Facile synthesis of MOF-derived hollow NiO microspheres integrated with graphene foam for improved lithium-storage properties

Journal of Alloys and Compounds 784 (2019) 869e876

Contents lists available at ScienceDirect

Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom

Facile synthesis of MOF-derived hollow NiO microspheres integrated with graphene foam for improved lithium-storage properties Jinxiao Shao a, Hu Zhou a, **, Jianhui Feng b, Meizhou Zhu a, Aihua Yuan b, c, * a

School of Material Science and Engineering, Jiangsu University of Science and Technology, Zhenjiang, 212003, China School of Environmental and Chemical Engineering, Jiangsu University of Science and Technology, Zhenjiang, 212003, China c Marine Equipment and Technology Institute, Jiangsu University of Science and Technology, Zhenjiang, 212003, China b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 23 May 2018 Received in revised form 3 December 2018 Accepted 12 January 2019 Available online 14 January 2019

In this work, Ni-based metal-organic framework (MOF) hollow microspheres were firstly grown on the substrate of graphene foam (GF) by a facile solvothermal method, and then the NiO/GF composites were obtained after the calcination of Ni-MOF/GF precursors. The resulting NiO/GF could be employed as freestanding anode electrodes of lithium-ion batteries, showing superior specific capacities and cycling stabilities to pure NiO and GF. In detail, the optimized composite exhibited a capacity of 640 mAh g
1 after 50 cycles at 100 mA g
1. Even at a high current of 1 A g
1, the capacity still reached to ~330 mAh g
1. The excellent electrochemical performance can be attributed to the synergistic effect between NiO and GF components. The GF matrix not only improves the conductivity of electrode, but also provides a flexible platform for the loading of active materials, preventing the escape and diffusion of NiO particles into the electrolyte during the cycling. Meanwhile, the well-defined hierarchical hollow structure of NiO in the composite effectively mitigates the volume change of metal oxides during the insertion/extraction reaction. © 2019 Elsevier B.V. All rights reserved.

Keywords: Metal-organic framework Metal oxide Hollow Graphene foam Anode Lithium-ion batteries

1. Introduction Rechargeable lithium-ion batteries (LIBs) have attracted considerable interests of researchers in recent decades due to their applications in the field of energy source [1]. The development of electrodes has played a significant role, in which metal oxides were considered as ideal anode materials because of their high theoretical specific capacities [2]. Interestingly, hollow micro-/nanostructures have emerged as a key interest of research for energy conversion and storage, where the large interior space and specific surface area can provide sufficient contact between the electrode and electrolyte. More importantly, hollow-structured materials can effectively mitigate and alleviate the stress-induced structural variation associated with repeated insertion/extraction processes of lithium ions during long-term electrochemical reactions, thus leading to an improved cycling stability [3e8]. Recently, metal-

* Corresponding author. School of Environmental and Chemical Engineering, Jiangsu University of Science and Technology, Zhenjiang, 212003, China. ** Corresponding author. E-mail addresses: [email protected] (H. Zhou), [email protected] (A. Yuan). https://doi.org/10.1016/j.jallcom.2019.01.157 0925-8388/© 2019 Elsevier B.V. All rights reserved.

organic frameworks (MOFs) have been employed as suitable precursors to prepare metal oxides, which usually exhibited excellent electrochemical properties [9e11]. Unfortunately, the poor conductivity and large volume expansion of metal oxides in the charge/ discharge process greatly limited their practical applications. In the previous studies, it was an effective strategy to combine with carbonaceous materials to improve the conductivity of materials such as carbon fiber, carbon nanotube, carbon cloth, reduced graphene oxide, etc [12e21]. As we all know, graphene foam (GF) has a high conductivity, large specific surface area, flexible structure and strong mechanical property [22]. Numerous studies demonstrated that GF decorated with various active materials has been used directly as binder-free electrodes of high-performance rechargeable batteries and supercapacitors [23,24]. Thus, it can be predicted that the combination of MOF-derived hollow-structured metal oxides and the GF substrate would display outstanding lithium-storage properties. Our previous studies showed that MOF-derived needle-like Mn2O3 and octahedral CuO particles were successfully loaded on the surface of GF by a facile synthesis approach [25,26]. The obtained hierarchical composites can be employed as binder-free electrode materials of LIBs and supercapacitors, and have delivered excellent

