Structure Regulation Of Transition Metal Oxides And Its Application In Energy Storage Devices

The rapid economic development and the increasing consumption of fossil fuels have brought about environmental problems that pose serious risks to human health and ecological security.In order to escape from the over-dependence on fossil fuels and to improve the ecological environment,researchers are focusing on the development of renewable and clean energy sources such as wind and solar energy.However,the inherent instability of renewable energy（e.g.solar energy）requires the development of new and efficient energy storage devices to store these energy sources.Ion batteries and supercapacitors are currently commonly used energy storage devices and their electrochemical performance is mainly determined by the nature of the electrode materials used.Transition metal oxides have received much attention because their theoretical capacity is greater than that of conventional carbon electrode materials,however,their application is limited by their drawbacks such as poor electrical conductivity and cycling stability.By compounding nanosized transition metal oxides with a three-dimensional porous network with high electrical conductivity,the volume change of the electrode material during cycling can be effectively mitigated and its service life extended.In this paper,four high-performance electrode materials were prepared by combining four different transition metal oxides with high conductivity current collectors using electrochemical deposition and annealing methods,and two of them were assembled into high-performance asymmetric supercapacitors.A series of methods about microstructure characterization were used to evaluate the microstructure and apparent morphology of the electrode materials,and electrochemical characterization methods were used to evaluate the electrochemical performance of the electrode material.The main studies are as follows:（1）Vertical-aligned Ni/Ni O core-shell nanotube arrays with high performance for pseudocapacitance and lithium ion storage3D Ni/Ni O core-shell nanotube arrays are seamlessly and vertically aligned on Ni foil substrate as a binder-free electrode for supercapacitor and lithium ion battery applications.Benefiting from the structural merits and enhanced electronic/ionic conductivity,the assembled supercapacitor reveals high specific capacitance of～1426F g^-1and retains～97.6%of the initial capacitance after 20000 cycles at 71.4 A g^-1as well as excellent rate capability.Similarly,the hybrid electrode,as anode of lithium ion battery,displays excellent rate capability(reaching～1106 m Ah g^-1at 0.1 C and maintaining 412 m Ah g^-1at 4 C)and outstanding cycling performance（～93.3%retention of the initial capacity after a long-term 1000 cycle）.The facile and cost-efficient strategy can be applied to large-scale manufacture and extended to other metallic materials.（2）High-performance aqueous potassium ion asymmetric supercapacitors based on tunable 2D transition metal oxidesamorphous/crystalline biphasic K_xV₂O₅（ac-K_xV₂O₅）is synthesised by electrochemical deposition on three-dimensional nanoporous nickel tube collectors.The amorphous K_0.25V₂O₅·n H₂O acts as a molecular column to maintain the large interlayer spacing of crystalline V₂O₅bilayer,providing sufficient space to accommodate as much hydrated potassium ions as possible and their rapid transport,effectively alleviating structural damage to the host material.Benefiting from the large work function difference between V₂O₅and Mn O₂,an aqueous potassium ion asymmetric supercapacitor is assembled using K_xV₂O₅·n H₂O anode and K_xMn O₂·n H₂O cathode to obtain a volumetric energy of 32.7 m Wh cm^-3,which is superior not only to commercial energy storage devices but also to previously reported aqueous alkaline ion batteries and supercapacitors.（3）Catkin-derived hybrid anode for high-performance lithium ion batteriesAs a common biological waste,catkin shows negligible economic value and is hazardous to the environment and human respiratory health.To turn waste into treasure,in this work,a hybrid anode is successfully prepared by combining Mn O with the catkin-derived 1D hollow carbon microtube via a simple one-step pyrolysis method.Benefiting from the high electrical conductivity and hollow microtubule structure of the catkin-derived carbon,the lithium ion battery based on the resultant Mn O/C hybrid anode exhibits outstanding rate performance(high reversible specific capacity of 1365 m Ah g^-1at 0.1 A g^-1and maintains 451 m Ah g^-1even at 6.4 A g^-1)and superior cycling stability(retains～100%after 1000 cycles at a current density of 0.8 A g^-1).This work conforms to the development concept of green environmental protection and realizes the unity of economic and social benefits.