Facile Fabrication of Honeycomb-like Carbon Network-Encapsulated

Subscriber access provided by UNIV OF DURHAM

Energy, Environmental, and Catalysis Applications

Facile Fabrication of Honeycomb-Like Carbon Network Encapsulated Fe/Fe3C/Fe3O4 with Enhanced Li-Storage Performance Can Guo, Jiapeng He, Xinyi Wu, Qingwen Huang, Qingpeng Wang, Xinsheng Zhao, and Qinghong Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b13331 • Publication Date (Web): 28 Sep 2018 Downloaded from http://pubs.acs.org on October 1, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Facile Fabrication of Honeycomb-Like Carbon Network Encapsulated Fe/Fe3C/Fe3O4 with Enhanced Li-Storage Performance Can Guo†, Jiapeng He†, Xinyi Wu†, Qingwen Huang†, Qingpeng Wang‡, Xinsheng Zhao*§, and Qinghong Wang*† †

School of Chemistry and Materials Science, Jiangsu Key Laboratory of Green Synthetic

Chemistry for Functional Materials, Jiangsu Normal University, Xuzhou, Jiangsu 221116, China ‡

§

Institute of Biopharmaceutical Research, Liaocheng University, Liaocheng 252059, China Hydrogen Research Lab for Energy Storage and Application, School of Physics and Electronic

Engineering, Jiangsu Normal University, Xuzhou 221116, China * Corresponding authors: Qinghong Wang: [email protected] Xinsheng Zhao: [email protected] KEYWORDS: Honeycomb-like carbon networks; Fe/Fe3C/Fe3O4 composite; Pyrolysis process; Lithium ion batteries; Electrochemical performance

ACS Paragon Plus Environment

1

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 22

ABSTRACT: Three-dimensional honeycomb-like carbon network encapsulated Fe/Fe3C/Fe3O4 composites are constructed via a facile pyrolysis of ferrite nitrate-PVP precursors. The nanostructures of the composites form in terms of the iron catalysis in the pyrolysis process, which greatly depends on reaction temperature and contents of raw materials. The Fe/Fe3C/Fe3O4/C composite obtained at 700 0C possesses high surface area, outstanding structural stability and fast electron/Li ion transportability. As anode for lithium-ion batteries, it displays high specific capacity (1295 mAh g-1 at 0.2 A g-1), long cycling stability and fast kinetics (345 mAh g-1 after 500 cycles at 5 A g-1). Besides the nanostructures, the marriage of different components also contributes to the superior electrochemical performance. The integral carbon matrix supplies fast electron/Li transportation pathway. Fe/Fe3C acts as electrocatalysts in the electrode, which may bring extra capacity. The satisfied performance and facile fabrication with low cost make it a competitive material in practical applications.

1. INTRODUCTION Lithium ion batteries (LIBs) have become dominant in energy storage devices owing to the advantages of high energy density, superior cycling performance and low pollution.1-4 However, the fast growing demand for high-rate and high-capacity LIBs results in urgent development of advanced electrode materials.5-8 Graphite has been commercially used because of its low cost, long cycle life and good conductivity. However, the low specific capacity (theoretical capacity is only 372 mAh g-1) and poor rate performance seriously limit its further application in LIBs. As anode for LIBs, iron oxides display advantages of high theoretical capacities (924 mAh g-1 for Fe3O4, 1005 mAh g-1 for Fe2O3), low cost, non-toxicity and natural abundance.9-13 However, the intrinsic poor conductivity results in slow kinetics and poor rate performance. Moreover, the serious volume change during the cycling process causes the pulverization of electrode, resulting


2

Page 3 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


in a severe capacity fading.14-16 To solve these problems, researchers have developed many effective strategies, among which carbon decoration is commonly employed.17, 18 For example, Fe3O4-CNTs composites,19 Fe3O4/mesoporous carbon spheres20 and Fe2O3-CNTs-graphene hybrids21 exhibit high specific capacities and enhanced cycling stability. It is demonstrated that the 3D carbon matrix possesses the merits of stable integral networks, high porosity and excellent conductivity, endowing the electrode with fast electron/ion transportability and good cycling stability.22-24 For example, Li et al. fabricated the 3D net-like FeOx/C composite and obtained high charge capacity (851.3 mAh g-1 after 50 cycles at 0.2 A g-1).25 In our previous research, 3D carbon networks were constructed by an in-situ strategy and endowed FeS with outstanding sodium storage performances.26 Besides iron oxides, metal iron and iron carbides also attract much interest. Based on the conversion mechanism, Fe and Fe3C are inactive for Li storage. This is because Fe is electrochemically inert to Li, and each unit of Fe3C stores only 1/6 Li (~26 mAh g-1). But Su et al. found that Fe and Ni nanoparticles (NPs) and Fe3C can serve as electrocatalysts for the reversible formation/decomposition of some components in solid electrolyte interface films, thus bringing extra capacity.27-29 Moreover, Fe3C nanomaterials exhibit good chemical stability and excellent mechanical strength. As coating layer, it can effectively buffer the radical volume change of active materials.30 A series of Fe@Fe3C/C28, 31 and Fe2O3/Fe3C/C composites32, 33 have been reported to display high discharge capacity and excellent rate performance. Herein, a marriage of Fe3O4 active materials, Fe/Fe3C electrocatalysts and 3D carbon networks is realized via a facile in-situ synthesis method by ion catalysis. Alternatively, such an unique honeycomb-like carbon network encapsulated Fe/Fe3C/Fe3O4 structure reveals the merits: 1) uniform encapsulation of Fe/Fe3C/Fe3O4 NPs in carbon matrix provides abundant electrochemical


