEM (left) and TEM (right) images of products prepared at different temperatures: (a, e) Fe3O4/C-600, (b, f) Fe3O4/C-700, (c, g) Fe3O4/C-800 and (d, h) Fe3O4/C-900.

Fe3O4/C-900

Intensity(a.u)

Fe3O4/C-800

Fe3O4/C-700

Fe3O4/C-600

10

20

30

40

50

60

70

80

2 theta (deg) Fig. S3. XRD patterns of Fe3O4/C-600, Fe3O4/C-700, Fe3O4/C-800 and Fe3O4/C-900.

Fe3O4/C-600 0.18

3

-1

dV/dlogD(cm g )

3 -1 Quantity(cm g )

176

132 88

0.12 0.06 0.00

44

0

5 10 15 20 25 Pore Diameter(nm) 2

0 0.0

0.2

0.4

0.6

0.06

1.0

Fe3O4/C-700

3

-1

dV/dlogD(cm g )

3 -1 Quantity(cm g )

60

0.8

Pressure(P/P0)

100 80

-1

BET surface area: 42.31m g

0.04 0.02 0.00

40

0

2 4 6 8 10 12 Pore Diameter(nm)

20

BET surface area: 73.14m2/g

0 0.0

0.2

0.4

0.6

0.8

1.0

Pressure(P/P0)

Quantity(cm3 g-1)

60 40

-1

Fe3O4/C-900

0.012

3

80

dV/dlogD(cm g )

100

0.008 0.004 0.000 0

5 10 15 20 25 Pore Diameter(nm)

20 2 -1

BET surface area: 47.00m g

0 0.0

0.2

0.4

0.6

0.8

1.0

Pressure(P/P0) Fig. S4. N2 adsorption- desorption isotherms and inset of pore size distribution of (a) the Fe3O4/C-600, (b) the Fe3O4/C-700 and (c) the Fe3O4/C-900.

0.2

b

Fe3O4/C-600

-0.4 -0.6

1st cycle 2nd cycle 3th cycle

-0.8 -1.0 0.0

1.0

1.5

2.0

2.0 1.5 1.0

0

3.0

-0.3

2.0

-0.6

1st cycle 2nd cycle 3rd cycle

-0.9

1.0

1.5

2.0

2.5 +

0.2

0

2.0

-0.8 -1.0 0.0

0.5

1.0

1.5

2.0

2.5

+

Voltage(V) vs. Li/Li

3.0

250 500 750 1000 1250 1500 1750 2000 -1 Capacity(mAh·g )

3.0

-0.2

1st cycle 2nd cycle 3rd cycle

Fe3O4/C-700

0.0

2.5

-0.6

900 1050

1.0

0.0

-0.4

750

1st 2nd 3rd

0.5

f

Fe3O4/C-900

600

1.5

3.0

Voltage(V) vs.Li/Li

450

-1

2.5

e

300

Capacity(mAh·g )

0.0

0.5

150

d

Fe3O4/C-700

0.0

Fe3O4/C-600

0.0

3.0

Voltage(V) vs.Li/Li

-1.2

Current (mA)

2.5 +

0.3

1st 2nd 3rd

0.5

Voltage(V)

Current(mA)

0.5

Voltage(V)

-0.2

c

3.0 2.5

0.0

Voltage(V)

Current (mA)

a

1st 2nd 3rd

1.5 1.0 0.5

Fe3O4/C-900

0.0 0

200

400

600 800 1000 1200 1400 -1 Capacity(mAh·g )

Fig. S5. GCD curves (left) and CV curves (right) of (a, b) Fe3O4/C-600, (c, d) Fe3O4/C-700 and (e, f) Fe3O4/C-900 vs. Li/Li+, respectively.

Fig. S6. Typical fully charged TEM images after 200 cycles at a current density of 1 A g -1: (a) Fe3O4/C-600, (b) Fe3O4/C-700, (c) Fe3O4/C-800 and (d) Fe3O4/C-900. (e) TEM image of a fully charged Fe3O4/C-800 after 500 cycles at a current density of 2 A g -1.

Table S1 Comparisons between the nanoparticles-assembled Fe3O4/C composites and previously reported Typical materials

Synthesis

Fe3O4/C hollow microsphere

one-step spray pyrolysis

ICE(initial discharge/ charge) [mAh g-1 ] 83.65% (1236/ 1034)

Current density (A g−1)

0.1

Electrochemical performance

Ref.