870

J. Shao et al. / Journal of Alloys and Compounds 784 (2019) 869e876

electrochemical properties than pristine metal oxides in the gravimetric and areal capacities, rate performances and cycling stabilities. According to considerable literatures, it was proved that the structures and morphologies of metal oxides played crucial influences on the electrochemical properties [27]. Therefore, it is necessary to further explore the structure-property relationship involved in GF/MOF-derived metal oxides. Along this line, the NiO/GF composites with different NiO loadings were prepared in this contribution by using a two-step synthesis process. As shown in Scheme 1, hollow-structured NiMOF microspheres were firstly grown on the GF surface through a facile solvothermal method. Then, the NiO/GF composites were prepared after high-temperature treatment of Ni-MOF/GF. The obtained NiO/GF materials can be employed as binder-free anode materials, showing superior lithium-storage properties to pure NiO and GF. To the best of our knowledge, the present work gives the first example in introducing MOF-derived hollow structures into three-dimensional graphene such as GF or graphene aerogel applied in the field of LIBs. 2. Experimental details 2.1. Materials All chemicals were purchased with analytical grade from SigmaAldrich and used directly without further purification. The synthesis of graphene foam (GF) was referred to the literature method [28]. 2.2. Synthesis of Ni-MOF The Ni-MOF products were prepared by the procedure reported elsewhere with slight modifications [29]. Typically, Ni(NO3)2$6H2O (0.432 g), 1,3,5-benzenetricarboxylic acid (H3BTC) (0.15 g) and PVP (1.5 g) were dissolved in 30 mL of deionized water/ethanol/DMF (V/ V/V ¼ 1/1/1) mixture solvent under stirring. Then the solution was transferred into a Teflon-lined autoclave (50 mL) and kept in an oven at 150  C for 10 h. After the autoclave was cooled down to ambient temperature, the precipitates were collected by centrifugation, washed with deionized water and ethanol several times, and then dried at 60  C. Finally, the Ni-MOF products were harvested. 2.3. Synthesis of NiO The NiO products were prepared through the calcination of NiMOF precursors. Thermogravimetric (TG) analysis in air of Ni-MOF was carried out to determine the thermal stability and the

calcination temperature (Fig. S1a). An obvious loss of about 60% at 25e350  C corresponded to the gradual release of solvents and decomposition of organic ligands in the framework. Almost no further weight loss was observed over 350  C due to the formation of highly stable metal oxide (NiO). In detail, Ni-MOF crystals were firstly spread in a porcelain boat and subsequently placed in muffle furnace under air atmosphere. Then the temperature was raised from room temperature to 350  C with a heating rate of 1  C min
1, and kept at this temperature for 2 h. Upon cooling down naturally, the black NiO precipitates were obtained. 2.4. Synthesis of Ni-MOF/GF and NiO/GF The synthesis method of Ni-MOF/GF was similar to that of NiMOF except that a piece of GF (1 cm  1 cm, 0.80 mg) was added into the mixture solution during the preparation. It can be found that the color of GF changed from black to green, indicating the successful growth of Ni-MOF crystals on the GF surface. Accordingly, the NiO/GF composites were prepared through the calcination of Ni-MOF/GF precursors at 350  C. The color of bulk materials changed from green to black, confirming the complete conversion of Ni-MOF to NiO. In order to carry out the controlled experiments, three different NiO/GF composites were prepared by varying NiO mass loadings. The obtained products were named NiO-1/GF, NiO2/GF, and NiO-3/GF, respectively, with gradually increasing the NiO mass loading. TG analyses in air were conducted to determine the amount of carbon in the composite. As shown in Fig. S1b, the weight fractions of carbon in NiO-1/GF, NiO-2/GF, and NiO-3/GF were calculated to be approximately 48.4, 40.1, and 19.8 wt %, respectively. 2.5. Physical characterizations Powder X-ray diffraction (XRD) patterns were collected on a Shimadzu XRD-6000 diffractometer with Cu-Ka radiation. The structures and morphologies were observed by scanning electron microscopy (SEM, ZEISS Merlin Compact) and transmission electron microscopy (TEM, JEM-2100F). The elemental mapping distribution was investigated with an energy-dispersive X-ray spectrometry (EDS, Oxford X-Max). X-ray photoelectron spectroscopy (XPS) measurements were carried out on an ESCALAB 250 instrument (Thermo Electron) with Al-Ka radiation. TG analyses were conducted on Pyris Diamond TGA analyzer at a ramp rate of 5  C/min under air atmosphere. The nitrogen adsorptiondesorption isotherm was recorded at 77 K on a Quantachrome QuadraSorb Station 2 instrument. The sample was outgassed under vacuum at 373 K for 12 h prior to the adsorption measurement. The Brunauer-Emmett-Teller (BET) specific surface area was calculated

Scheme 1. The illustration of synthesis process for the NiO/GF integrated electrode material.