3


Page 4 of 22

reaction sites and relieves the volume expansion of active materials in charge-discharge reactions; 2) integral honeycomb-like carbon networks offer interconnect paths for fast ion diffusion and electron migration; 3) the electrocatalytic effect arising from Fe/Fe3C NPs may boost the overall performance. Such a synergistic effect makes the as-prepared Fe/Fe3C/Fe3O4/C composite show desirable lithium storage properties. 2. EXPERIMENTAL SECTION 2.1. Synthesis Synthesis of FeOx/C-1.8-700 composites. 3D honeycomb-like carbon network encapsulated Fe/Fe3C/Fe3O4 composites were prepared via a facile Sol-gel method, followed by a pyrolysis process. In a typical synthesis, 30 mL of deionized water, 1.8 g of Fe(NO3)3∙9H2Oand 1.0 g of polyvinyl pyrrolidone (PVP K30) were mixed and stirred in a water bath at 80 0C for 3h to form wet gel. Then it was dried under vacuum at 60 0C to form dark brown precursor gel. Finally, the precursor was heated to 700 0C under flowing Ar atmosphere with an increasing rate of 2 0C min1

at. After heated for 1 hour the FeOx/C-1.8-700 composite was achieved. In addition, the effects of ferric nitrate content (1.5, 1.8 and 2.1 g) and annealing temperature

(600 0C, 700 0C and 800 0C) on the structures and morphologies of the products were also investigated, and the products are denoted as FeOx/C-1.5-700, FeOx/C-1.8-700, FeOx/C-2.1-700, FeOx/C-1.8-600 and FeOx/C-1.8-800, respectively. 2.2 Materials characterization and electrochemical measurements The as-prepared FeOx/C composites are investigated as anode materials for LIBs. The methods of materials characterization and electrochemical measurements are similar to our previous report.26 Details can be seen in electronic supporting information. 3. RESULTS AND DISCUSSION


4

Page 5 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3.1. Material characterization and probable formation mechanism The 3D honeycomb-like carbon network decorated with Fe/Fe3C/Fe3O4 nanoparticles was fabricated by a two-step process. As shown in Scheme 1, the first step involves a simple sol-gel process to prepare Fe-PVP coordination complex dry gel precursor. In the next step, the gel precursor was ground and annealed under Ar atmosphere, thus yielding the carbon-encapsulated Fe/Fe3C/Fe3O4 composite. The formation of the Fe/Fe3C/Fe3O4 embedded honeycomb-like carbon nanostructure is based on the in-situ metal-ion (Fe3+) catalytic graphitization effect. The adhesive feature of PVP and the chelation effect between PVP and Fe3+ make the gel precursor possess an integral microstructure with homo-dispersion of Fe3+.34 During the following pyrolysis process, the removal of CO2 and H2O benefits the generation of the porous structure. Moreover, Fe3+ are employed as catalysts to induce the graphitic of carbon, leading to the rearrangement of graphitic carbon into honeycomb-like nanostructure.35 Meanwhile, Fe3+ converses into Fe3O4, Fe3C or Fe due to the reduction and carbonization of carbon, totally encapsulated in the carbon matrix.32 Scheme 1. Schematic illustration of honeycomb-like carbon network encapsulated Fe/Fe3C/Fe3O4 composite synthesis.

It is noticed that the annealing temperature is a key factor influencing the phases and morphologies of the products. As shown in Figure 1a, when the temperature is 600 0C, the X-ray


5


Page 6 of 22

diffraction (XRD) pattern of FeOx/C-1.8-600 matches well with Fe3O4 (JCPDS No 88-315) and metal Fe (JCPDS No 87-722). When the temperature is increased to 700 0C and 800 0C, the main phases of FeOx/C-1.8-700 and FeOx/C-1.8-800 are both Fe3C (JCPDS No 72-1110), while Fe and Fe3O4 are not obviously observed. It is clear that Fe/Fe3O4 composite is formed at 600 0C and then tend to transform into Fe3C while increasing the temperature.

