Preparation And Supercapacitive Properties Of Multi-metal Oxide Nanomaterials

With the increasing awareness of environmental protection,the development of clean energy has received more and more attention,and among them,energy storage devices are particularly important.Supercapacitors are a class of energy storage devices that have stood out in recent years and are very popular.And its core lies in the electrode material.As one of the most important electrode materials,spinel-type metal oxides have attracted the attention of researchers because of their low cost,easy to get materials,high green cleaning and safety.In addition,as electrode materials,they also have the inherent advantages such as high conductivity and high chemical activity.However,such materials have problems such as low cycle life,low magnification and low energy density.In order to solve these problems,this research work improves the supercapacitor performance of spinel-type multi-metal oxide materials by adjusting the composition,adjusting the morphology,designing special structures,and constructing composite materials.The specific research contents are as follows:(1)Through simple hydrothermal technology and heat treatment method,Ni_1-xMn_xCo₂O₄nano flowers with different Ni/Mn atomic ratios were prepared.The results show that the electrochemical properties of the multi-component Ni_1-xMn_xCo₂O₄ samples are improved to some extent compared with the original Mn Co₂O₄ and Ni Co₂O₄ samples.Especially when Ni/Mn is 5:5(Ni_0.5Mn_0.5Co₂O₄),it shows the best electrochemical performance.It shows a specific capacitance of 366 F/g(154 C/g)at 1 A/g,after 3 000 cycles at 5 A/g,the capacity retention rate is 83.7%.The excellent electrochemical performance of Ni_0.5Mn_0.5Co₂O₄ can be attributed to the large surface area and high mesoporosity,as well as the enhanced electrochemical reaction under the synergistic effect of mixed metal components.The Ni_0.5Mn_0.5Co₂O₄//AC asymmetric supercapacitor prepared with Ni_0.5Mn_0.5Co₂O₄ as electrode material also has good performance.The specific capacitance at 1 A/g is 74 F/g,82%of the initial capacitance is retained after 5 000 cycles at 3 A/g,and up to 20.2 Wh/kg of energy is obtained at a power density of 700 W/kg density.This study shows that constructing a multi-element transition metal oxide with a three-dimensional hierarchical porous structure is an effective strategy to improve the electrochemical performance of metal oxides.(2)Using a two-step hydrothermal technique and a two-step heat treatment method,a sea urchin-shaped Co₃O₄@Ni_0.5Mn_0.5Co₂O₄ core/shell heterojunction(NWFs)electrode material assembled from Co₃O₄ nanowires and Ni_0.5Mn_0.5Co₂O₄ nanoflowers was prepared on foam nickel.Compared with pure Ni_0.5Mn_0.5Co₂O₄ nano flowers(NFs)and Co₃O₄ nano wires(NWs),the prepared core/shell heterojunction NFWs have a high specific capacitance(931.4 F/g or465.7 C/g at 1 A/g),high magnification(77%at 20 A/g at 1 A/g)and excellent long-cycle stability(5 000 cycles at 5 A/g maintain 91.2%of the initial specific capacitance).This excellent electrochemical performance can be attributed to the good connection between the electrode material and the current collector,as well as the unique 3D layered core/shell heterojunction synergy,resulting in rapid transmission of ions or electrons and more reactive sites point.In order to increase the energy density,Co₃O₄@Ni_0.5Mn_0.5Co₂O₄core/shell heterojunction NWFs were used as the positive electrode and activated carbon(AC)as the negative electrode,respectively,to prepare the Co₃O₄@Ni_0.5Mn_0.5Co₂O₄//AC asymmetric supercapacitor.The fabricated device exhibited a high operating window of 1.5 V,and had the highest specific capacitance of 160 F/g and a long cycle stability of 88.2%after 5 000 cycles.In addition,the device has an energy density of 50 Wh/kg at a power density of 750 W/kg.When the power density increases to 7980 W/kg,it still has an energy density of up to 26.6 Wh/kg.The preparation strategy of this study can be extended to the synthesis of other electrode materials,which is of great significance for the design of high-performance supercapacitors.