Shape-controlled growth of three-dimensional flower-like ZnO@Ag composite and its outstanding electrochemical performance for Ni-Zn secondary batteries

https://doi.org/10.1016/j.jcis.2019.11.083Get rights and content

Abstract

A novel three-dimensional (3D) flower-like ZnO@Ag composite is successfully synthesized through a simple and facile process, which is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS).When evaluated as an anodic material for nickel-zinc alkaline secondary batteries, the 3D flower-like ZnO@Ag composite exhibits the high discharge capacity (627 mAh g−1) and long cycle life (830 cycles). The outstanding electrochemical performance is ascribed to the Ag nanoparticles enhancing electron conductivity and the uniform flower-like structure providing enough electrochemical reaction sites, so as to reduce electrode polarization and improve cell efficiency. Furthermore, the possible growth mechanism of 3D flower-like ZnO@Ag composite has been proposed. The effect of silver content on formation of ZnO@Ag composites was also investigated in detail, indicating the appropriate silver content plays a key role in forming a defined 3 D flower-like structure for the ZnO@Ag composite.

Introduction

With the increasing energy demand for the rapid development of economy and society, the consumption of conventional energies such as the coal, crude oil and other fossil fuels is increasing dramatically, causing severe environmental pollution and the sharp declines in their reserves [1], [2], [3]. In order to solve the energy crisis and environmental pressure, the exploitation of renewable and green energy sources such as wind energy, solar energy and tidal energy has received more and more attention from all over the world [4], [5], [6]. The energy conversion and storage systems such as fuel-cells, batteries and super-capacitors are the key components for enabling these renewable energy sources into the electrical grid [7], [8], [9], [10], [11], [12], [13], [14], [15]. Among them, the rechargeable aqueous Nickel/Zinc (Ni-Zn) battery is considered one of the most promising candidates for energy storage, due to its advantages such as high specific power density, smooth discharge platform, security, low cost and environment friendliness [16], [17], [18], [19]. However, the poor cycle life of Ni-Zn battery has seriously restrained its large-scale application and development. The main cause is the high dissolution and non-uniform deposition of zinc species during the repeated charge-discharge process, resulting in the shape change of electrode and zinc dendrite growth [20], [21], [22], [23]. In the worst situation, the growing zinc dendrite can penetrate the separator to cause the short circuit of battery system.

Up to now, a great deal of effort has been taken to conquer these troubles [24], [25], [26], [27]. Among the various approaches, the metallic silver decoration on the surface of anode materials have been considered as an effective method to improve the electrochemical performance of electrodes in various batteries [28], [29], [30], [31]. It is attributed to that metallic silver is an excellent electric conductor, which can enormously increase the electronic conductivity of the active materials, resulting in faster electron transportation on the electrode. In addition, the metallic silver decorated on the surface of active materials may obstruct the direct contact of the active materials with the electrolyte, leading to that the dissolution of active materials can be inhibited effectively. In previous reports, Wu et al. coated silver particles on the surface of conventional ZnO by silver mirror reaction. The Ag-coated ZnO exhibited the better electrochemical performance than that of uncoated ZnO, maintaining the discharge specific capacity at 456 mAh g−1 throughout 65 cycles [32]. Huang et al. prepared a ZnO/Ag/polypyrrole composite by using a silver ammonia complex ion as the oxidizing agent and a pyrrole monomer as the reducing agent, exhibiting a much higher capacity retention of about 82% than that of the pristine ZnO electrode (about 43%) after 100 cycles [33]. However, these silver-modified conventional ZnO are one-dimensional (1D) materials, presenting a hexagonal prism morphology that has relatively low specific surface area. It can only provide limited contact area with the electrolyte, so as to restrict the utilization of active materials and reduce the cycle life. What’s more, the morphology of active materials will have a great influence on both the dendrite growth and shape change of zinc electrode during cycle process [34], [35], [36]. Yang et al. reported that silver nanoparticles deposited two-dimensional (2D) Zn-Al layered double hydroxide sheets (Ag-LDH composite) displayed an excellent cycling stability [37]. Nevertheless, its discharge capacity was lower than that of Ag-coated ZnO, due to that the theoretical capacity (420 mA h g−1) of Zn-Al-LDH is much lower than that of ZnO (659 mA h g−1). So, it is desirable to develop a material that integrating the good electrical conductivity of Ag nanoparticles and the perfect morphology of ZnO, which would exhibit considerable electrochemical properties for Ni-Zn secondary batteries.

Up to now, there are few reports about silver optimizing ZnO structure while decorating on its surface. Thus, in the present work, a novel three-dimensional (3D) flower-like Ag@ZnO composite was successfully synthesized through the facile process with a self-assembly route, which ingeniously combines the advantages of metallic silver and unique 3D flower-like architecture. As we know, beside the good electrical conductivity, metallic silver has high hydrogen evolution overpotential to inhibit hydrogen evolution during charge process of battery, which would reduce electrode polarization and improve cell efficiency. On the other hand, the uniform flower-like structure has a stable framework and a larger specific surface area than other morphologies of ZnO, which would provide sufficient electrochemical active sites and optimize zinc electro-deposition orientation. Compared to previous studies, the 3D flower-like Ag@ZnO composite showed the high discharge capacity (627 mAh g−1) and long cycle life (830 cycles), demonstrating it is a promising candidate as an anodic material for Ni-Zn secondary batteries. Moreover, the formation mechanism of the 3 D flower-like ZnO@Ag composite was proposed in this paper, demonstrating that the silver content had strong effect on the formation of ZnO nanosheets and self-assembly flower-like morphology.