Figure 1. (a) XRD patterns and (b) XPS spectrum of the as-prepared FeOx/C composites. Highresolution (c) Fe 2p and (d) C 1s XPS spectra of FeOx/C-1.8-600. High-resolution (e) Fe 2p and (f) C 1s XPS spectra of FeOx/C-1.8-700. High-resolution (g) Fe 2p and (h) C 1s XPS spectra of FeOx/C-1.8-800.


6

Page 7 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


To further confirm the chemical composition of the composite, X-ray photoelectron spectroscopy (XPS) was carried out. The survey XPS (Figure 1b) confirms the presence of Fe, O, C, and N in all the samples. The trace element N derives from the thermal decomposition of PVP. The high-resolution XPS spectrum of Fe in FeOx/C-1.8-600 (Figure 1c) exhibits three peaks at 723.5, 709.9 and 706.5 eV, belonging to Fe 2p1/2 and Fe 2p3/2 in Fe3O4, and Fe 2p3/2 in Fe/Fe3C, respectively. After fitted with Casaxps software, the peaks at 712.1 and 725.3 eV can be assigned to Fe 2p3/2 and Fe 2p1/2 of Fe3+ in Fe3O4, while for those located at 710.2 and 723.4 eV it can be attributed to Fe 2p3/2 and Fe 2p1/2 of Fe2+ in Fe3O4, respectively.36 The peaks appearing at 708.2 and 706.5 eV are indexed to Fe 2p3/2 in metal Fe3C and Fe, respectively.37 For the peak located at 718.9 eV, it belongs to a satellite peak. The sub-XPS spectrum for C 1s peaks (Figure 1d) can be divided into three peaks at 284.6, 285.1 and 283.5, corresponding to sp2 C-C and sp3 C=C bonding in carbon matrix, and C-Fe bonding in Fe3C. From these peaks it can be confirmed that FeOx/C1.8-600 is a mixture of Fe3O4, Fe, Fe3C and N-doped C. Due to the trace of Fe3C, it is hardly observed from the XRD analysis. Comparing the sub-XPS spectrum for Fe 2p in FeOx/C-1.8-600, FeOx/C-1.8-700 and FeOx/C-1.8-800, it is revealed that the relative intensity of the peaks of Fe and Fe3C increases, while those for Fe3O4 decreases when the temperature increases. From the subXPS spectrum for C, it is obvious that Fe-C bonding increases from 600 to 800 0C. It is inferred that the main phase transformation process could be that Fe3O4 phase was firstly produced and then reduced to Fe by carbon precursor, and finally transforms to Fe3C. The conversion proceeds more and more thorough with the increase of temperature. The morphologies of FeOx/C-1.8-600, FeOx/C-1.8-700 and FeOx/C-1.8-800 were characterized by field-emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM). FeOx/C-1.8-700 presents a porous 3D honeycomb-like nanostructure, which is composed


7


Page 8 of 22

of interconnected carbon nanosheets (Figure 2a). From the TEM image (Figure 2b), it can be seen that each nanosheet is embedded with homogeneously dispersed nanoparticles about 20 nm in diameter. Obviously, each nanoparticle presents typical core-shell structure, with the shell thickness of 3~4 nm (Figure 2c and 2d). To further clarify the interfaces between scattered nanoparticles and carbon matrix, scanning transmission electron microscopy (STEM) observations of FeOx/C-1.8-700 were conducted. As shown in Figure 2e, in the core, it displays two typical dspacing of 0.132 and 0.168 nm, attributed to (123) and (230) crystal planes of Fe3C, respectively. While in the shell, it shows clear lattice fringes with typical d-spacing of 0.209 and 0.250 nm, corresponding to crystal planes (110) and (211) of Fe and Fe3O4 phases. As can be seen that individual nanoparticle is wrapped and connected by graphitic carbon with a characteristic dspacing value of C (002) planes (0.340 nm). The energy dispersive spectral (EDS) element mapping of FeOx/C-1.8-700 displays the distribution of Fe, O and C (Figure 2f). It is clearly seen that Fe intensively distributes in the core and shell, O mostly distributes in the shell, while C uniformly distributes in the whole material, in good agreement with the STEM observation results. Combing with the XPS and TEM results, the core-shell structured nanoparticle is composed of Fe3C, Fe/Fe3O4 and C as the Fe3C@Fe/Fe3O4/C composite. The SEM and TEM images (Figure S1) demonstrate that FeOx/C-1.8-600 and FeOx/C-1.8-800 also possess the similar 3D honeycomblike structure, which are also embedded with core-shell structured nanoparticles. The EDS mapping results of the samples exhibit the uniform dispersion of Fe, O, C and N elements in the composite (Figure S2).


