Dual hybrid strategy towards achieving high capacity and long-life lithium storage of ZnO

Journal of Power Sources 305 (2016) 1e9

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Dual hybrid strategy towards achieving high capacity and long-life lithium storage of ZnO Ying Xiao a, b, Minhua Cao a, * a Key Laboratory of Cluster Science, Ministry of Education of China, Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials, Department of Chemistry, Beijing Institute of Technology, Beijing 100081, PR China b College of Chemical Engineering, Nanjing Forestry University, Nanjing 210037, PR China

h i g h l i g h t s

g r a p h i c a l a b s t r a c t


The ZnO-based hybrid (ZnO/Co/CeN) is prepared from metal-organic frameworks.
ZnO/Co/CeN displays super lithium storage performance when used as an anode.
The excellent property is attributed to its unique composition and microstructure.

a r t i c l e i n f o

a b s t r a c t

Article history: Received 17 August 2015 Received in revised form 2 November 2015 Accepted 18 November 2015 Available online xxx

In this work, we propose a facile and efficient strategy for mitigating capacity fading of ZnO by cohybridization of cobalt (Co) and N-doped carbon (CeN). The ZnO-based hybrid (ZnO/Co/CeN) is prepared by calcining metal-organic frameworks (MOFs) under a vacuum condition. In view of the unique microstructure of MOFs used in our case, the resultant hybrid displays a three dimensional (3D) spherical morphology with abundant pore structure. The electrochemical tests indicate that the ZnO/Co/CeN nanospheres exhibit excellent cycling stability, high specific capacity, and good rate capability. This work proposes a facile strategy for the synthesis of nanomaterials with unique microstructure, desired composition and high surface area, endowing an excellent lithium storage performance. The current route is convenient and cost-effective, and therefore it is highly promising for scaled-up production. Moreover, the method we adopted may be extended to synthesize other porous nanomaterials with desired composition. © 2015 Elsevier B.V. All rights reserved.

Keywords: Metal-organic frameworks Zinc oxide Porous Nanospheres Lithium ion batteries

1. Introduction Metal-organic frameworks (MOFs) represent a new class of organic-inorganic hybrid materials comprised of ordered networks formed from organic electron donor linkers and metal cations, and

* Corresponding author. E-mail address: [email protected] (M. Cao). http://dx.doi.org/10.1016/j.jpowsour.2015.11.071 0378-7753/© 2015 Elsevier B.V. All rights reserved.

they have great potential for wide applications in drug delivery, catalysis, and gas storage [1e3]. Owing to their novel microstructure and tunable composition, MOFs with various morphologies and architectures have been used as precursors and templates for constructing novel nanoporous materials with intriguing properties. For instance, Kurungot et al. reported N-doped carbon with a high surface area from Zn4O (1,4-benzenedicarboxylate)3 (MOF-5), which exhibits excellent oxygen reduction reaction (ORR) activity in alkaline medium [4]. Using prussian blue as a precursor, Lou's

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group prepared porous Fe2O3 and proposed a general approach for the preparation of complex hollow boxes including Fe2O3/SnO2, Fe2O3/B2O3, and Fe2O3/SiO2 [2,5,6], in which the resultant Fe2O3based hollow boxes can be used as an anode material for lithium ion batteries (LIBs) due to their unique microstructure. Microporous carbon polyhedrons were obtained from zeolite imidazolate framework-8 (ZIF-8) and they can serve as a promising host to incorporate sulphur for high-performance LieS battery [7]. Chen and his co-workers prepared various porous or hollow nanomaterials by using prussian blue analogues, such as Co3O4 cages, Ag/Co3O4 composites, and hollow SiO2 cubes, and their applications in electrochemical field were investigated as well [8e10]. Besides, LiCoO2 cubes, CuO spheres, CeO2 nanobars, Fe2O3/MOx (M ¼ Cu, Ni, Co) composites were also prepared from MOFs-based precursors [11e14]. With the increasing demands for electric vehicles and hybrid electric vehicles with long-life, high capacity and energy density, LIBs are facing a great challenge in searching for alternative anode materials for commercial graphite. In the past years, a variety of metal-based materials especially transition metal oxides have been developed as potential anodes owing to their high theoretical capacities [15e19]. Recently, zinc oxide (ZnO) as a potential anode material in LIBs has gained particular attention owing to its high theoretical capacity (987 mAh g1) and attractive features including low processing lost, non-toxicity, natural abundance, and environmental benignity [20e27]. The lithium insertion-extraction mechanism in ZnO is similar to that in SnO2 including reversible conversion reaction and alloying/dealloying process. However, its lithium storage performance is usually accompanied by poor electrochemical kinetics and severe capacity fading upon the extended cycling, thus limiting its wide applications [21,22,28]. Therefore, it is significant to develop an efficient strategy to overcome these issues. Generally, for electrode materials, doping with heteroatoms, compositing with conductive materials, and constructing porous microstructure have been proved to be powerful approaches to improve the electrochemical properties of the host materials. These strategies can improve the electronic conductivity of the host materials, alleviate the volume changes during the discharge/charge process and shorten the transport path of Li-ion and electron efficiently [29e32], thus enhancing the reaction kinetics and achieving long-life and high-capacity performance. Therefore, those MOFsbased materials with rich transition metals, carbon and nitrogen elements can be easily prepared and could be ideal solid-phase precursors for the synthesis of electrode materials. In this work, we propose a facile and efficient strategy to achieve high-performance lithium storage of ZnO via hybridization with conductive cobalt (Co) and N-doped carbon (CeN). Here, Zn3 [Co(CN)6]2/polyvinyl pyrrolidone (PVP) nanospheres (NSs) {Zn3 [Co(CN)6]2/PVP NSs}, a MOF-based precursor, was directly subjected to calcining under a vacuum condition, and then ZnO/Co/Ndoped carbon NSs (ZnO/Co/CeN NSs) were obtained. The resultant ZnO/Co/CeN NSs possess a mesoporous structure with a surface area as high as 104.2 m2 g1. As a result of the unique microstructure and composition, ZnO/Co/CeN NSs exhibit high lithium storage capacity and superior rate capability when evaluated as an anode material in LIBs. This approach will open new opportunities for the rational design of metals/metal-oxides based materials with tunable compositions, which may find applications in energy conversion and storage. 2. Experimental 2.1. Synthesis of ZnO/Co/CeN The Zn3 [Co(CN)6]2/PVP precursor was first prepared using a

