Construction Of Nickel-based Layered Double Hydroxides Nanoarrays For Aqueous Electrochemical Energy Storage

Nowadays,the world's energy requirements are mainly supplied by the combustion of fossil fuels,which have promoted ecological problems and lasting effects on the global economy and society.There is an urgent demand for efficient,eco-friendly and cost-effective energy storage devices that can meet energy requirements of various fields.High-performance,environmentally friendly,low-cost and safe supercapacitors and batteries are becoming more and more important for portable electronics and electric vehicles to meet the energy requirements.Transition metal layer double hydroxides(LDH)material,as a representative of layered materials,has become a research hotspot in recent years,because of its high specific capacitance and energy density,low cost and easy preparation.However,in conventional supercapacitors and batteries,the cathode usually consists of a mixture of active materials,polymeric binder,conductive additive and current collectors.The physical mixture of active materials and conductive additive lead to inefficient ions and electrons diffusion,which will affect the electrochemical performance.Nanoarrays,as a kind of ordered nanostructure,have been a promising candidate for electrode materials.The performance is highly dependent on the structures,so the structure and morphology of the active materials should be further explored and optimized.For the above problems,this essay will discuss the following:1?We designed and synthesized NiV-LDH nanoarrays by one-step hydrothermal method.The relationship between electrochemical performance and varying molar ratios of nickel ions and vanadium ions is also investigated.The structure of NiV-LDH nanoarrays was characterized,and the electrochemical properties of NiV-LDH nanoarrays were also studied by cyclic voltammetry,galvanostatic charge discharge and electrochemical impedance spectroscopy(EIS).NiV-LDH nanoarrays exhibit high specific capacitance(2420 F g-1 at 1 A g-1),good rate capability(44.5%can be maintained at 20 A g-1)and excellent cycling stability(68%retention after 2000 cycles),this is of great significance for practical applications.The test results showed that layered double hydroxides(LDH)structure was formed by doping 3+ vanadium ions,and NiV-LDH nanoarrays exhibit very high specific capacitance,good rate characteristics and excellent cycling stability.Because of the special structural advantages,NiV-LDH nanoarrays have the characteristics of stabilizing the crystalline phase of ?-Ni(OH)2,and achieve excellent electrochemical energy storage properties.NiV-LDH nanoarrays are reported for the first time in the world for the research of supercapacitors energy storage electrodes.Construction of nanoarrays is a promising way to build high performance electrochemical electrodes.2.We designed and synthesized a hierarchical Co3O4@NiV-LDH core-sheet arrays electrode with ultrahigh mass loading of the active materials to further enhance the areal capacity through a two-step hydrothermal reaction and a following calcination process.The structure of Co3O4@NiV-LDH was characterized and the electrochemical properties were studied.Such novel hierarchical architectures integrate the merits of macroporous nickel foam and the core/shell nanowire arrays such as remarkable electrical conductivity,large specific surface area,and shorten the ions and electrons diffusion pathway.This as-obtained Co3O4@NiV-LDH nanowire arrays with high mass-loading(?11.1mg cm-2)exhibited high areal capacity(1.98 mAh cm-2 at 5 mA cm-2),remarkable rate capability(55.6%of capacity retention at 50 mA cm-2)and excellent cycling stability(100%retention after 1000 cycles).The results show that hierarchical Co3O4@NiV-LDH core-sheet nanoarrays is suitable for the positive electrode of electrochemical energy storage materials.Therefore,the as-obtained Co3O4@NiV-LDH nanowire arrays were also used as a cathode electrode to fabricate Ni-Zn batteries,which delivered high operating voltage(1.71 V),energy density(up to 2.2 mWh cm-2),power properties(up to 82.0 mW cm-2)and remarkable cycling stability(89%retention after 1500 cycles).The improvement in electrochemical performance is attributed to the unique hierarchical structure and the component synergistic effect.This work may bring new design opportunities of well-defined nanoarrays for energy storage devices.