8

Page 9 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. (a) SEM image, (b-d) TEM images, (e) STEM image and (f) EDS mapping of FeOx/C1.8-700 composite. Moreover, it is found that the content of Fe(NO3)3∙9H2O is also a key factor influencing the phases and morphologies of the product. As shown in Figure S3, the main phase of FeOx/C-1.5700 is Fe3C, which is similar to FeOx/C-1.8-700. But when the addition of Fe(NO3)3∙9H2O increases to 2.1 g, the main phase of FeOx/C-2.1-700 transforms into Fe3C and Fe3O4. The XPS analytic results of FeOx/C-1.5-700 and FeOx/C-2.1-700 confirm the oxidation states of Fe 2p and C 1s in such composites (Figure S4). From the SEM images (Figure S5), it can be observed that FeOx/C-1.5-700 also presents the similar honeycomb-like structure with FeOx/C-1.8-700. But the microstructure of FeOx/C-2.1-700 is changed to pieces of irregular nanosheets. Also, substantial nanoparticles with the diameter of 50~100 nm can be observed on the surface of each pieces. Consequently, it can be inferred that the formation of the honeycomb-like nanostructure could be


9


Page 10 of 22

related to the decomposition of PVP which releases a huge volume of gas to form porous structures during pyrolysis. The higher content of Fe(NO3)3∙9H2O brings more gas release and causes the change of the nanostructure. EDS mapping images illustrate that FeOx/C-1.5-700 and FeOx/C-2.1700 also consist of Fe, O, C and N elements (Figure S6). According to the EDS mapping results, the content of Fe3O4, Fe/Fe3C and N-doped carbon is listed in Table S1. It can be seen that FeOx/C1.5-600 possesses the highest content of Fe3O4. The specific surface areas and porous structure of FeOx/C samples were investigated via N2 adsorption/desorption isotherms at 77 K. The Brunauer-Emmett-Teller (BET) curves (Figure S7a) reveal type IV nitrogen adsorption/sorption isotherms. The pore size distribution (Figure S7b) of these materials ranges from 3 to 6 nm, indicating a mesoporous structure of the FeOx/C composites. As listed in Table S2, FeOx/C-1.8-700 presents high BET surface area (243 m2 g-1) and pore volume (0.322 cm3 g-1), indicating the high porosity. The morphology and porosity characterization confirm that 3D honeycomb-like nanostructured composites embedded with Fe/Fe3C/Fe3O4 nanoparticles have been easily obtained. The integral porous structure supplies high BET surface areas and abundant ion/electron transport pathways. Moreover, the carboncoating structure helps to avoid the direct contact of FeOx nanoparticles with electrolyte. The unique components and nanostructures are beneficial for improving the lithium storage performance. 3.2. Electrochemical properties The electrochemical properties of FeOx/C composites were investigated as anode for LIBs. The cyclic voltammograms (CV) curves were measured at a scan rate of 0.1 mV s-1. Figure 3a shows the CV curves of FeOx/C-1.8-700 electrode. In the initial cycle, the appearance of the well-defined reduction peak at ~0.6 V (vs. Li+/Li) can be attributed to the production of solid electrolyte


10

Page 11 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


interface (SEI) film and the conversion of Fe3O4 to Fe metal, while the big slope can be indexed to Li+ insertion into carbon.31 The reduction peak shifts to 0.8 V arising from the polarization along with cycling.28 The two oxidation peaks presenting at ~1.7 and ~1.9 V can be indexed to the reversible oxidation of Fe. It is noted that after the first cycle, the CV curves overlapped well, indicating good cycling stability of the electrode and illustrating that stable SEI film was formed. The CV files of other FeOx/C electrodes present similar shape, however, their areas are smaller (Figure S8), indicating the highest specific capacity of FeOx/C-1.8-700.

Figure 3. Electrochemical performance of the as-prepared FeOx/C composites. (a) CV curves and (b) charge-discharge curves of the FeOx/C-1.8-700 electrode. (c) Cycle life of the FeOx/C electrodes at 0.2 A g-1 and (d) rate performance of the FeOx/C electrodes at various current densities. (e) Long-term cycling performance of FeOx/C-1.8-700 electrode at 5 A g-1.