facile ultrasonic approach according to our previous work [29a,33]. In a typical synthesis, 0.132 g of zinc acetate {Zn (ac)2$2H2O} and 1.112 g of PVP (K30) were dissolved in 20 mL distilled water under magnetic stirring to form a transparent solution. Then, 20 mL of 0.02 M K3 [Co(CN)6] aqueous solution was slowly added into the former solution dropwise within 20 min under agitated stirring and ultrasonic radiation in an ice-water bath. Subsequently, the reaction was further kept for 1 h and aged at room temperature for 24 h. To fabricate the target product of ZnO/Co/CeN NSs, the resultant Zn3 [Co(CN)6]2/PVP precursor was calcined under a vacuum condition (0.1 MPa) at 600  C with a heating rate of 3  C min1 for 2 h. Co/CeN hybrid was obtained in the absence of Zn-salt and ZnO/C was formed without the addition of Co-salt, while keeping other conditions constant.

2.2. Characterizations Bruker D8 X-ray power diffactometer was applied to characterize the phase and composition of samples. The used voltage and current were 40 kV and 50 mA, respectively. The scanning range (2q) was from 10 to 80 with a scan rate of 5 min1. Microstructure of samples was investigated by field emission scanning electron microscopy (FE-SEM, JEOL S-4800 SEM unit) and transmission electron microscopy (TEM, JEOL 2100F) along with energy dispersive spectrometer (EDS). FEI Technai G2 F20 was used to give the scanning transmission electron microscope (STEM) mapping images. X-ray photoelectron spectra (XPS) were recorded on an ESCALAB 250 spectrometer (PerkineElmer) to further characterize the chemical composition of the hybrid. High-resolution spectra were carried out with the pass energy of 20 eV and the energy step of 0.1 eV. The elemental analysis was carried out on an elemental analyzer (Vario EI) by a conventional carbon-hydrogen-nitrogen (CHN) combustion method. Inductively-coupled plasma spectrometry (ICP) was carried out on a Jarrel-ASH (ICAP-9000). Raman spectra were recorded on an Invia Raman spectrometer, with an excitation laser wavelength of 633 nm. The BrunauereEmmetteTeller (BET) surface area of as-synthesized samples was measured using a Belsorp-max surface area detecting instrument by N2 physisorption at 77 K.

2.3. Electrochemical measurements The electrochemical test was performed on a LAND CT2001A battery test system using a two-electrode cell. For the working electrode (anode), the active material, carbon black, and sodium carboxymethyl cellulose (CMC) binder with a weight ratio of 80:10:10 were ground in a mortar to make homogeneous slurry using deionized water as solvent. The as-formed slurry was casted onto Cu foil uniformly, which then was dried in a vacuum over at 120  C for 36 h. The dried electrode was assembled into coin cell (CR2025) in an argon-filled glovebox. Lithium foil was used as both counter electrode and reference electrode; 1 M solution of LiPF6 in ethylene carbonate (EC)/dimethyl carbonate (DMC)/diethyl carbonate (DEC) (1:1:1, vol%) served as an electrolyte. The mass loading of the active material is around 1.20 mg. The voltage window was in the range of 0.01e3 V. Cyclic voltammetry (CV) curves were recorded on a CHI-760E workstation at a scanning rate of 0.3 mV s1. The impedance spectra of the cell were measured by applying a sine wave with amplitude of 5 mV over the frequency range from 100 kHz to 0.01 Hz. The capacity for the ZnO/Co/CeN hybrid electrode is calculated based on the total weight of the ZnO and carbon.

