Preparation And Electrochemical Properties Of Nanostructured ZnAl-LDH Composite Materials For Ni-Zn Batteries

Abstract:The nickel-zinc rechargeable battery is an attractive power source for various electric appliances and large-scale energy storage systems due to its high specific energy, excellent specific power and high open-circuit voltage. Its battery performance is much than Ni-Cd and Ni-MH battery. However, the most critical problems of Ni-Zn rechargeable batteries are shape change and dendrite formation on the negative side resulting in poor cycling effciency, which limit their widespread commercialization. As is well known, the novel2D architecture of ZnAl-LDH can offer it to the replacement of conventional ZnO anode material in Ni-Zn secondary batteries. However, the practical implementation of ZnAl-LDH as an anode material for Ni-Zn batteries is hampered dramatically by its low intrinsic electrical conductivity. To alleviate this problem and further enhance the electrochemical performance of the ZnAl-LDH, one effective strategy is to design specific nanocomposites (carbon or metal), which could obviously increase the electrical conductivity of the ZnAl-LDH. The main points in this research can be summarized as following:(1) We adopt a new rapid method for the preparation of ZnAl-LDH nanoparticles. In our method, the ZnAl-LDH seeds separated from the mother liquor are re-dispersed in the deionized water and subsequently the ZnAl-LDH nanoparticles are developed at the crystal growth stage under hydrothermal conditions for24h. In contrast to the conventional co-precipitation method and conventional hydrothermal method, this simple process allows us to fabricate ZnAl-LDH nanosheets of high quality and purity. The ZnAl-LDH nanosheets prepared by our method represent a high crystallinity and a hexagonal plate-like structure. These features afford the ZnAl-LDH nanosheets much suitable for anode material in Ni-Zn battery application. (2) Nanostructured ZnAl-LDH/CNTs composite is successfully synthesized by a simple precipitation technique through the electrostatic interaction between positively charged layer of LDH and negatively charged functional groups on modified CNTs. The ZnAl-LDH/CNT composite with unique3D nanostructure is a novel nanomaterial which combines2D LDH nanosheet and ID carbon nanotubes together. The as-prepared LDH/CNT composite samples are used as anode materials for Ni-Zn battery, whose charge-discharge properties, electrochemical impedance spectroscopy and cycle performances are examined in detail. The results show that the improvement in the electrochemical properties is obtained.(3) Ag-coated ZnAl-LDH nanosheets are successfully prepared by a facile silver mirror reaction. The as-prepared Ag-coated ZnAl-LDH demonstrates high discharge capacity, good charge-discharge performance and excellent cycle stability. The EIS indicates that the Ag coating can remarkably decrease the charge-transfer resistance and improve the activity of anode material. This superior electrochemical performance is attributed to the anchored Ag coating which increases the electronic conductivity of anode.(4) The Ag/ZnAl-LDH composites with different Ag contents are fabricated. We investigate the effect of silver additive on the electrochemical performance of ZnAl-LDH. Structure and morphology analysis show that silver additive is dispersed on the surface of ZnAl-LDH nanosheets and the silver phases of composite samples with different Ag contents are not the same. When the silver content reaches to7.49wt.%(AL15), the uniform silver layer is formed. Electrochemical performances were evaluated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge tests. The AL15composite electrode has the highest reversible capacity (-406mAh g-1) than the others and the best cycling stability.(5) Surface decoration of ZnAl-LDH nanosheets with Ag nanoparticles is performed by a novel wet chemical method and no reducing agent is used. The electrochemical performance of the as-prepared Ag-LDH composites is significantly enhanced compared with the pure LDH nanosheets. The EIS measurement shows that the silver nanoparticles decrease the charge transfer resistance of Ag-LDH anodes by high conductive of Ag nanoparticles. Such intriguing electrochemical behavior is attributed to the conductive two-dimensional nanostructure with synergistic effects between a large specific surface area of LDH nanosheets and high conductivity of Ag nanoparticles.(6) GO/ZnAl-LDH composite is fabricated via the electrostatic interaction between positively ZnAl-LDH nanosheets and negatively charged graphene oxide. After hydrothermal reduction, the graphene/ZnAl-LDH composite is obtained. Such excellent electrochemical behavior is attributed to the synergistic effects between ZnAl-LDH nanosheets and high conductive graphene layers on the surface of LDH. The graphene/ZnAl-LDH shows outstanding cyclability, it is only decreased by?3%of the initial capacity at1C-rate even after1000charge-discharge cycles. Based on these observations, these newly designed3D graphene/ZnAl-LDH capsule may offer a promising anode active material for Ni-Zn secondary battery applications.