J. Shao et al. / Journal of Alloys and Compounds 784 (2019) 869e876

from the adsorption data, and the pore diameter distribution curve was determined using the Barrett-Joyner-Halenda (BJH) method. 2.6. Electrochemical measurements The GF and NiO/GF samples were applied directly as the working electrodes without any conductive and binding agents. The NiO anode was fabricated by mixing active material, acetylene black, and polyvinylidene fluoride (PVDF) binder in a weight ratio of 80:10:10 in N-methyl-2-pyrrolidone (NMP). The assembly of CR2032-type coin cells was performed in an Ar (O2 and H2O levels < 0.5 ppm)-filled glovebox with the anodes as-fabricated, metallic lithium cathode, Celgard 2300 film separator and 1 M LiPF6 in 1:1 ethylene carbonate (EC)/dimethyl carbonate (DEC) electrolyte. Galvanostatic charge/discharge curves were conducted by Land CT2001A battery testing system at various current densities in the voltage range of 0.01e3.0 V. Cyclic voltammetric (CV) curves were recorded on a computer-controlled CHI660D electrochemical workstation at a scan rate of 0.2 mV s
1. Electrochemical impedance spectroscopy (EIS) measurement was carried out with 5 mV amplitude in a frequency range from 0.1 Hz to 10 kHz at open circuit potential. 3. Results and discussion The structures of all samples were investigated by XRD, as depicted in Fig. 1. The diffraction patterns of pure Ni-MOF matched well with those reported in the literature [30]. For three Ni-MOF/GF composites, the characteristic peaks assigned to Ni-MOF were clearly observed, indicating the successful growth of Ni-MOF crystals on the GF substrate. Notably, the peak at 26.5 of GF overlapped with that of Ni-MOF in the composite. The peak of GF and the lattice planes of cubic NiO (JCPDS no. 78-0643) were also found in diffraction patterns of the NiO/GF sample, in which the peak at 2q ¼ 26.5 corresponded to the (002) lattice plane of graphitized carbon (JCPDS no. 75-1621). Furthermore, the diffraction intensity of GF in the composites became gradually weak upon increasing the NiO mass loading. Above results confirmed the complete conversion of Ni-MOF crystals on GF to NiO particles through a high temperature treatment. As shown in Fig. S2a, pure Ni-MOF exhibited well-defined hollow microspheres with average particle size of 1.4 mm. The morphology (Fig. S2b) of pristine NiO was similar to that of Ni-MOF, demonstrating that MOFs can be converted to the pre-designed metal oxides with controlled morphologies and sizes by a proper thermal treatment [31,32]. After the combination of both

871

components, the surface of GF was coated by Ni-MOF hollow microspheres (Fig. 2a, b, c). For the NiO/GF samples (Fig. 2d, e, 2f and Fig. S2), just a few NiO particles were scattered on the GF surface when the NiO content was lower (NiO-1/GF), while a large amount of NiO spheres significantly aggregated on GF for the NiO-3/GF sample with a much higher NiO loading. In comparison, NiO microspheres with an average particle size of 1.2 mm were densely and uniformly wrapped on the surface of GF when the NiO content was moderate (NiO-2/GF). Further observations showed that the crystalline needles were scattered on the outer surface of hollow NiO microsphere. The element mapping distribution of three NiO/GF composites revealed that C, Ni, and O elements were uniformly dispersed into the whole network of GF (Fig. S4), demonstrating the successful combination of NiO and GF components. TEM images further confirmed that NiO spheres in three NiO/GF composites had a hollow structure (Fig. 2, Fig. S3), which is consistent with SEM results. The SAED pattern of the NiO-2/GF sample exhibited a set of well-defined concentric rings, indicating the polycrystalline structure of NiO (Fig. 2g, inset). Such a hollow structure will alleviate the volume change during the charge/ discharge process, and promote the contact between electrolyte and active materials as well as provide more active sites [33]. The textural feature of pure NiO was investigated, as shown in Fig. S5. Pure NiO exhibited a typical type IV isotherm, where an approximately vertical rise of the curve at low-pressure region (P/P0~0) suggested the existence of micropores, while the distinct hysteresis loop in the P/P0 range of 0.41e0.99 indicated the presence of mesopores. The specific surface area and pore volume of NiO was measured to be 119 m2 g
1 and 0.213 cm3 g
1, respectively. So, it can be expected from the texture data of NiO that the hierarchically inter-connected and porous nanostructure of the NiO/GF composite will facilitate the mass diffusion of electrolyte and the fast transport of lithium ion as well as buffer the volume variation of NiO particles during the cycling. Only the XPS measurement of NiO-2/GF was investigated (Fig. 3), owing to the similar chemical composition and element valence for three composites. The XPS survey of NiO-2/GF confirmed the presence of C, Ni and O species. The peak at around 284.8 eV in the high-resolution C 1s spectrum originated from the sp2 hybridized C of GF. The two major characteristic peaks at 854.2 and 873.0 eV in the Ni 2p spectrum (Fig. 2c) were assigned to Ni 2p3/2 and Ni 2p1/2 spin orbits, respectively, which matched with the reported data [34]. In addition, the satellite peaks of Ni 2p3/2 and Ni 2p1/2 were observed at 861.2 and 879.9 eV, respectively. The O1s spectrum is composed of two Gaussian peaks with the binding energies of 529.8 and 531.7 eV for C]O and C-O,

Fig. 1. XRD patterns of the (a) Ni-MOF/GF and (b) NiO/GF composites.