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3. Results and discussion The preparation of Zn3 [Co(CN)6]2/PVP precursor and its transformation into ZnO/Co/CeN NSs were schematically illustrated in Fig. 1a. The Zn3 [Co(CN)6]2/PVP NSs (Fig. S1, Supporting Information) were first prepared with the assistance of ultrasonic radiation and mechanical stirring [29a,33]. The subsequent calcining treatment of the precursor at 600  C was conducted under 0.1 MPa. During this process, the Zn3 [Co(CN)6]2/PVP precursor was transformed into ZnO/Co/CeN NSs, which have been confirmed by X-ray diffraction (XRD) pattern. As displayed in Fig. 1b, all the diffraction peaks can be well matched with hexagonal ZnO (JCPDF No: 361451) and cubic Co (JCPDF No: 15-0806) [21,34,35], indicating this sample contains ZnO and Co phases. The CHN element analysis shows that carbon and nitrogen elements also exist in this sample and their contents are 1.5 wt% and 1.1 wt%, respectively. Raman spectrum displays two typical peaks at ca. 1345.2 and 1583.3 cm1 (Fig. S2), further confirming the presence of carbon in this hybrid. Besides, X-ray photoelectron spectroscopy (XPS) was further applied to characterize the chemical state and composition of the hybrid (Fig. 2). The obvious signals for Zn 2p, O 1s, C 1s, and Co 2p in the survey spectrum (Fig. 2a) reveal the coexistence of Zn, O, C, and Co elements in this hybrid. The high resolution spectrum of Zn 2p in Fig. 2b exhibits two distinct peaks, which can be assigned to Zn2þ, in agreement with those in literature [36]. The high resolution spectrum of O 1s (Fig. 2c) exhibits three peaks at ca. 530.4, 531.5, and 532.8 eV, corresponding to ZneO band, eOH, and C]O, respectively. Besides, the high resolution spectrum of Co 2p (Fig. 2d) clearly indicates the existence of Co0 (778.4 eV, 793.6 eV), Co2þ (780.9 eV, 786.1 eV), and Co3þ (796.6 eV, 802.8 eV) on the surface of the hybrid [29,37]. This result indicates that the Co nanoparticles were partially oxidized to CoOx on the surface, which is consistent with other observations for metals at the nanoscale [38,39]. Considering the fact that no diffraction peaks that were assigned to CoOx were detected in XRD pattern (Fig. 1b), we deduce that only a small amount of Co was oxidized. The N 1s XPS spectrum (Fig. 2e) suggests the presence of nitrogen in the hybrid and two obvious peaks at ca. 395.3 and 399.1 eV can be attributed to nitrogen atoms bonded to Zn or Co atom and pyrrolic nitrogen, respectively [29]. We believe the interaction between metal and nitrogen will have a positive effect on the electrochemical performance of the hybrid [29b]. The C 1s XPS spectrum can be deconvoluted into three peaks (Fig. 2f), the predominant CeC bond (284.4 eV), CeN bond (285.2 eV), and CeO band (286.5 eV). Inductive coupled plasma emission spectrometer (ICP) analysis gives the molar ratio of Zn to Co to be ca. 2.5:1, and therefore the

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content of each component in this hybrid is determined to be ca. 75.0 wt% for ZnO, 20.0 wt% for Co, 1.5 wt% for C and 1.1 wt% for N. Fig. 3a shows a low-magnification field emission scanning electron microscopy (FE-SEM) image of ZnO/Co/CeN hybrid. It can be clearly seen that this sample is composed of fairly uniform NSs with an average diameter of ca. 250 nm. The high-magnification FESEM image (Fig. 3b) further reveals that the NSs are assembled by smaller nanoparticles with the size of ca. 20 nm. Transmission electron microscopy (TEM) images (Fig. 3cee) disclose that the nanoparticles are homogeneously distributed but with a loose way, thus leading to the formation of some pores between particles. High resolution TEM (HR-TEM) images (Fig. 3f) recorded on different parts in Fig. 3g show the co-existence of ZnO (with interplane spacing of 0.25 nm) and Co (with interplane spacing of 0.20 nm). Also, we investigated different parts on a single nanosphere (Fig. 3i), and the clear lattice fringes observed from the edge (part 1) and the inner (part 2) can be assigned to different planes of ZnO phase. These results indicate the hybrid mainly consists of ZnO but with a small amount of Co and N-doped C. In order to further confirm this speculation, we performed energy dispersive spectrometer (EDS) analysis for ZnO/Co/CeN hybrid (Fig. 4a). The atomic ratio of Zn to Co was calculated to be 2.64:1, which is consistent with above ICP results. From EDS and ICP results, we can see that the actual Zn:Co ratio is larger than that (Zn:Co ¼ 1.5) calculated from Zn3 [Co(CN)6]2. The possible reason may be deep and close encapsulation of Co nanoparticles by N-doped carbon as well as strong interaction of Co with N. When we prepared the sample to test ICP, Co is difficult to dissolve completely, which may result in high Zn:Co ratio in ICP results. The corresponding mapping images clearly display the element composition and the homogeneous distribution of all elements (Fig. 4b). Additionally, the porosity nature of ZnO/Co/CeN NSs is further characterized by N2 adsorptionedesorption isotherms. As shown in Fig. 4c, the isotherms belong to type IV curves, indicative of a mesoporous structure. The mesopore may result from the open spaces formed between adjacent particles. The mesopore size determined by the pore size distribution curve is ca. 9.8 nm (Fig. 4d), which is basically in agreement with the TEM result. Such a pore structure endows the BrunauereEmmetteTeller (BET) surface area as high as 104.2 m2 g1. Usually, it is believed that this kind of porous structure will be beneficial for improving the electrochemical performance of materials. One possible reason may be that the pore channel will allow for more Li-ion transport in the electrolyte, ensuring a good contact of the electrolyte with the electrode [40,41]. As a consequence, high capacity and rate capability will be obtained accordingly.