Section snippets

The preparation of materials

The 3 D flower-like ZnO@Ag composites was prepared by a facile procedure. Firstly, 6 mmol of zinc nitrate hexahydrate (Zn(NO3)2·6H2O), 15 mmol of trisodium citrate (Na3C6H5O7·2H2O) and a certain amount of silver nitrate (AgNO3) were dissolved into 150 mL of a mixed solvent containing distilled water and ethanol with volume ratio of 1: 2. Afterward, 10 mL of NaOH aqueous solution (3 M) was slowly dropped into the above mixed solution under violently stirring for about 30 min at room temperature

Materials characterization

Fig. 1 shows the XRD patterns of pure ZnO microsphere and the 3 D flower-like ZnO@Ag composites. The diffraction peaks, located at 31.7˚, 34.3˚, 36.2˚, 47.4˚, 56.5˚, 62.8˚ and 67.8˚, can be observed in the XRD patterns of all the samples, which correspond to the (1 0 0), (0 0 2), (1 0 1), (1 0 2), (1 1 0), (1 0 3) and (1 1 2) crystal planes of hexagonal wurtzite ZnO (JCPDS NO. 36-1451). However, the peaks appearing at 38˚ and 44˚ can be only found in the XRD patterns of ZnO@Ag composites (FZA5,

Conclusions

In this work, the regular 3D flower-like ZnO@Ag composite self-assembled by nanosheets was successfully synthesized by a facile one-pot method with the assistance of ethanol and citrate. Most interestingly, the SEM images reveal the different morphology and structure for the Ag-free ZnO microspheres and ZnO@Ag composites, demonstrating that the appropriate Ag content plays a crucial role in the formation of 3D flower-like ZnO@Ag composite. It may be ascribed to that the Ag nanoparticles

Declaration of Competing Interest

We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. 21371180) and Hunan Provincial Science and Technology Plan Project (No. 2017TP1001).

References (48)

  • L. Wang et al.

    Formation of porous ZnO microspheres and its application as anode material with superior cycle stability in zinc-nickel secondary batteries

    J. Power Sources

    (2018)
  • L. Liu et al.

    Improved performance of flower-like ZnAl LDH growing on carbon nanotubes used in zincenickel secondary battery

    Electrochim. Acta

    (2018)
  • F. Cui et al.

    Preparation of a peony-liked 3-D hydrotalcite and its electrochemical performance as a zinc negative electrode

    Mater. Res. Bull.

    (2019)
  • L. Wang et al.

    Mesoporous yolk-shell ZnO/C microspheres as active ingredient of zinc anode with outstanding cycle stability and high rate performance

    J. Alloys Compd.

    (2019)
  • L. Hu et al.

    Micro/nano-structured Ag coated VPO4/C as a high-performance anode material for lithium-ion batteries

    Mater. Lett.

    (2019)
  • W. Guo et al.

    MOFs derived Ag/ZnO nanocomposites anode for Zn/Ni batteries

    J. Solid State Chem.

    (2019)
  • X. Lu et al.

    3D Ag/NiO-Fe2O3/Ag nanomembranes as carbon-free cathode materials for Li-O2 batteries

    Energy Storage Mater.

    (2019)
  • Y. Cao et al.

    Synthesis of Ag/Co@CoO NPs anchored within N-doped hierarchical porous hollow carbon nanofibers as a superior free-standing cathode for Li-O2 batteries

    Carbon

    (2019)
  • J.Z. Wu et al.

    Ag-modification improving the electrochemical performance of ZnO anode for Ni/Zn secondary batteries

    J. Alloys Compd.

    (2009)
  • R. Wen et al.

    Electrochemical performances of ZnO with different morphology as anodic materials for Ni/Zn secondary batteries

    Electrochim. Acta

    (2012)
  • V. Caldeira et al.

    Controlling the shape change and dendritic growth in Zn negative electrodes for application in Zn/Ni batteries

    J. Power Sources

    (2017)
  • S. Koppala et al.

    Hierarchical ZnO/Ag nanocomposites for plasmon-enhanced visible-light photocatalytic performance

    Ceram. Int.

    (2019)
  • H. Liu et al.

    Synthesis of spherical Ag/ZnO heterostructural composites with excellent photocatalytic activity under visible light and UV irradiation

    Appl. Surf. Sci.

    (2015)
  • Z. Zhao et al.

    Synergistic effect of ZnO@Bi/C sphere for rechargeable Zn-Ni battery with high specific capacity

    J. Power Sources

    (2019)
  • Cited by (33)

    View all citing articles on Scopus
    View full text