11


Page 12 of 22

Figure 3b displays the charge-discharge curves of selected cycles of FeOx/C-1.8-700 at 0.2 A g1

. The initial discharge curve with a large slope presents a voltage plateau at ~0.7 V (vs. Li+/Li),

which agrees well with the CV profiles. In the following cycles, the charge-discharge curves overlapped well. The initial discharge/charge specific capacities of FeOx/C-1.8-700 are 997.7/727.4 mAh g-1, displaying a high initial coulombic efficiency (73%). In the 2nd cycle, the electrode delivers a discharge capacity of 735.5 mAh g-1. The irreversible formation of SEI layers can account for such capacity loss. In the following cycles, the specific capacity increases to 1242 mAh g-1 after 100 cycles, indicating a long active process of the electrode. The cycle life of the FeOx/C electrodes was tested at 0.2 A g-1. As shown in Figure 3c, all the electrodes need an activation process, which may because the electrochemical nano effect takes place during the cycling process.38 It is noted that FeOx/C-1.8-600 delivers the highest initial discharge capacity. After the activation process, the specific capacity tends stable. Specially, after 120 cycles, FeOx/C-1.8-700 delivers the highest discharge capacity of 1295.0 mAh g-1. It is found that the FeOx/C electrodes deliver much higher specific capacity than their theoretical capacities. The extra capacity may derive from the reversible formation/decomposition of some components in SEI film due to the electrochemical catalysis of Fe/Fe3C.28, 29 The rate capability of the FeOx/C electrodes was studied at different current densities from 0.2 to10 A g-1 (Figure 3d). It is revealed that the FeOx/C-1.8-600 electrode displays the highest specific capacity at relatively low current densities from 0.2 to 2.0 A g-1, while decreases quickly at higher current densities. Obviously, the FeOx/C-1.8-700 electrode presents the superior rate performance. It delivers average capacities of 809, 792, 755, 654, 532 and 354 mA h g-1 at 0.2, 0.5, 1.0, 2.0, 5.0 and 10 A g-1, respectively. When the current density is back to 0.2 A g-1, it still increases to 863 mAh g-1, displaying outstanding ability towards tolerating the current change. The long-term


12

Page 13 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


cycling performance of the FeOx/C-1.8-700 electrode was evaluated at 5 A g-1. As shown in Figure 3e, the initial discharge/charge specific capacities are 990.2/550 mAh g-1, respectively, showing the coulombic efficiency of 56%. In the following cycles, the coulombic efficiency maintains at ~99%. After 500 cycles, the retained discharge capacity is still 345.5 mAh g-1, demonstrating superior high-rate cycling stability.

Figure 4. Nyquist plots of the as-prepared FeOx/C electrodes measured at the open-circuit potential (inset is the equivalent circuit). Table S3 shows that compared with the previous studies, the FeOx/C-1.8-700 electrode displays better or comparable cyclic stability and rate performances. The superior electrochemical properties of FeOx/C electrodes may be due to their novel structure features. First, the honeycomblike graphitic carbon conductive networks provide fast ion diffusion and electron migration pathway, thus improving the electrode kinetics and leading to the enhanced rate performance. Figure 4 exhibits the Nyquist plot of the electrode with a semi-circle in the high-frequency region, followed by a linear slope in the low-frequency region. By fitting by Zview Software, the FeOx/C1.8-700 electrode presents the lowest charge transfer resistance of 70.12 Ω, proving the good charge-transfer kinetics of the electrode.39 Second, in terms of the stable network structure, the integrity of the electrode can be maintained, thus insuring the excellent cyclic stability of as-


13


Page 14 of 22

prepared composites. As presented in Figure 5c and 5d, after 100 cycles, the electrode presents only small cracks, and the active materials are still uniformly trapped in the carbon matrix. HRTEM images shown in Figure 5e and 5f illustrate that after a lithiation-delithiation process, the nanoparticles are transformed into smaller nanocrystals, which improves the usage of active materials and results in the increase of specific capacity. It is clearly observed that the nanocrystals are still encapsulated in each carbon shell without any aggregation, demonstrating that the encapsulated structure effectively buffers the volume change and agglomeration of nanoparticles during the charge-discharge process.

Figure 5. (a) SEM image and (b) TEM image of the freshly prepared FeOx/C-1.8-700 electrode. (c) SEM image and (d-f) TEM images of the FeOx/C-1.8-700 electrode after 100 cycles at 5 A g1

.

4. CONCLUSIONS In summary, a 3D honeycomb-like carbon network encapsulated Fe/Fe3C/Fe3O4 composite has been successfully fabricated based on the metal catalysis mechanism. The interconnected graphitic


14

Page 15 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


carbon matrix not only provides efficient ion diffusion and fast electron migration, but also prevents the exposure of Fe/Fe3C/Fe3O4 nanoparticles to electrolyte, thus endowing the material with good electrode kinetics and excellent structural stability. Moreover, the presence of metal Fe/Fe3C further improves the conductivity of the composite and can acts as electrocatalyst for the reversible reaction of some components in SEI film, which brings about extra capacity. As anode for LIBs, the electrode (FeOx/C-1.8-700) displays high initial discharge capacity of 997.7 mAh g1

as well as reversible discharge capacity of 1295.0 mAh g-1 after 120 cycles at 0.2 A g-1. At high