Fig. 1. (a) Schematic illustration of the fabrication process of ZnO/Co/CeN NSs. (b) XRD pattern of ZnO/Co/CeN NSs obtained by calcining Zn3 [Co(CN)6]2/PVP NSs at 600  C under vacuum pressure of 0.1 MPa.

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Fig. 2. XPS spectra of the ZnO/Co/CeN NSs: (a) survey spectrum, high resolution spectra of (b) Zn 2p, (c) O 1s, (d) Co 2p, (e) N 1s, and (f) C 1s, respectively.

In view of its unique composition and microstructure, the resultant ZnO/Co/CeN hybrid would be expected to be particularly promising for lithium-storage. Fig. 5 shows cyclic voltammogram (CV) curves and discharge/charge profiles of ZnO/Co/CeN hybrid as well as commercial ZnO electrodes at a scan rate of 0.3 mV s1. For the CV curves of ZnO/Co/CeN hybrid (Fig. 5a), the reduction peak at ca. 0.09 V in the first cycle corresponds to the reduction from ZnO to Zn and the formation of LieZn alloy [24], and the other peak at ca. 1.66 V could be ascribed to the decomposition of electrolyte and the formation of solid electrolyte interface (SEI) film. After the first cycle, two new reduction peaks at ca. 0.67 and 1.28 V were observed, which represent the multiple reduction of ZnO and the formation of Li2O. The oxidation peaks at ca. 0.38, 0.54, and 0.70 V can be attributed to the multistep dealloying process of LieZn alloy and the decomposition of SEI film, while the peak at ca. 1.50 V is related to the formation of ZnO and the decomposition of Li2O [24,34,42,43]. As we know, Li2O is electrochemically inactive and is almost impossible to decompose under unprompted conditions. However, Li2O in situ formed electrochemically can be catalyzed by the Co nanoparticles existing in the hybrid to decompose [16]. The reversible formation and decomposition of Li2O are believed to take a crucial role for the high capacity of the ZnO/Co/CeN hybrid. Furthermore, the CV curves coincide with each other after the first cycle, suggesting highly electrochemical reversibility of the hybrid upon further sweeps. This result is matched well with that of the discharge/charge profiles (Fig. 5b). The CV curves (Fig. 5c) and diacharge/charge profiles (Fig. 5d) for the commercial ZnO (other characterizations were presented in Fig. S4) are similar to those of ZnO/Co/CeN hybrid. However, unlike the ZnO/Co/CeN hybrid, the commercial ZnO exhibits rather unstable electrochemical performance. Based on the literature and above analysis [21,22], the electrochemical processes for the as-prepared electrode can be described as follows:

ZnO þ 2Liþ 4Zn þ Li2 O Zn þ xLiþ 4Lix Zn ðx  1Þ

(1) (2)

Fig. 6a presents the cycling performance of the ZnO/Co/CeN electrode as well as the commercial ZnO. The hybrid electrode with a current density of 100 mA g1 delivers initial discharge and