872

J. Shao et al. / Journal of Alloys and Compounds 784 (2019) 869e876

Fig. 2. SEM images of (a,b,c) Ni-MOF-2/GF and (d,e,f) NiO-2/GF, (g) TEM image of NiO-2/GF (Inset: the corresponding SAED pattern of NiO), (h) elemental mapping distribution of NiO in NiO-2/GF.

Fig. 3. XPS spectra of NiO-2/GF: (a) survey, (b) C 1s, (c) Ni 2p, and (d) O 1s.

respectively. The XPS result demonstrated the successful conversion of Ni-MOF/GF to NiO/GF after the calcination treatment.

CV curves of the first three cycles for the NiO-2/GF electrode in a voltage range of 0.01e3.0 V at a scan rate of 0.2 mV s
1 were shown

J. Shao et al. / Journal of Alloys and Compounds 784 (2019) 869e876

in Fig. 4a. During the first cathode scan, several distinct peaks were observed due to the multi-step electrochemical reaction. The peak at about 0.9 V was attributed to the generation of Li2O, whereas the peak at 0.4 V corresponded to some irreversible reactions such as the formation of SEI film and decomposition of Ni2O to Ni. In addition, the weak peak below 0.5 V was related to the lithium insertion/extraction process of GF [35]. In the second cycle, the position and intensity of anode peak remained unchanged. During the anodic reaction, two peaks at around 1.4 and 2.2 V were related to the decomposition of the SEI membrane and the oxidation of Ni to NiO via Ni2O, respectively [36]. The entire electrode reaction process can be summarized as the formula: NiO þ 2Liþ þ 2e
4 Ni þ Li2O. The third lap curve basically overlaped with the second one, indicating that the electrode has a good redox reversibility [37]. Fig. 4b showed the charge/discharge curves of NiO-2/GF in the voltage range of 0.01e3.0 V at 100 mA g
1. The charge and discharge capacities at the first cycle were 612 and 903 mAh g
1, respectively, with an initial coulombic efficiency of 67.8%. The serious capacity decay may be ascribed to the irreversible reactions such as the intercalation of graphene sheets, the formation of solid electrolyte membrane as well as the decomposition of electrolyte on the electrode surface [38]. The high coulombic efficiency of the electrode exceeded 95% from the second cycle. The curves of the 2nd and 3rd laps were almost overlapped, indicating a high cycling stability of the composite electrode. The charge and discharge capacities of the 50th cycle were 625 and 640 mAh g
1, respectively, with a high coulombic efficiency of 97.7%. The proposed electron transfer and the Liþ diffusion mechanism for the NiO/GF composite system was outlined in Fig. 4c. During the initial lithiation-delithiation process, metallic Ni particles and Li2O form upon the irreversible reaction between Liþ and NiO. Subsequently, these Ni particles reversibly react with Li2O to form NiO and Liþ. In this process, the GF substrate has a high structural stability and also provides 3D conductive electron paths, ensuring the excellent electronic conductivity of integral electrode. The cycling performances of NiO, GF and NiO/GF were measured at 100 mA g
1 (Fig. 5a). Among these materials, the coulomb

873

efficiency of NiO-2/GF was just 67.8% at the first cycle, because of the irreversible reaction and the formation of SEI. In the second cycle, the specific capacity decreased from the initial 903 mAh g
1 to 628 mAh g
1, and remained almost unchanged in the next 50 cycles. The NiO-2/GF composite has a specific capacity of 640 mAh g
1 after 50 cycles, comparable with those of 424 and 232 mAh g
1 observed in NiO-1/GF and Ni-3/GF, respectively. Different from the composites, pure NiO displayed a continuous and significant capacity decay from the first cycle, and only delivered a specific capacity of 66 mAh g
1 after 50 cycles. The charge/discharge curves of NiO and NiO-2/GF were carried out at different current densities to investigate the rate performance (Fig. 5b). The specific capacities of NiO-2/GF were around 635, 545, 430, 340 and 210 mAh g
1 at 100, 200, 500, 1000 and 2000 mA g
1, respectively. In contrast, the specific capacities of pure NiO decreased dramatically and were close to zero at high current densities. Clearly, the rate capacity of NiO-2/GF was much better than that of NiO after the incorporation of conductive GF substrate. On the basis of above results, the high capacity and superior stability of the NiO/GF composites to GF and NiO can be attributed to the strong synergistic interaction between GF and NiO components as follows: First, the introduction of conductive GF can serve as an effective elastic buffer to relieve the volume variation and accelerate the electron transfer process, improving the cycle stability and rate capability of integrated electrode. Second, the hollow structure can not only alleviate the volume change of NiO particles but also shorten the diffusion path of lithium ions. Third, the elastic GF substrate can effectively hinder the aggregation of NiO particles, and simultaneously the large interfacial area can provide more storage sites for lithium ions. Due to the combination effect of these factors, the NiO/GF composites show better electrochemical performances than GF and NiO. In order to perform the controlled experiments, the influence of NiO mass loading in the NiO/GF composites were further examined (Fig. 5c). It is observed that much lower or higher mass loadings of NiO in the composites resulted in worse electrochemical properties. The poor capacity for the NiO-1/GF sample was related to the low

Fig. 4. (a) CV curves of NiO-2/GF measured at a scan rate of 0.2 mV s
1 in the voltage range of 0.01e3.0 V (vs. Li/Liþ), (b) Charge-discharge curves of NiO-2/GF at 100 mA g
1, (c) Schematic illustration of the lithiation-delithiation process of the NiO/GF composite system.