current densities, it also delivers superior cycling stability (345.5 mAh g-1 after 500 cycles at 5 A g-1) and high coulombic efficiency (~99% at 5 A g-1). Undoubtedly, our simple and high-yield strategy could be extended to the construction of other interesting materials with stable and ultrafast lithium storage properties. ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge via the Internet at http://pubs.acs.org. Detailed experimental section, Figures showing the crystal structure, morphology, N2 adsorption-desorption isotherm, pore size distribution and lithium storage properties of FeOx/C composites, the TEM images of FeOx/C-1.8-700 and its morphology after long cycles. And comparison of the electrochemical properties of the as-prepared and the FeOx/C composites and the previously reported Fe3C-based materials. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (Q. H. Wang) [email protected] (X. S. Zhao) Notes The authors declare no competing financial interest. ACKNOWLEDGMENT


15


Page 16 of 22

This work is supported by Natural Science Foundation of Jiangsu Province (BK20160213), National Natural Science Foundation of China (51702138, 21776119) and Postgraduate

Research

&

Practice

Innovation

Program

of

Jiangsu

Province

(KYCX17_1584). REFERENCES (1) Cheng, X. B.; Zhang, R.; Zhao, C. Z.; Zhang, Q., Toward Safe Lithium Metal Anode in Rechargeable Batteries: A Review. Chem. Rev. 2017, 117, 10403-10473. (2) Xu. J. T; Dou, Y. H.; Wei, Z. X.; Ma, J. M; Deng, Y. H.; Li, Y. T.; Liu, H. K.; Dou, S. X., Recent Progress in Graphite Intercalation Compounds for Rechargeable Metal (Li, Na, K, Al)-Ion Batteries. Adv. Sci. 2017, 4, 1700146. (3) Etacheri, V.; Marom, R.; Elazari, R.; Salitra, G.; Aurbach, D., Challenges in the Development of Advanced Li-Ion Batteries: A Review. Energy Environ. Sci. 2011, 4, 3243-3262 (4) Croguennec, L.; Palacin, M. R., Recent Achievements on Inorganic Electrode Materials for Lithium-Ion Batteries. J. Am. Chem. Soc. 2015, 137, 3140-3156. (5) Zhou, T. F.; Zheng, Y.; Gao, H.; Min, S. D.; Li, S.; Liu, H. K.; Guo, Z. P., Surface Engineering and Design Strategy for Surface Amorphized TiO2@Graphene Hybrids for High Power Li-Ion Battery Electrodes. Adv. Sci. 2015, 2, 1500027. (6) Liu, Y. J.; Tai, Z. X.; Zhou, T. F.; Sencadas, V.; Zhang, J.; Zhang, L.; Konstantinov, K.; Guo, Z. P.; Liu H. K., An All-Integrated Anode via Interlinked Chemical Bonding between DoubleShelled–Yolk-Structured Silicon and Binder for Lithium-Ion Batteries. Adv. Mater. 2017, 29, 1703028.


16

Page 17 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(7) Wei, W.; Yang, S. B.; Zhou, H. X.; Lieberwirth, I.; Feng, X. L.; Mullen, K., 3D Graphene Foams Cross-Linked with Pre-encapsulated Fe3O4 Nanospheres for Enhanced Lithium Storage. Adv. Mater. 2013, 25, 2909-2914. (8) Wu, C.; Maier, J.; Yu, Y., Generalizable Synthesis of Metal-Sulfides/Carbon Hybrids with Multiscale, Hierarchically Ordered Structures as Advanced Electrodes for Lithium Storage. Adv. Mater. 2016, 28, 174-180. (9) Kang, N.; Park, J. H.; Choi, J.; Jin, J.; Chun, J.; Jung, I. G.; Jeong, J.; Park, J. G.; Lee, S. M.; Kim, H. J.; Son, S. U., Nanoparticulate Iron Oxide Tubes from Microporous Organic Nanotubes as Stable Anode Materials for Lithium Ion Batteries. Angew. Chem. Int. Ed. 2012, 51, 6626-6630. (10) Hahn, B. P.; Long, J. W.; Mansour, A. N.; Pettigrew, K. A.; Osofsky, M. S.; Rolison, D. R., Electrochemical Li-Ion Storage in Defect Spinel Iron Oxides: the Critical Role of Cation Vacancies. Energy Environ. Sci. 2011, 4, 1495-1502. (11) Wang, Z. Y.; Zhou, L.; Lou, X. W. D., Metal Oxide Hollow Nanostructures for LithiumIon Batteries. Adv. Mater. 2012, 24, 1903-1911. (12) Poizot, P.; Laruelle, S.; Grugeon, S.; Dupont, L.; Tarascon, J.-M., Nano-Sized TransitionMetal Oxides as NegativeElectrode Materials for Lithium-Ion Batteries. Nature 2000, 407, 496499. (13) Cao, K. Z.; Jiao, L. F.; Liu, H. Q.; Liu, Y. C.; Wang, Y. J.; Guo, Z. P.; Yuan, H. T., 3D Hierarchical Porous α-Fe2O3 Nanosheets for High-Performance Lithium-Ion Batteries. Adv. Energy Mater. 2015, 5, 1401421.