1035 mAh g-1 after 100 cycles at 100 mA g-1

this work

430 mAh g-1 after 100 cycles

S1

method

Fe3O4/C composites [email protected] composites [email protected] core–shell nanorings Fe3O4/rGO composite Fe3O4/Fe/ MWCNT nanocomposites urchin-like [email protected] Fe3O4 nanorod/N-doped GN C-Fe3O4 nanospheres

ball milling method CVD method

67.8% (712/483)

~70%

0.1

synchronous

70.6% (1295.6/914.7)

0.1

77.5% (1090/845)

0.5

60.4% (910/550)

0.168

method

73.3% 1185/925

0.5

hydrothermal method

~67% (~1190/~800)

0.1

solvothermal

76.6% (1166/893)

-

reduction method hydrogen plasma method electrical wire pulse method hydrothermal

method solvothermal

Fe3O4 @GS/GF

method

Ni foil-supported interconnected Fe3O4 nanosheets

chemical bath deposition method

~79% (~1340/~1060)

77% (1045/806)

-

0.093

0.1

550 mAh g-1 after 60 cycles at 100 mA g-1 923 mAh g-1 after 160 cycles at 200 mA g-1 890 mAh g-1 after 100 cycles at 500 mA g-1 460 mAh g-1 after 50 cycles at 168 mA g-1 800 mAh g-1 after 100 cycles at 500 mA g-1 929 mAh g-1 after 70 cycles at 100 mA g-1 712 mAh g-1 after 60 cycles 1059 mAh g-1 after 150 cycles at 93 mA g-1 690 mAh g-1 after 100 cycles at 100 mA g-1

S2

S3

S4

S5

S6

S7

25

26

28

Fe3O4/C nanosheets

solvothermal and annealing

Core-shell [email protected] nanospheres yolk-shell [email protected]@N-d oped carbon

solvothermal

~60% (~1290/~780)

0.05

80% (~1130/~904)

0.3

~62% (~1330/~830)

0.2

method

Fe3O4−TiO2− Carbon Composite

method SiO2 template method

surface 45.8% sol−gel (1340.4/613.8) method cold 70.8% [email protected] quenching (1305.9/925.1) method (The initial coulombic efficiency=ICE)

0.1

0.1

647 mAh g-1 after 100 cycles at 100 mA g-1 841 mAh g-1 after 60 cycles at 100 mA g-1 500 mAh g-1 after 500 cycles at 2000 mA g-1 525 mAh g-1 after 100 cycles at 100 mA g-1 1113.5 mAh g-1 after 50 cycles at 100 mA g-1

29

33

35

42

44

References [S1] P. Wang, M. Gao, H. Pan, J. Zhang, C. Liang, J. Wang, P. Zhou, Y. Liu, A facile synthesis of Fe3O4/C composite with high cycle stability as anode material for lithium-ion batteries, Journal of Power Sources, 239 (2013) 466-474. [S2] J. Wang, M. Gao, D. Wang, X. Li, Y. Dou, Y. Liu, H. Pan, Chemical vapor deposition prepared bi-morphological carbon-coated Fe3O4 composites as anode materials for lithium-ion batteries, Journal of Power Sources, 282 (2015) 257-264. [S3] L. Wang, J. Liang, Y. Zhu, T. Mei, X. Zhang, Q. Yang, Y. Qian, Synthesis of [email protected] core-shell nanorings and their enhanced electrochemical performance for lithium-ion batteries, Nanoscale, 5 (2013) 3627-3631. [S4] Q. Zhou, Z. Zhao, Z. Wang, Y. Dong, X. Wang, Y. Gogotsi, J. Qiu, Low temperature plasma synthesis of mesoporous Fe3O4 nanorods grafted on reduced graphene oxide for high performance lithium storage, Nanoscale, 6 (2014) 2286-2291. [S5] D.-H. Lee, S.-D. Seo, G.-H. Lee, H.-S. Hong, D.-W. Kim, One-pot synthesis of Fe3O4/Fe/MWCNT nanocomposites via electrical wire pulse for Li ion battery electrodes, Journal of Alloys and Compounds, 606 (2014) 204-207. [S6] S.M. Yuan, J.X. Li, L.T. Yang, L.W. Su, L. Liu, Z. Zhou, Preparation and lithium storage performances of mesoporous [email protected] microcapsules, ACS applied materials & interfaces, 3 (2011) 705-709. [S7] J.S. Xu, Y.J. Zhu, Monodisperse Fe3O4 and gamma-Fe2O3 magnetic mesoporous microspheres as anode materials for lithium-ion batteries, ACS applied materials & interfaces, 4 (2012) 4752-4757.

Highlights One-step rapid preparation; Hollow Fe3O4/C Microspheres Anode; A high-performance lithium ions batteries anode