874

J. Shao et al. / Journal of Alloys and Compounds 784 (2019) 869e876

Fig. 5. (a) Cycling performances and coulombic efficiency at 100 mA g
1 of NiO, GF, and NiO-2/GF, (b) Rate performances of NiO and NiO-2/GF, (c) Cycling performances of NiO/GF with different NiO loadings, (d) Nyquist plots of NiO and NiO/GF (Inset: the simplified equivalent circuit of the electrode material before cycles).

NiO loading, in which NiO mainly provides the capacity contribution of electrode. In contrast, the low capacity for the NiO-3/GF sample can be attributed to the much higher content of NiO, which decrease of the conductivity for electrode. In addition, the excessively NiO particles weaken the attachment between NiO and GF components, resulting in the escape and diffusion of partial NiO particles into the electrolyte during the cycles and thus to a continuous decrease in cycling stability. So, the mass loading of NiO should be finely controlled to achieve the optimum result, and a moderate loading will facilitate the achievement of the best lithium storage performance. In spite of these factors, both NiO-1/GF and NiO-3/GF composites still displayed better electrochemical properties than pure NiO and GF. Similar phenomena have been also found in those carbon-based materials [39e41]. The lithium-storage properties of the NiO-2/GF sample can be comparable with those reported NiObased anode materials as listed in Table 1 [42e49]. The Nyquist plots of pure NiO and the NiO/GF electrodes were shown in Fig. 5d. The fitting values with Zview software of the resistance components in the simplified equivalent circuit were given in Table S1. Re is the lithium-ion diffusion resistance in the

electrolyte, while the depressed semicircle in the high frequency region presents the charge transfer resistance of the material (Rct). CPE and Zw are the constant phase element and the Warburg impedance, respectively. It can be obviously seen that the Rct values of three composites are much smaller than those observed for pure NiO. The analysis from EIS indicates that the introduction of GF effectively improves the lithium-ion diffusion and charge transfer process during the Liþ insertion/extraction reaction, resulting in an excellent cycle stability. In addition, the Rct values for the composites are issued in the following order: NiO-3/GF > NiO-2/ GF > NiO-1/GF. After 50 cycles, the curve radius of NiO-2/GF was significantly reduced (Fig. S6), indicating the resistance of electrode became smaller. SEM image of NiO after the cycles revealed that the structure of hollow NiO microspheres collapsed severely, resulting in an obvious capacity decay (Fig. 6). In contrast, the NiO-2/GF electrode remained intact free-standing framework, where hollow NiO microspheres were well preserved and still uniformly coated on the surface of GF, revealing the tight attachment between NiO particles and GF, and facilitated the improvement of cycle stability.

Table 1 Comparison of the lithium-storage properties for the NiO-2/GF composite with related NiO-based materials. Electrode materials

Current density (mA g
1)

Capacity (mAh g
1)

Reference

NiO-2/GF NiO@C/pRGO NiO@CMK Egg shell-yolk NiO/C NiO/C@CNT NiO/graphene NiO/C Ni-NiO/CNT NiO/N-doped graphene

100 200 400 100 50 200 70 200 80

640 (50 cycles) 1003 (200 cycles) 848 (50 cycles) 625 (100 cycles) 573 (20 cycles) 262 (100 cycles) 586 (50 cycles) 736 (50 cycles) 1105 (150 cycles)

This work [23] [24] [25] [26] [27] [28] [29] [30]

J. Shao et al. / Journal of Alloys and Compounds 784 (2019) 869e876

875

Fig. 6. SEM images of (a, b) NiO and (c, d) NiO-2/GF after 50 cycles.

4. Conclusions In summary, a facile synthesis strategy was applied to fabricate the NiO/GF composites by using Ni-MOF as precursor and GF as substrate. The as-prepared self-standing NiO/GF composites were directly employed as the integrated electrodes of LIBs. The flexible GF matrix and hollow-structured NiO microspheres effectively increased the specific capacity and cycling stability of electrode. The optimized NiO-2/GF composite with moderate NiO mass loading delivered the highest lithium-storage property due to the synergistic effect between NiO and GF components. The present contribution demonstrated that the NiO/GF composite can be used as excellent anode materials applied in high-performance LIBs.

[6]

[7]

[8]

[9]

[10]

Acknowledgments [11]

This work was financially supported by the National Natural Science Foundation of China (51672114), Natural Science Foundation of Jiangsu Province, China (BK20151328, BK20161357), Foundation from Marine Equipment and Technology Institute for Jiangsu University of Science and Technology, China (HZ20180004), and the project of the Priority Academic Program Development of Jiangsu Higher Education Institutions, China.

