| With rapid growth of national economy, the energy crisis, environmental problems and economic crisis gradually expose. To avoid the ignorance of resource and environmental problems caused by over-rapid economic development, it is urgent to develop sustainable, environmental-friendly and high-efficient energy storage system. Compared with lead-acid cell, nickel-cadmium cell and other secondary cells, lithium ion batteries (LIBs) and supercapacitors are widely applied in cell phones, notebooks, smart power grid, new energy automobile, etc. Particularly, they play important roles in high power devices and energy storage fields. Hence, the development of electrodes with high capacity, high stability and good safety depends on controllable material structures. The core of controllable structures is to improve the materials openness, conductivity and stability.Among so many electrodes, transition metal materials with special electrochemical mechanism have great development potential due to high specific capacity, no toxicity and low cost. However, the traditional preparation of transition metal materials is mainly based on a hydrothermal, template, chemical sputtering deposition, solid-phase synthesis, etc. These methods are more or less associated with organic solvents, templates and complex instruments. So that it is difficult to meet the requirements of openness, high stability, high capacity and mass production. Therefore, it is extremely urgent to develop a brand-new and environmental-friendly method with easy regulation, functionalization and openness. Dealloying method, an ancient and effective technology, has unique advantages of flexible preparation and wide application. It can obtain different nano-structures by regulating alloy components and corrosion conditions, meeting requirements of preparing open structure electrodes in shape and size. And there is no organic solvent in the preparation process. Combining with electrochemical method and chemical vapor deposition (CVD), we can prepare high surface cleanliness materials and establish the bridge between the electrodes structure and electrochemical reaction mechanism. Thus, the effective method of preparing the electrodes with excellent performance should be involved:carrying out functionalized modification in the dealloying process and subsequently functionalized guiding by CVD method.However, the electrodes will be subjected to agglomeration, pulverization, polarization, small electrolyte contact area and poor conductivity in preparation process. Therefore, we have conducted the design research of transition metal materials with micro/nano structure for supercapacitor based on modified dealloying technology. Through the subsequent CVD, we have prepared porous transition metal oxide microspheres as anode for lithium ion batteries. Because of poor conductivity of electrodes, the transition metal oxide is doped and/or coated with carbon materials to further improve conductivity, specific capacity and stability. Besides, we design a series of controllable experiments to regulate the metal oxide growth to avoid the change of morphology, size and phase in high-temperature annealing. So, we emphasize on developing preparation of transition metal electrodes based on the dealloying technology. And different transition metal oxide electrodes are prepared by the subsequent CVD technology for LIBs. And the richening and development of dealloying technology has guidelines on the preparation of morphology, phase and size of other nanomaterials. The main researches of the paper are as below..1. Controlled synthesis of hierarchical Na0.55Mn2O4 nano-flowers for supercapacitorsMn5Al95 alloy in 5:95 atomic ratio are prepared by melt-spinning technology, and hierarchical Na0.55Mn2O4 nano-flowers are synthesized by dealloying technology with hydrogen peroxide. The formation mechanism is proposed by different reaction time. The functionality of H2O2 is suggested to be weak oxidant to gain more seeds for hierarchical nano-flowers by the electrolyte-species-solid mechanism using XRD pattern and TEM techniques. And it can improve the interfacial interaction between electrolyte and alloys and control the growth of the crystal surface and the size of sample. After 2000 discharge/charge cycles at 2 A g-1, the Na0.55MnaO4 nano-flowers electrode can exhibit a high capacitance of 284 F g-1 with 4.7% decrease rate than fresh electrode, indicating that the layered structure is benefit of hydrous Na+ insertion and deinsertion in the crystal lattice.2. Construction of porous MnOx micro/nano structures and their lithium anode propertiesWith the rapid development of lithium-ion batteries, it is a new challenge for construction of anode materials with high specific capacity and high stability. Porous MnOx anodes can be fabricated by dealloying Mn/Al alloys and upon annealing. The XRD pattern shows that the MnOx are composed of MnO and Mn3O4. The TOPAS crystal structure refinement of MnOx shows that relative amount of MnO is about 74.9 wt.%. When tested as anode materials for lithium ion batteries, those porous MnOx microspheres exhibit high specific capacity of 1018,901 and 757 mAh g-1 after 100 cycles at 100,200 and 500 mA g-1, respectively. The cell can recover a high reversible capacity of 771 mAh g-1 after 50 rate cycles. The enhanced storage capacity for the electrodes are ascribed to that the porous micro/nano structure can provide high surface area, short diffusion transport, high tap density, and buffer the volume change.3. Construction of porous MnO@C/CNTs micro/nano structures and their lithium anode propertiesWe firstly show that porous MnO@C/CNTs micro/nano structures are fabricated via a facile dealloying method followed by a catalytic chemical vapor deposition (CCVD) treatment. These hybrid porous structures are composed of MnO nanoparticles which are surface protected with 4 nm carbon layers and electrically enhanced by in-situ carbon nanotube spacers. The CNTs anchored to MnO@C architectures with 3D networks. As lithium ion battery anodes, these porous MnO@C/CNTs microspheres exhibit remarkable cycling performance, high specific capacity (1266 mAh g-1 after 300 cycles at 500 mA g-1), and good rate capability (850 mAh g-1 after 100 cycles). The inspiring electrochemical performance is attributed to the carbon coating layer and porous micro/nano structures for buffering the volume expansion, and carbon nanotubes for enhancing the electric conductivity of MnO anode materials.4. Construction of hierarchical MnO2 and MnO nano-flowers and their lithium anode propertiesHierarchical MnO2 and MnO nano-flowers are successfully fabricated via a facile dealloying method followed by annealing. Besides, thin nano-sheets can turn into nanorods, which inherit micro/nano structures by different conditions. As lithium ion battery anodes, hierarchical MnO nano-flowers exhibit a remarkable specific capacity of 609 mAh g-1 after 300 cycles at 2 A g-1. The cell can recover a high reversible capacity of 1369 mAh g-1 after 100 rate cycles. The inspiring electrochemical performance is attributed to hierarchical structures with high surface area, high tap density, fast lithium ion intercalation and deintercalation and buffer volume expansion. |