charge specific capacities of 1338.7 and 1134.7 mAh g1 with an initial Coulombic efficiency of 84.8% (blue curve in Fig. 6a). The capacity loss in the first cycle may originate from the incomplete conversion reaction and the formation of SEI layer [44,45]. It should be noted that the initial Coulombic efficiency is higher than those of most previously reported ZnO-based electrode materials, which may result from improved Li-cycling kinetic, leading to a reduced capacity loss from the incomplete conversion reaction [46]. The hybrid anode can maintain a reversible capacity as high as 1086.2 mAh g1 without apparent capacity loss after 100 cycles at a current density of 100 mA g1, demonstrating its excellent capacity retention. This value is evidently larger than the theoretical capacity of ZnO (987 mAh g1), which is common in other anode materials. The reason may be ascribed to the existence of interface lithium storage, the 3D porous structure, the formation of surface polymeric layer and the high conductivity components (NeC and metal Co) as well as the small-size ZnO particles [20,46e50]. More importantly, the Coulombic efficiency reaches nearly 100% after several cycles and keeps constant. Even cycled at the current density of 300 mA g1, the ZnO/Co/CeN electrode still delivers a high capacity of 757.0 mAh g1 after 100 cycles (red curve in Fig. 6a), which is much higher than that of the commercial ZnO cycled at 100 mA g1 (320.6 mAh g1). Furthermore, discernible capacity fluctuation for the ZnO/Co/CeN electrode is observed during cycling and this result may be attributed to the partial aggregation of particles, thus leading to inhomogeneous Liþ insertion and extraction in the active grains in different cycles [31]. Besides, we also evaluated the rate performance of the ZnO/Co/CeN anode, which was carried out from 100 mA g1 to 3000 mA g1 (Fig. 6b). As clearly displayed, the hybrid exhibits superior capacity rentation at various current densities, and even at a high current density of 3000 mAh g1 (where a discharge/charge process was completed within 12 min), a high capacity of 370.4 mAh g1 can still be achieved, demonstrating an excellent high-rate performance of the hybrid electrode. Moreover, even after two whole cycles at different current densities, the cell is still able to deliver a reversible capacity of 1090.4 mAh g1 when the current density returns back to 100 mAh g1. Such a rate performance of the ZnO/Co/CeN hybrid is better than most of high efficient ZnO-based materials previously reported (Fig. 6c) [20,30,40,44,50e55]. Furthermore, the long-life

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Fig. 3. (a,b) FE-SEM images of ZnO/Co/CeN hybrid. (cef) TEM images of ZnO/Co/CeN hybrid with different magnifications. (gei) High-magnified TEM and HRTEM images recorded on different areas of a single ZnO/Co/CeN nanosphere.

test was conducted at 1000 mA g1 for 1000 cycles (before testing, the cell was first activated at 100 mA g1 for 2 cycles). The reversible capacity can be stabilized at ca. 412.5 mAh g1 almost without decay, demonstrating a remarkable long-life performance of the current cell. For comparison, we also tested the cycling performance of the cells prepared with ZnO/C (without the addition of Co-based salts) and Co/CeN (without the addition of Znbased salts). As shown in Figs. S5 and S6, compared to the typical ZnO/Co/CeN hybrid, ZnO/C and Co/CeN both show low capacity and poor stability under the same test conditions. These results suggest the fact that Co, N-doped C, and porous 3D microstructure play important roles in the significantly improved electrochemical performance of ZnO. Additionally, Nyquist plot (Fig. 6d) of ZnO/Co/ CeN hybrid displays much smaller semicircle than that of commercial ZnO. The fitted results based on the relevant equivalent

circuit model indicate that the charge transfer resistances (Rct) of ZnO/Co/CeN hybrid and commercial ZnO are 9.5 and 40.6 U, respectively, further confirming significantly improved charge transfer ability of Li-ion at the interface between the electrolyte and electrode and better conductivity [56]. Fig. 7a,b shows SEM images of the ZnO/Co/CeN hybrid electrode after 100 cycles at 100 mA g1, from which it can be clearly seen that the porous spherical shape of ZnO/Co/CeN hybrid is perfectly retained, suggesting its superior structural stability. Additionally, the size of nanoparticles exhibits negligible changes, which may result from the existence of metaleN bond and N-doped C. On the one hand, metaleN bond can strengthen the interaction between active metal-based particles and CeN, preventing the agglomeration of metal nanoparticles generated during cycling [29], and on the other hand, N-doped C with a certain elastic property affords

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Fig. 4. (a) EDS spectrum and (b) element mapping images of ZnO/Co/CeN hybrid. (c) Nitrogen adsorptionedesorption isotherms and (d) pore size distribution curve of ZnO/Co/CeN hybrid.

Fig. 5. CV curves of ZnO/Co/CeN hybrid (a) and commercial ZnO (c). Discharge/charge curves of ZnO/Co/CeN hybrid (b) and commercial ZnO (d).

good dispersion of nanoparticles [57]. We concluded the ideal composition and the porous 3D microstructure that mainly contribute to the significantly improved lithium performance of the ZnO/Co/CeN hybrid in terms of the cycling stability, the capacity,

and the rate capability. The excellent electrochemical performance can be attributed to following five aspects: (1) The introduction of Co into ZnO not only improves the conductivity of the whole electrode and benefits the reversible decomposition of Li2O, but

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Fig. 6. (a) Cycle performance of ZnO/Co/CeN hybrid at current densities of 100 mA g1 and 300 mA g1 along with that of the commercial ZnO at a current density of 100 mA g1. The Coulombic efficiency of ZnO/Co/CeN hybrid at current density of 100 mA g1 is also displayed. (b) Rate performance of ZnO/Co/CeN hybrid and commercial ZnO at various current densities from 100 to 3000 mA g1. (c) The comparison of the rate performance of ZnO/Co/CeN with other literature. (d) Nyquist plots as well as the corresponding fitting results of ZnO/Co/CeN hybrid and commercial ZnO after 100 cycles at 100 mA g1. (e) Long-life test of ZnO/Co/CeN hybrid at a current density of 1000 mA g1.