[12]

[13]

[14]

Appendix A. Supplementary data

[15]

Supplementary data to this article can be found online at https://doi.org/10.1016/j.jallcom.2019.01.157.

[16]

References

[17]

[1] J.W. Choi, D. Aurbach, Promise and reality of post-lithium-ion batteries with high energy densities, Nat. Rev. Mater. 1 (2016) 16013. [2] J. Mei, T. Liao, L.Z. Kou, Z.Q. Sun, Two-dimensional metal oxide nanomaterials for next-generation rechargeable batteries, Adv. Mater. 29 (2017), 1700176. [3] G. Zhang, X.W. Lou, General synthesis of multi-shelled mixed metal oxide hollow spheres with superior lithium storage properties, Angew. Chem. Int. Ed. 53 (2014) 9041e9044. [4] J. Liu, H. Xia, D.F. Xue, L. Lu, Double-shelled nanocapsules of V2O5-based composites as high-performance anode and cathode materials for Li ion batteries, J. Am. Chem. Soc. 131 (2009) 12086e12087. [5] W.M. Zhang, J.S. Hu, Y.G. Guo, S.F. Zheng, L.S. Zhong, W.G. Song, L.J. Wan, Tin-

[18]

[19]

[20]

nanoparticles encapsulated in elastic hollow carbon spheres for highperformance anode material in lithium-ion batteries, Adv. Mater. 20 (2008) 1160e1165. X.W. Hu, S. Liu, B.T. Qu, X.Z. You, Starfish-shaped Co3O4/ZnFe2O4 Hollow nanocomposite: synthesis, supercapacity, and magnetic properties, ACS Appl. Mater. Interfaces 7 (2015) 9972e9981. J. Wang, N. Yang, H. Tang, Z. Dong, Q. Jin, M. Yang, D. Kisailus, H. Zhao, Z. Tang, D. Wang, Accurate control of multishelled Co3O4 hollow microspheres as high-performance anode materials in lithium-ion batteries, Angew. Chem. Int. Ed. 52 (2013) 6417e6420. H. Tabassum, R.Q. Zou, A. Mahmood, Z.B. Liang, Q.F. Wang, H. Zhang, S. Gao, C. Qu, W.H. Guo, S.J. Guo, A universal strategy for hollow metal oxide nanoparticles encapsulated into B/N Co-doped graphitic nanotubes as highperformance lithium-Ion battery anodes, Adv. Mater. 30 (2018), 1705441. W. Xia, A. Mahmood, R.Q. Zou, Q. Xu, Metal-organic frameworks and their derived nanostructures for electrochemical energy storage and conversion, Energy Environ. Sci. 8 (2015) 1837e1866. J.H. Zhang, M. Huang, B.J. Xi, K. Mi, A.H. Yuan, S.L. Xiong, Systematic study of effect on enhancing specific capacity and electrochemical behaviors of lithium-sulfur batteries, Adv. Energy Mater. 8 (2018), 1701330. J.H. Feng, H. Zhou, J.P. Wang, T. Bian, J.X. Shao, A.H. Yuan, MoS2 supported on MOF-derived carbon with core-shell structure as efficient electrocatalysts for hydrogen evolution reaction, Int. J. Hydrogen Energy 43 (2018) 20538e20545. W. Xue, Q.-B. Yan, G. Xu, L. Suo, Y. Chen, C. Wang, C.-A. Wang, J. Li, Doubleoxide sulfur host for advanced lithium-sulfur batteries, Nano Energy 38 (2017) 12e18. X. Li, Y. Chen, H. Huang, Y.-W. Mai, L. Zhou, Electrospun carbon-based nanostructured electrodes for advanced energy storage - a review, Energy Storage Mater. 5 (2016) 58e92. Y. Chen, J. Dong, L. Qiu, X. Li, Q. Li, H. Wang, S. Liang, H. Yao, H. Huang, H. Gao, J.-K. Kim, F. Ding, L. Zhou, A catalytic etching-wetting-dewetting mechanism in the formation of hollow graphitic carbon fiber, Chem 2 (2017) 299e310. Y. Chen, X. Li, K. Park, W. Lu, C. Wang, W. Xue, F. Yang, J. Zhou, L. Suo, T. Lin, H. Huang, J. Li, J.B. Goodenough, Nitrogen-doped carbon for sodium-ion battery anode by self-etching and graphitization of bimetallic MOF-based composite, Chem 3 (2017) 152e163. Y.M. Chen, X.Y. Li, K. Park, L.M. Zhou, H.T. Huang, Y.-W. Mai, J.B. Goodenough, Hollow nanotubes of N-doped carbon on CoS, Angew. Chem. Int. Ed. 55 (2016) 15831e15834. G. Huang, F.F. Zhang, X.C. Du, Y.L. Qin, D.M. Yin, L.M. Wang, Metal organic frameworks route to in situ insertion of multiwalled carbon nanotubes in Co3O4 polyhedra as anode materials for lithium-ion batteries, ACS Nano 9 (2015) 1592e1599. G. Zhang, S. Hou, H. Zhang, W. Zeng, F. Yan, C.C. Li, H. Duan, High-performance and ultra-stable lithium-ion batteries based on MOF-derived ZnO@ZnO quantum dots/C core-shell nanorod arrays on a carbon cloth anode, Adv. Mater. 27 (2015) 2400e2405. Z.G. Zang, X.F. Zeng, M. Wang, W. Hu, C.R. Liu, X.S. Tang, Tunable photoluminescence of water-soluble AgInZnS-graphene oxide (GO) nanocomposites and their application in-vivo bioimaging, Sens. Actuators B Chem. 252 (2017) 1179e1186. X.M. Liu, T. Xu, Y.L. Li, Z.G. Zang, X.S. Peng, H.Y. Wei, F. Wang, Enhanced X-ray