17


Page 18 of 22

(14) Zeng, T.; Yu, M. D.; Zhang, H. Y.; He, Z. Q.; Chen, J. M.; Song, S., Fe/Fe 3C@N-Doped Porous Carbon Hybrids Derived from Nanoscale MOFs: Robust and Enhanced Heterogeneous Catalyst for Peroxymonosulfate Activation. Catal. Sci. Technol. 2017, 7, 396-404. (15) Li, J. X.; Zou, M. Z.; Chen, L. Z.; Huang, Z. G.; Guan, L. H., An Efficient Bifunctional Catalyst of Fe/Fe3C Carbon Nanofibers for Rechargeable Li–O2 Batteries. J. Mater. Chem. A 2014, 2, 10634-10638. (16) Giordano, C.; Kraupner, A.; Fleischer, I.; Henrich, C.; Klingelhöfer, G.; Antonietti, M., Non-Conventional Fe3C-Based Nanostructures. J. Mater. Chem. 2011, 21, 16963-16967. (17) Yang, S. B.; Feng, X. L.; Ivanovici, S.; Mullen, K., Fabrication of Graphene-Encapsulated Oxide Nanoparticles: Towards High-Performance Anode Materials for Lithium Storage. Angew. Chem. Int. Ed. 2010, 49, 8408-8411. (18) Ji, L. W.; Lin, Z.; Alcoutlabi, M.; Zhang, X. W., Recent Developments in Nanostructured Anode Materials for Rechargeable Lithium-Ion Batteries. Energy Environ. Sci. 2011, 4, 26822699. (19) Wu, Y.; Wei, Y.; Wang, J. P.; Jiang, K. L.; Fan, S. S., Conformal Fe3O4 Sheath on Aligned Carbon Nanotube Scaffolds as High-Performance Anodes for Lithium Ion Batteries. Nano Lett. 2013, 13, 818-823. (20) Chen, Y.; Song, B. H.; Li, M.; Lu, L.; Xue, J. M., Fe3O4 Nanoparticles Embedded in Uniform Mesoporous Carbon Spheres for Superior High-Rate Battery Applications. Adv. Funct. Mater. 2014, 24, 319-326.


18

Page 19 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(21) Chen, S. Q.; Bao, P. T.; Wang, G. X., Synthesis of Fe2O3-CNT-Graphene Hybrid Materials with An Open Three-Dimensional Nanostructure for High Capacity Lithium Storage. Nano Energy 2013, 2, 425-434. (22) Wang, X. B.; Zhang, Y. J.; Zhi, C. Y.; Wang, X. W.; Tang, D. M.; Xu, Y. B.; Weng, Q. H.; Jiang, X. F.; Mitome, M.; Golberg, D.; Bando, Y., Three-Dimensional Strutted Graphene Grown by Substrate-Free Sugar Blowing for High-Power-Density Supercapacitors. Nat. Commun. 2013, 4, 2905-2912. (23) Tian, M.; Wang, W.; Liu, Y.; Jungjohann, K. L.; Harris, C. T.; Lee, Y.-C.; Yang, R. G., A Three-Dimensional Carbon Nano-Network for High Performance Lithium Ion Batteries. Nano Energy 2015, 11, 500-509. (24) Ji, J. P.; Song, X. F.; Liu, J. Z.; Yan, Z.; Huo, C. X.; Zhang, S. L.; Su, M.; Liao, L.; Wang, W. H.; Ni, Z. H.; Hao, Y. F.; Zeng, H. B., Two-Dimensional Antimonene Single Crystals Grown by Van Der Waals Epitaxy. Nat. Commun. 2016, 7, 13352-13360. (25) Li, M.; Du, H.; Kuai, L.; Huang, K. F.; Xia, Y. Y.; Geng, B. Y., Scalable Dry-Production of Superior 3D Net-Like FeOx/C Composite Anode Material for Lithium Ion Battery. Angew. Chem. Int. Ed. 2017, 56, 12649-12653. (26) Wang, Q. H.; Zhang, W. C.; Guo, C.; Liu, Y.; Wang, C.; Guo, Z. P., In Situ Construction of 3D Interconnected FeS@Fe3C@Graphitic Carbon Networks for High-Performance Sodium-Ion Batteries. Adv. Funct. Mater. 2017, 27, 1703390.