Fig. 7. (a,b) FE-SEM images of ZnO/Co/CeN hybrid electrode after 100 cycles at 100 mA g1.

also can serve as a buffer media to alleviate massive volume expansion and contraction of ZnO during the cycling process

[58e61]; (2) The abundant pores can act as reservoirs for Li-ion storage, shorten the transport path length of Li-ion and electron,

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and alleviate the stress caused by volume change during intercalation/deintercalation of Li-ion to some extent [29,32,47,62,63]; (3) The existence of metaleN bond is beneficial for tight connection between ZnO and N-doped carbon, which is favourable for the stability of 3D structure, and counteracts the pulverization of electrode [29,64]; (4) Small content of N-doped C and N can increase the conductivity, stabilize the as-formed SEI film, induce more active sites, and partially alleviate the volume change during cycling [29,65,66]; (5) Small-size active nanoparticles can increase the specific surface in some extent, and enhance the interfacial lithium storage ability [67,68].

[17] [18] [19] [20] [21] [22]

4. Conclusions [23]

In summary, we have successfully designed and in situ synthesized ZnO/Co/CeN NSs by using MOF as a precursor. The resultant ZnO/Co/CeN hybrid displays spherical morphology with abundant porous structure. When evaluated as an anode material in LIBs, the ZnO/Co/CeN hybrid exhibits good cycling stability, excellent rate capability and long-life performance and it shows significant potential as a substitute for commercial graphite. It is proposed that the synergistic effects resulting from the unique composition and porous 3D microstructure of the ZnO/Co/CeN hybrid contribute to the outstanding electrochemical performance. The current method is cost efficient and can be scaled up. Furthermore, this method can be extended to synthesize other nanomaterials with similar microstructure by changing the metal ions. Acknowledgements

[24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35]

This work was financially supported by the National Natural Science Foundation of China (No. 21471016 and 21271023) and the 111 Project (B07012).

[36]

Appendix A. Supplementary data

[38] [39]

Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jpowsour.2015.11.071.

[40]

[37]

[41]

References

[42]

[1] (a) L. Hu, Q.W. Chen, Nanoscale 6 (2014) 1236; (b) C.X. Li, C.G. Hu, Y. Zhao, L. Song, J. Zhang, R.D. Huang, L.T. Qu, Carbon 78 (2014) 231. [2] L. Zhang, H.B. Wu, X.W. Lou, J. Am. Chem. Soc. 135 (2013) 10664. [3] P. Zhang, F. Sun, Z.H. Xiang, Z.G. Shen, J. Yun, D.P. Cao, Energy Environ. Sci. 7 (2014) 442. [4] S. Pandiaraj, H.Ba. Aiyappa, R. Banerjee, S. Kurungot, Chem. Comm. 50 (2014) 3363. [5] L. Zhang, H. B Wu, S. Madhavi, H.H. Hug, X.W. Lou, J. Am. Chem. Soc. 134 (2012) 17388. [6] L. Zhang, H.B. Wu, R. Xu, X.W. Lou, CrystEngComm 15 (2013) 9332. [7] H.B. Wu, S.Y. Wei, L. Zhang, R. Xu, H.H. Hng, X.W. Lou, Chem. Eur. J. 19 (2013) 10804. [8] N. Yan, L. Hu, Y. Li, Y. Wang, H. Zhong, X.Y. Hu, X.K. Kong, Q.W. Chen, J. Phys. Chem. C 116 (2012) 7227. [9] S.X. Bao, N. Yan, X.H. Shi, R. Li, Q.W. Chen, Appl. Catal. A Gen. 487 (2014) 189. [10] N. Yan, F. Wang, H. Zhang, Y. Li, Y. Wang, L. Hu, Q.W. Chen, Sci. Rep. 3 (2013) 1568. [11] P. Nie, L.F. Shen, H.F. Luo, H.S. Li, G.Y. Xu, X.G. Zhang, Nanoscale 5 (2013) 11087. [12] A. Banerjee, U. Singh, V. Aravindan, M. Srinivasan, S. Ogale, Nano Energy 2 (2013) 1158. [13] S. Maiti, A. Pramanik, S. Mahanty, Chem. Comm. 50 (2014) 11717. [14] X. Yang, Y.B. Tang, X. Huang, H.T. Xue, W.P. Kang, W.Y. Li, T.W. Ng, C.S. Lee, J. Power Sources 284 (2015) 109. [15] (a) S.L. Yang, B.H. Zhou, Z.P. Ding, H. Zheng, L.P. Huang, J. Pan, W. Wu, H.B. Zhang, J. Power Source 286 (2015) 124; (b) Y. Xiao, X. Wang, W. Wang, D. Zhao, M.H. Cao, ACS Appl. Mater. Interface 6 (2014) 2051. [16] (a) P. Poizot, S. Laruelle, S. Grugeon, L. Dupont, J.M. Tarascon, Nature 407 (2000) 496;

