Construction Of High-performance Aqueous Zinc Ion Hybrid Capacitors Based On Porous Carbon And Manganese Oxide Materials Derived From MOFs

With the increasingly serious energy crisis,the research and development of high-efficiency energy storage devices has received extensive attention.Traditional energy storage devices such as secondary rechargeable batteries have low power density and poor cycle stability,and supercapacitors have low energy density.Their respective defects limit their practical application in large-scale energy storage devices.Water-based zinc ion hybrid capacitors(ZIHCs)have the advantages of both secondary rechargeable batteries and supercapacitors,and can provide high energy density and high power output at the same time.They are safe energy storage systems with great development potential and have attracted much attention in recent years.But there are still many problems in the system.Based on its energy storage mechanism,it is particularly important to develop capacitive electrode materials with high specific surface area,rich levels of nanoporous structure and good wettability,as well as battery-type materials with easy insertion/extraction of zinc ions.In this thesis,metal-organic frameworks(MOFs)are used as precursors,combined with material pyrolysis and chemical activation to prepare nanoporous carbon capacitive materials with different structures and MnO/C battery-type composite materials,and build a series of high-performance zinc ions hybrid capacitor.The main research contents and results of this thesis are as follows:(1)Using MIL-100(Mn)as the carbon source,the influence of pyrolysis and the amount of activator on the microscopic morphology,pore structure,specific surface area,element composition and capacitance performance of the three-dimensional porous carbon microspheres of MIL-100(Mn)derivatives was systematically investigated,Determine the best activation ratio,and screen out the three-dimensional porous carbon ball(PCMs-800-1)with the best capacitance performance.With PCMs-800-1 as the capacitive positive electrode and metal Zn foil as the battery negative electrode,the water-based zinc ion hybrid capacitors are assembled in different electrolytes,and the best electrolyte is preferred.The results show that Zn//Zn(CF₃SO₃)₂//PCMs-800-1 has the best electrochemical performance,and can achieve a high specific capacity of 379.2 F g^-1 at a current density of 0.5 A g^-1,and a high specific capacity of 379.2 F g^-1 at a current density of 20 A g^-1,it still maintains a specific capacitance of 186.4 F g^-1,showing good rate performance.At a current density of 10 A g^-1,the capacity retention rate is as high as 87.2%after 19 000cycles.At the same time,the device can also provide an energy density of up to 170.6W h kg^-1 and a power density of 18 k W kg^-1.Its excellent energy storage characteristics are mainly due to the larger specific surface area and porosity of the PCMs-800-1 material,which can provide more active sites and effectively shorten the ion transmission path,showing that ZIHCs are the next generation of new energy storage devices potential.(2)MIL-100(Mn)as the research object,MIL-100(Mn)precursors with different morphologies were prepared at room temperature and by hydrothermal method.Two kinds of MnO/C composites with different specific surface area,pore structure and morphological characteristics were prepared by high temperature pyrolysis in argon atmosphere,and their zinc storage performance was tested.The test results show that the MnO/C-P electrode material with irregular polyhedral morphology with smaller particle size,higher specific surface area and rich pore structure has better electrochemical performance(at a current density of 0.1 A g^-1,the battery has a specific capacity of 367.5 m A h g^-1)and long-cycle stability(at a current density of 3 A g^-1,the capacity retention rate is 65%after 1 000 cycles).Using it as battery electrode material,and MIL-100(Mn)derived nanoporous carbon(PCMs-800-1)as capacitive material,construct another type of zinc ion hybrid capacitor in 2 M Zn(CF₃SO₃)₂ electrolyte(PCMs-800-1//Zn(CF₃SO₃)₂//MnO/C-P),the device has a specific capacitance of 75.25 F g^-1at 0.5 A g^-1,and a high current density of 10 A g^-1.Cycling 5 000 times,the capacity retention rate is as high as 76%.At the same time,the device can also provide an energy density of up to 26.4 W h kg^-1and a power density of 25.6 k W kg^-1.This work provides a new idea for the design of next-generation ZIHCs with excellent performance,high safety,and pollution-free.(3)K-based MOFs are selected as the precursors,and the high-temperature self-activation characteristics of the precursors are used to prepare rod-shaped nanoporous carbon(RPC)electrode materials in a simple,fast and controllable manner.A water-based zinc ion hybrid capacitor is assembled with RPC material as the capacitive positive electrode,metal Zn foil as the battery negative electrode and 2M Zn(CF₃SO₃)₂ electrolyte.The results show that Zn//Zn(CF₃SO₃)₂//RPC has excellent electrochemical performance,and can achieve a high specific capacity of321.9 F g^-1 and an energy of 145.9 W h kg^-1 at a current density of 0.5 A g^-1 density.When the current density is increased to 20 A g^-1,the specific capacitance is 143.3 F g^-1,and the power density is as high as 18 k W kg^-1,showing good rate characteristics.At the same time,the capacity retention rate is as high as 95.4%under the current density of 10 A g^-1 for 15 000 cycles,showing excellent cycle stability.