876

[21]

[22]

[23]

[24]

[25]

[26]

[27]

[28]

[29]

[30]

[31] [32]

[33]

[34]

[35]

J. Shao et al. / Journal of Alloys and Compounds 784 (2019) 869e876 photon response in solution-synthesized CsPbBr3 nanoparticles wrapped by reduced graphene oxide, Sol. Energy Mater. Sol. Cells 187 (2018) 249e254. J. Wei, Z.G. Zang, Y.B. Zhang, M. Wang, J. Du, X.S. Tang, Enhanced performance of light-controlled conductive switching in hybrid cuprous oxide/reduced graphene oxide (Cu2O/rGO) nanocomposites, Opt. Lett. 42 (2017) 911e914. X.H. Cao, Z.Y. Yin, H. Zhang, Three-dimensional graphene materials: preparation, structures and application in supercapacitors, Energy Environ. Sci. 7 (2014) 1850e1865. Z.Q. Yan, W.L. Yao, L. Hu, D.D. Liu, C.D. Wang, C.S. Lee, Progress in the preparation and application of three-dimensional graphene-based porous nanocomposites, Nanoscale 7 (2015) 5563e5577. M.Z. Zhu, H. Zhou, J.X. Shao, J.H. Feng, A.H. Yuan, Prussian blue nanocubes supported on graphene foam as superior binder-free anode of lithium-ion batteries, J. Alloys Compd. 749 (2018) 811e817. D. Ji, H. Zhou, J. Zhang, Y.Y. Dan, H.X. Yang, A.H. Yuan, Facile synthesis of metal-organic framework-derived Mn2O3 nanowires coated threedimensional graphene network for high performance free-standing supercapacitor electrodes, J. Mater. Chem. A 4 (2016) 8283e8290. D. Ji, H. Zhou, Y.L. Tong, J.P. Wang, M.Z. Zhu, T.H. Chen, A.H. Yuan, Facile fabrication of MOF-derived octahedral CuO wrapped 3D graphene network as binder-free anode for high performance lithium-ion batteries, Chem. Eng. J. 313 (2017) 1623e1632. J. Jiang, Y.Y. Li, J.P. Liu, X.T. huang, C.Z. Yuan, X.W. Lou, Recent advances in metal oxide-based electrode architecture design for electrochemical energy storage, Adv. Mater. 24 (2012) 5166e5180. X.H. Cao, Y.M. Shi, W.H. Shi, G. Lu, X. Huang, Q.Y. Yan, Q.C. Zhang, H. Zhang, Preparation of novel 3D graphene networks for supercapacitor applications, Small 7 (2011) 3163e3168. F. Zou, Y.M. Chen, K.W. Liu, Z.T. Yu, W.F. Liang, S. Bhaway, M. Gao, Y. Zhu, Metal organic frameworks derived hierarchical hollow NiO/Ni/graphene composites for lithium and sodium storage, ACS Nano 10 (2016) 377e386. O.M. Yaghi, H. Li, T.L. Groy, Construction of porous solids from hydrogenbonded metal complexes of 1,3,5-benzenetricarboxylic acid, J. Am. Chem. Soc. 118 (1996) 9096e9101. S. Dang, Q.L. Zhu, Q. Xu, Nanomaterials derived from metal-organic frameworks, Nat. Rev. Mater. 3 (2017) 17075. J.P. Wang, H. Zhou, M.Z. Zhu, A.H. Yuan, X.P. Shen, Metal-organic frameworkderived Co3O4 covered by MoS2 nanosheets for high-performance lithium-ion batteries, J. Alloys Compd. 744 (2018) 220e227. M.X. Liu, X. Wang, D.Z. Zhu, L.C. Li, H. Duan, Z.J. Xu, Z.W. Wang, L.H. Gan, Encapsulation of NiO nanoparticles in mesoporous carbon nanospheres for advanced energy storage, Chem. Eng. J. 308 (2017) 240e247. N.B. Trung, T.V. Tam, D.K. Dang, K.F. Babu, E.J. Kim, J. Kim, W.M. Choi, Facile synthesis of three-dimensional graphene/nickel oxide nanoparticles composites for high performance supercapacitor electrode, Chem. Eng. J. 264 (2015) 603e609. W.X. Guo, W.W. Sun, Y. Wang, Multilayer CuO@NiO hollow spheres: microwave-assisted metal-organic-framework derivation and highly