[43] [44]

[45] [46] [47] [48]

[49] [50] [51] [52] [53] [54] [55]

[56] [57] [58] [59] [60]

(b) Y.Y. Wang, X.J. Jiang, L.S. Yang, N. Jia, Y. Ding, ACS Appl. Mater. Interface 6 (2014) 1525; (c) S. Grugeon, S. Laruelle, R. Herrera-Urbin, L. Dupont, P. Poizot, J.M. Tarascon, J. Electrochem. Soc. 148 (2001) A285. X.H. Wang, Z.B. Yang, X.L. Sun, X.W. Li, D.S. Wang, P. Wang, D.Y. He, J. Mater. Chem. 21 (2011) 9988. X.H. Wang, L. Qiao, X.L. Sun, X.W. Li, D.K. Hu, Q. Zhang, D.Y. He, J. Mater. Chem. A 1 (2013) 4173. X.H. Wang, Y. Fan, R.A. Susantyoko, Q.Z. Xiao, L.M. Sun, D.Y. He, Q. Zhang, Nano Energy 5 (2014) 91. S.J. Yang, S. Nam, T. Kim, J.H. Im, H. Jung, J.H. Kang, S. Wi, B. Park, C.R. Park, J. Am. Chem. Soc. 135 (2013) 7394. M.P. Yu, A.J. Wang, Y.S. Wang, C. Li, G.Q. Shi, Nanoscale 6 (2014) 11419. (a) J.H. Huang, Z.H. Yang, X.E. Xie, Z.B. Feng, Z. Zhang, J. Power Source 289 (2015) 8; (b) G.Z. Yang, H.W. Song, H. Cui, Y.C. Liu, C.X. Wang, Nano Energy 2 (2013) 579. V. Cauda, D. Pugliese, N. Garino, A. Sacco, S. Bianco, F. Bella, A. Lamberti, C. Gerbaldi, Energy 65 (2014) 639. J.H. Lee, M.H. Hon, Y.W. Chung, I.C. Leu, Appl. Phys. A 102 (2011) 545. M. Laurenti, N. Garino, S. Porro, M. Fontana, C. Gerbaldi, J. Alloys Comp. 640 (2015) 321. Q.S. Xie, Y.T. Ma, D.Q. Zeng, L.S. Wang, G.H. Yue, D.L. Peng, Sci. Rep. 5 (2015) 8351. Q.S. Xie, D.Q. Zeng, Y.T. Ma, L. Lin, L.S. Wang, D.L. Peng, Electrochim. Acta 169 (2015) 283. Q.S. Xie, Y.T. Ma, D.Q. Zeng, X.Q. Zhang, L.S. Wang, G.H. Yue, D.L. Peng, ACS Appl. Mater. Interfaces 6 (2014) 19895. (a) Y. Xiao, P.P. Sun, M.H. Cao, ACS Nano 8 (2014) 7846; (b) X.S. Zhou, L.J. Wan, Y.G. Guo, Adv. Mater 25 (2013) 2152. Y.Y. Wang, X.J. Jiang, L.S. Yang, N. Jia, Y. Ding, ACS Appl. Mater. Interface 6 (2014) 1525. C.H. Jiang, M. Ichihara, I. Honma, H.S. Zhou, Electrochem. Acta 52 (2007) 6470. H.G. Hu, L.X. Wang, Y. Zhao, M.H. Ye, Q. Chen, Z.H. Feng, L.T. Qu, Nanoscale 6 (2014) 8002. D.J. Du, M.H. Cao, X.Y. He, Y.Y. Liu, C.W. Hu, Langmuir 25 (2009) 7057. M.O. Guler, T. Cetinkaya, U. Tocoglu, H. Akbulut, Microelectron. Eng. 118 (2014) 54. (a) L. Wang, Y. Yu, P.C. Chen, C.H. Chen, Scr. Mater 58 (2008) 405; (b) Z.Y. Wu, P. Chen, Q.S. Wu, L.F. Yang, Z. Pan, Q. Wang, Nano Energy 8 (2014) 118. K.T. Park, F. Xia, S.W. Kim, S.B. Kim, T. Song, U. Paik, W.I. Park, J. Phys. Chem. C 117 (2013) 1037. S.U. Awan, S.K. Hasanain, M.F. Bertino, G.H. Jaffari, J. Phys. Condens. Mater 25 (2013) 156005. C.G. Hu, X.Q. Zhai, L.L. Liu, Y. Zhao, L. Jiang, L.T. Qu, Sci. Rep. 3 (2013) 2065. C.G. Hu, X.Q. Zhai, Y. Zhao, K. Bian, J. Zhang, L.T. Qu, H.M. Zhang, H.X. Luo, Nanoscale 6 (2014) 2768. X.Y. Shen, D.B. Mu, S. Chen, B.R. Wu, F. Wu, ACS Appl. Mater. Interface 5 (2013) 3118. Y. Yan, Y.X. Yin, Y.G. Guo, L.J. Wan, Adv. Energy Mater. 4 (2014) 1301584, http://dx.doi.org/10.1002/aenm.201301584. S.M. Abbas, S.T. Hussain, S. Ali, N. Ahmad, N. Ali, S. Abbas, J. Mater. Sci. 48 (2013) 5429. M.O. Guler, O. Cevher, H. Akbulut, J. Nanosci. Nanotechnol. 12 (2012) 9118. (a) F. Zou, X.L. Hu, Z. Li, L. Qie, C.C. Hu, R. Zeng, Y. Jiang, Y.H. Huang, Adv. Mater. 26 (2014) 6622; (b) Z.L. Wang, D. Xu, H.G. Wang, Z. Wu, X.B. Zhang, ACS Nano 7 (2013) 2422. Z.Q. Zhu, S.W. Wang, J. Du, Q. Jin, T.R. Zhang, F.Y. Cheng, J. Chen, Nano Lett. 14 (2014) 153. L. Tian, H. Zou, J. Fu, X. Yang, Y. Wang, H. Guo, X. Fu, C. Liang, M. Wu, P. Shen, Q. Gao, Adv. Funct. Mater 20 (2010) 617. Y. Xiao, C.W. Hu, M.H. Cao, J. Power Source 247 (2014) 49. S. Xiong, J. Chen, X. Lou, H. Zeng, Adv. Funct. Mater 22 (2012) 861; (b) G. Binotto, D. Larcher, A. Prakash, R. Urbina, M. Hegde, J. Tarascon, Chem. Mater 19 (2007) 3032. G. Zhou, D. Wang, F. Li, L. Zhang, N. Li, Z. Wu, L. Wen, G. Lu, H. Cheng, Chem. Mater 22 (2010) 5306. Q.S. Xie, X.Q. Zhang, X.B. Wu, H.Y. Wu, X. Liu, G.F. Yue, Y. Yong, D.L. Peng, Electrochem. Acta 125 (2014) 659. R. Guo, W.B. Yue, Y.M. An, Y. Ren, X. Yan, Electrochem. Acta 135 (2014) 161. Z.M. Ren, Z.Y. Wang, C. Chen, J. Wang, X.X. Fu, C.Y. Fan, G.D. Qian, Electrochem. Acta 146 (2014) 52. M.P. Yu, A. Wang, Y.S. Wang, C. Li, G.Q. Shi, Nanoscale 6 (2014) 11419. S. Li, Y. Xiao, X. Wang, M.H. Cao, Phys. Chem. Chem. Phys. 16 (2014) 25846. (a) Q. Li, L.W. Yin, Z.Q. Li, X.K. Wang, Y.X. Qi, J.Y. Ma, ACS Appl. Mater. Interface 5 (2013) 10975; (b) G. Wang, Z.Y. Liu, P. Liu, Electrochim. Acta 56 (2011) 9515. A.K. Giri, P. Pal, R. Ananthakumar, M. Jayachandran, S. Mahanty, A.B. Panda, Cryst. Growth Des. 14 (2014) 3352. D.J. Xue, S. Xin, Y. Yan, K.C. Jiang, Y.X. Yin, Y.G. Guo, L.J. Wan, J. Am. Chem. Soc. 134 (2012) 2512. M.G. Kim, S. Sim, J. Cho, Adv. Mater 22 (2010) 5154. D. Deng, J.Y. Lee, Angew. Chem., Int. Ed. 48 (2009) 1660. L.J. Zhang, P. Hu, X.Y. Zhao, R. Tian, R.Q. Zou, D.G. Xia, J. Mater. Chem. 21