19


Page 20 of 22

(27) Su, L. W.; Zhong, Y. R.; Zhou, Z., Role of Transition Metal Nanoparticles in the Extra Lithium Storage Capacity of Transition Metal Oxides: A Case Study of Hierarchical Core-Shell Fe3O4@C and Fe@C Microspheres. J. Mater. Chem. A 2013, 1, 15158-15166. (28) Su, L. W.; Zhou, Z.; Shen, P. W., Core–Shell Fe@Fe3C/C Nanocomposites as Anode Materials for Li Ion Batteries. Electrochim. Acta 2013, 87, 180-185. (29) Su, L. W.; Zhou, Z.; Shen, P. W., Ni/C Hierarchical Nanostructures with Ni Nanoparticles Highly Dispersed in N-Containing Carbon Nanosheets: Origin of Li Storage Capacity. J. Phys. Chem. C 2012, 116, 23974-23980. (30) Zhang, J. N.; Wang, K. X.; Xu, Q.; Zhou, Y. C.; Cheng, F. Y.; Guo, S. J., Beyond Yolk Shell Nanoparticles: Fe3O4@Fe3C Core@Shell Nanoparticles as Yolks and Carbon Nanospindles as Shells for Efficient Lithium Ion Storage. ACS Nano 2015, 9, 3369-3376. (31) Zhou, J. Q.; Qian, T.; Yang, T. Z.; Wang, M. F.; Guo, J.; Yan, C. L., Nanomeshes of Highly Crystalline Nitrogen-Doped Carbon Encapsulated Fe/Fe3C Electrodes as Ultrafast and Stable Anodes for Li-Ion Batteries. J. Mater. Chem. A 2015, 3, 15008-15014. (32) Tang, D.-M.; Liu, C.; Yu, W.-J.; Zhang, L.-L.; Hou, L.-L.; Li, J.-C.; Li, F.; Bando, Y.; Golberg, D.; Cheng, H.-M., Structural Changes in Iron Oxide and Gold Catalysts during Nucleation of Carbon Nanotubes Studied by In Situ Transmission Electron Microscopy. ACS Nano 2014, 8, 292-301. (33) Yang, Y.; Fan, X. J.; Casillas, G.; Peng, Z. W.; Ruan, G. D.; Wang, G.; Yacaman, M. J.; Tour, J. M., Three-Dimensional Nanoporous Fe2O3/Fe3C-Graphene Heterogeneous Thin Films for Lithium-Ion Batteries. ACS Nano 2014, 8 3939-3946.


20

Page 21 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(34) Pan, W. W.; Han, R.; Chi, X.; Liu, Q. F.; Wang, J. B., Ferromagnetic Fe3O4 Nanofibers: Electrospinning Synthesis and Characterization. J. Alloys and Compounds 2013, 577, 192-194. (35) Yu, Z. L.; Xin, S.; You, Y.; Yu, L.; Lin, Y.; Xu, D. W.; Qiao, C.; Huang, Z. H.; Yang, N.; Yu, S. H.; Goodenough, J. B., Ion-Catalyzed Synthesis of Microporous Hard Carbon Embedded with Expanded Nanographite for Enhanced Lithium/Sodium Storage. J. Am. Chem. Soc. 2016, 138, 14915-14922. (36) Liu, B. Q.; Zhang, Q.; Jin, Z. S.; Zhang, L. Y.; Li, L.; Gao, Z. G.; Wang, C. G.; Xie, H. M.; Su, Z. M., Uniform Pomegranate-Like Nanoclusters Organized by Ultrafine Transition Metal Oxide@Nitrogen-Doped Carbon Subunits with Enhanced Lithium Storage Properties. Adv. Energy Mater. 2018, 8, 1702347. (37) Li, J. X.; Wen, W. W.; Xu, G. G.; Zou, M. Z.; Huang, Z. G.; Guan, L. H., Fe-added Fe3C Carbon Nanofibers as Anode for Li Ion Batteries with Excellent Low-Temperature Performance. Electrochem. Acta 2015, 153, 300-305. (38) Dou, Y. H.; Xu J. T.; Ruan, B. Y.; Liu, Q. N.; Pan, Y. D.; Sun, Z. Q.; Dou, S. X., Atomic Layer-by-Layer Co3O4/Graphene Composite for High Performance Lithium-Ion Batteries. Adv. Energy Mater. 2016, 6, 1501835. (39) Dou, Y. H.; Wang, Y. X.; Tian, D. L.; Xu, J. T.; Zhang, Z. J.; Liu, Q. N.; Ruan, B. Y.; Ma, J. M; Sun, Z. Q.; Dou, S. X., Atomically Thin Co3O4 Nanosheet-Coated Stainless Steel Mesh with Enhanced Capacitive Na+ Storage for High-Performance Sodium-Ion Batteries. 2D Mater. 2017, 4, 015022.


21


Page 22 of 22

Table of Contents Graphic


22

Facile Fabrication of Honeycomb-like Carbon Network-Encapsulated

Recommend Documents