Research On The Application Of Transition Metal Oxides In Aqueous Electrochemical Energy Storage Devices

The gradual depletion of traditional fossil energy sources and the environmental problems they cause have made the development of new energy technologies increasingly important,so the development of new energy storage devices has become imminent.The widespread application of lithium-ion batteries has been severely hindered by their high cost and serious safety issues.Water-based energy storage devices（such as supercapacitors and water-based zinc ion batteries）are expected to be the next generation of energy storage devices to replace lithium-ion batteries because of their environmental friendliness,excellent safety and low cost.Currently,one of the main ways to improve the energy density,power density,and cycling stability of aqueous energy storage devices is to develop high-performance electrode materials.Transition metal oxides are an excellent electrode material because of their many different valence states and structures as well as excellent redox reaction activity,which can provide uncommon capacity.However,the simple nanostructure of transition metal oxides,structural changes during the reaction,and poor electronic and ionic conductivity can lead to relatively poor cycling and multiplicative performance.In this thesis,the electrochemical properties of transition metal oxides as electrode materials for energy storage devices are systematically investigated through the design and modification of their structures.（1）Three-dimensional（3D）nano-folded transition metal oxides with well-defined structures were prepared by oxidizing the corresponding transition metals in a fast and scalable dynamic thermal oxidation scheme.Self-supported 3D nano-folded Ni@NiO electrodes were obtained using nickel foam as the base material,and their fold degree could be adjusted by changing the thermal oxidation parameters.In addition,the 3D nano-folded Ni@NiO shows excellent electrochemical performance with a specific capacitance of 0.23 F cm^-2 when operating as a supercapacitor cathode at a scan rate of 2 m V s^-1,and maintains 50%of the original specific capacitance when the scan rate is increased to 50 m V s^-1.This excellent performance is attributed to the nano-fold structure that increases the electrochemical active sites and promotes the diffusion of ions.（2）Zn²⁺was pre-embedded into the structure of MnO₂（both Zn-MnO₂）by simple in situ CV deposition.The specific capacity and cycling performance of the aqueous Zn-ion battery based on the Zn-MnO₂ cathode were significantly improved relative to the pristine MnO₂.The specific capacity reached 218 m Ah g^-1 at a current density of 0.1 A g^-1.The capacity decay of the cell per cycle was only 0.029%when cycled for 1000 cycles at a current density of 1 A g^-1.The pre-embedding of Zn²⁺not only stabilized the structure of MnO₂,but also broadened the layer spacing of MnO₂ and reduced the voltage difference between the charge and discharge curves.In addition,the discharge process of aqueous Zn-ion batteries including the co-embedding of H⁺and Zn²⁺was elucidated by galvanostatic intermittent titration technique（GITT）.This thesis lays some experimental and theoretical foundations for the application of aqueous electrochemical energy storage devices through the development of high-performance transition metal oxide electrode materials.