Y. Xiao, M. Cao / Journal of Power Sources 305 (2016) 1e9 (2011) 18279. [61] C.G. Hu, G.P. Zheng, F. Zhao, H.B. Shao, Z.P. Zhang, N. Chen, L. Jiang, L.T. Qu, Energy Environ. Sci. 7 (2014) 3699. [62] Z.Z. Li, W. Wang, Z.H. Li, Z.H. Qin, J. Wang, Z.P. Liu, J. Power Source 286 (2015) 534. [63] M.H. Chen, X.H. Xia, J.F. Yuan, J.H. Yin, Q.G. Chen, J. Power Source 288 (2015) 145.

9

[64] Y. Xiao, C.W. Hu, M.H. Cao, Chem. Asian J. 9 (2014) 351. [65] Y. Xia, Z. Xiao, X. Dou, H. Huang, X.H. Lu, R.J. Yan, Y.P. Gan, W.J. Zhu, J.P. Tu, W.K. Zhang, X.Y. Tao, ACS Nano 7 (2013) 7083. [66] J. Shin, W.H. Ryu, K.S. Park, I.D. Kim, ACS Nano 7 (2013) 7330. [67] Y.M. Sun, X.L. Hu, W. Luo, F.F. Xia, Y.H. Huang, Adv. Funct. Mater 23 (2013) 2436. [68] Y. Xiao, M.H. Cao, ACS Appl. Mater. Interfaces 7 (2015) 12840.