[36]

[37]

[38]

[39]

[40]

[41]

[42]

[43]

[44]

[45]

[46]

[47]

[48]

[49]

reversible structure-matched stepwise lithium storage, ACS Nano 9 (2015) 11462e11471. X.H. Huang, J.P. Tu, X.H. Xia, X.L. Wang, J.Y. Xiang, Nickel foam-supported porous NiO/polyaniline film as anode for lithium ion batteries, Electrochem. Commun. 10 (2008) 1288e1290. Y.Y. Zheng, Y.W. Li, J.H. Yao, Y. Huang, S.H. Xiao, Facile synthesis of porous tubular NiO with considerable pseudocapacitance as high capacity and long life anode for lithium-ion batteries, Ceram. Int. 44 (2018) 2568e2577. C. Li, T.Q. Chen, W.J. Xu, X.B. Lou, L.K. Lou, Q. Chen, B.W. Hu, Mesoporous nanostructured Co3O4 derived from MOF template: a high-performance anode material for lithium batteries, J. Mater. Chem. A 3 (2015) 5585e5591. T. Jiang, F. Bu, X. Feng, I. Shakir, G. Hao, Y. Xu, Porous Fe2O3 nanoframeworks encapsulated within three-dimensional graphene as high-performance flexible anode for lithium-ion battery, ACS Nano 11 (2017) 5140e5147. W. Sun, Z. Hu, C. Wang, Z. Tao, S.L. Chou, Y.M. Kang, H.K. Liu, Effects of carbon content on the electrochemical performances of MoS2-C nanocomposites for Li-ion batteries, ACS Appl. Mater. Interfaces 8 (2016) 22168e22174. Y. Xu, S. Hou, G. Yang, T. Lu, L. Pan, NiO/CNTs derived from metal-organic frameworks as superior anode material for lithium-ion batteries, J. Solid State Electrochem. 22 (2017) 785e795. C.Y. Ding, W.W. Zhou, X.Y. Wang, B. Shi, D. Wang, P.Y. Zhou, G.W. Wen, Hybrid aerogel-derived carbon/porous reduced graphene oxide dual-functionalized NiO for high-performance lithium storage, Chem. Eng. J. 332 (2018) 479e485. Z.Y. Fan, J. Liang, W. Yu, S.J. Ding, S.D. Cheng, G. Yang, Y.L. Wang, Y.X. Xi, K. Xi, R.V. Kumar, Ultrathin NiO nanosheets anchored on a highly ordered nanostructured carbon as an enhanced anode material for lithium ion batteries, Nano Energy 16 (2015) 152e162. G.M. Li, Y. Li, J. Chen, P.P. Zhao, D.G. Li, Y.H. Dong, L.P. Zhang, Synthesis and research of egg shell-yolk NiO/C porous composites as lithium-ion battery anode material, Electrochim. Acta 245 (2017) 941e948. J.P. Zhou, H.Y. Mi, J.D. Wang, Q.X. Cui, J.L. Zhong, Preparation and lithium storage performance of NiO/C@CNT anode material, Rare Metal Mater. Eng. 44 (2015) 2109e2113. L.H. Chu, M.C. Li, Y. Wang, X.D. Li, Z.P. Wan, S.Y. Dou, Y. Chu, Multishelled NiO hollow spheres decorated by graphene nanosheets as anodes for lithium-ion batteries with improved reversible capacity and cycling stability, J. Nanomater. 2016 (2016) 1e6. L.P. Zhang, J.C. Mu, Z. Wang, G.M. Li, Y.L. Zhang, Y.H. He, One-pot synthesis of NiO/C composite nanoparticles as anode materials for lithium-ion batteries, J. Alloys Compd. 671 (2016) 60e65. I. Elizabeth, A.K. Nair, B.P. Singh, S. Gopukumar, Multifunctional Ni-NiO-CNT composite as high performing free standing anode for Li Ion batteries and advanced electro catalyst for oxygen evolution reaction, Electrochim. Acta 230 (2017) 98e105. J.Y. Chen, X.F. Wu, Y. Liu, Y. Gong, P.F. Wang, W.H. Li, S.P. Mo, Q.Q. Tan, Y.F. Chen, Hierarchically-structured hollow NiO nanospheres/nitrogen-doped graphene hybrid with superior capacity retention and enhanced rate capability for lithium-ion batteries, Appl. Surf. Sci. 425 (2017) 461e469.