Construction Of Asymmetric Supercapacitors Based On Multiple Transition Metal Compounds Materials

As a new energy storage device,supercapacitors have the advantages of both traditional capacitors and batteries,and have attracted the attention of researchers worldwide.However,in practical applications,it is still very limited due to the low energy density.According to the calculation formula of the energy density of supercapacitors:E=1/2 CV²,it can be known that there are two main ways to increase energy density:one is to design and prepare a new electrode material with high specific capacity?C?,the other is to assemble an asymmetric supercapacitor to obtain a wide voltage window?V?.This thesis mainly designsed and prepareed binary metal oxides(W_0.4Mo_0.6O₃ nanoneedle),rare earth element dopeded metal oxides?Ce-doped NiMoO₄nanosheets?,binary metal oxide nanocomposites?Fe₃O₄@Bi₂O₃?,hydroxide composite materials?NiMoO₄@NiCo-LDH?and biomass carbon materials as electrode materials,and a new asymmetric supercapacitor was constructed using appropriate electrolytes to further enhance the overall performance of the device.The main research contents and results are as follows:1.A novel binary tungsten molybdenum oxide(W_0.4Mo_0.6O₃)nanoneedle array was prepared by a one-step hydrothermal method without the assistance of a surfactant.The W_0.4Mo_0.6O₃ material had a unique nanoneedle array structure and rich reactive sites to effectively promote the diffusion of electrolyte ions and shorten the electron transport path,thereby showing high electrochemical performance.In a three-electrode system,using 1 M H₂SO₄ as the electrolyte,the W_0.4Mo_0.6O₃ nanoneedle array had a high specific capacity of 115.7 mAh g^-1 at a current density of 1 A g^-1,and had good capacity rate performance.In order to achieve the high energy density of supercapacitor,an asymmetric supercapacitor was fabricated by using the W_0.4Mo_0.6O₃ nanoneedle arrays as the negative electrode and the polygni multiflori caulis-based honeycomb-like carbon?PMCHC?as the positive electrode to construct a new PMCHC//W_0.4Mo_0.6O₃asymmetry supercapacitor?ASC?.The ASC had a wide voltage window?1.5 V?and an energy density of 20.2 Wh kg^-1 at a high power density of 750.6 W kg^-1.This simple synthesis strategy and excellent electrochemical performance indicate that the binary metal oxide nanoneedle array is a promising electrochemical energy storage material.2.The Ce-doped NiMoO₄ nanosheets were synthesized by a hydrothermal method for asymmetric supercapacitors.The doping of Ce ions into the sheet structure of NiMoO₄ material improves the crystallinity,which is beneficial to the synthesis of the sheet structure and improve the electrochemical performance of the material.In a three-electrode system,using 2 M KOH as the electrolyte,the Ce-doped NiMoO₄nanosheet electrode material had a high specific capacity of 107 mAh g^-1 at a current density of 1 A g^-1.In addition,the Ce-doped NiMoO₄ nanosheet positive electrode had excellent electrochemical performance,maching the Fe₃O₄@Bi₂O₃ nanocomposite negative electrode,forming an asymmetric supercapacitor?ASC?.The ASC had a wide output voltage?1.65 V?and high energy density(32.8 Wh kg^-1 at a power density of 415W kg^-1).The research results show that Ce-doped NiMoO₄ nanosheets can be used as candidate electrode materials for supercapacitors.The asymmetric supercapacitors constructed are a practical energy storage device with high energy density and good stability.3.Two-step hydrothermal method was used to design and prepare a new type of NiMoO₄ nanorod with uniformly loaded NiCo-LDH ultra-thin nanosheets?NiMoO₄@NiCo-LDH nanocomposite?.In a three-electrode system,using 2 M KOH as the electrolyte,NiMoO₄@NiCo-LDH nanocomposites had high specific capacity(156.7mAh g^-1 at a current density of 0.5 A g^-1)and excellent cycle performance.In addition,a water-based asymmetric supercapacitor with a wide operating voltage?1.65 V?was designed and constructed using NiMoO₄@NiCo-LDH nanocomposite as a positive electrode and KOH activated horsetall tree-based carbon?AHTC?as a negative electrode.This device has a high energy density(40.3 Wh kg^-1 at a power density of425.5 W kg^-1)and excellent cycling performance?capacity retention rate reaches 85.5%after 10,000 cycles?.Therefore,the new NiMoO₄@NiCo-LDH nanocomposite designed in this paper can be used as a supercapacitor electrode,which can greatly improve the performance of materials and devices and provide an excellent strategy for the development of new energy storage devices.