Design,Synthesis And Energy Storage Applications Of Metal Oxide/Sulfide With Hollow Micro/nano Structures

With the increasing demand for energy and the depletion of fossil fuels,it is essential to develop clean energy storage systems.At present,commercial secondary lithium-ion batteries require more and more high energy density,power density,cycle life and other requirements.Coupled with limited lithium resources,the traditional lithium-ion battery system is facing great challenges.The development of new low cost and high energy storage systems has become an important task for scientific researchers.As one of the important components of batteries,electrode materials are the development core of improving the performance and reducing the cost of energy storage batteries.Hollow micro/nano structural materials with their unique structural characteristics,such as large specific surface area,high volumetric ratio,low density,high loading,have broad application prospects in the field of energy storage.The design and fabrication of multi-functional hollow micro/nano structural materials are of great significance to the development of energy storage.Therefore,this paper aims to develop a series of electrode materials with multi-stage structure and composite components,and exhibit excellent electrochemical energy storage performance.At the same time,the preparation mechanism and construction strategy of hollow micro/nano multistage composites were studied,and the efficient energy storage mechanism was explored.Based on the in-depth analysis of the structure-performance structure-activity relationship,a new type of high performance electrode material was developed.This paper consists of three parts,including the following:(1)One-step thermal annealing approach,including simultaneous carbonization and sulfidation of Ni-MOFs,is developed to synthesize hollow NiS2 spheres composed of small NiS2 nanoparticles embedded in graphene layers.The in-situ fonned graphene thin layer(1.5 nm)fully coated on the surface of NiS2 nanoparticles(20-30 nm).When the as-derived hollow NiS2@G spheres with high NiS2 content of 83%is evaluated as the anode materials for SIBs,it delivered a prominent capacity of 848 mA h g-1 after 100 cycles at 0.1 A g-1(close to the theoretical capacity of NiS2)and a remarkable rate capacity of 527.8 mA h g-1 even at 2 A g-1.(2)A hollow sphere structure was designed to encapsulate sodium titanium-based(Na2Ti3O7)ultrathin nano-sheets in three-dimensional reduced graphene oxide(rGO).Ultra-thin nano-lamellar structures,as hollow sphere blocks,provide a more suitable ion transport channel at the particle level.In addition,the porous structure produced by the hollow spheres encapsulated between the rGO layers provides a large specific surface area in contact with the electrolyte,which optimizes ion transport at the electrode level.The complete binder free NTO@rGO film exhibited excellent rate performance.At current density of 500 mA g-1 and 650 cycles,the capacity of the synthesized unbonded NTO@rGO film is as high as 135 mA h g-1.The results prove that this unique three-dimensional structure has advantages.In addition,hollow structure and reduced graphene nanosheet can alleviate pressure and volume expansion,so the prepared membrane structure has good durability.(3)A novel porous wall-like three-dimensional hollow frame structure assembled by alpha-manganese dioxide(?-MnO2)nanowires was synthesized by template-induced hydrothermal reaction and calcination as cathode catalyst for Li-O2 batteries.The prepared materials have excellent properties,including 3D continuous hollow network structure,hierarchical porous structure and high catalytic activity of ?-MnO2.These characteristics meet the requirements of electrocatalysts for Li-O2 batteries.Benefitting from these features,3D?-MnO2 achieves a high specific capacity of 8583 mA h g-1 at a current density of 100 mA g-1,a superior rate capacity of 6311 mA h g-1 at 300 mA g-1,and a good cycling stability of 170 cycles at current density of 200 mA g-1 with a fixed capacity of 1000 mA h g-1,outperforming those of recently reported MnO2-based electrocatalysts.The outstanding electrochemical performance is mainly ascribed to the 3D hierarchical hollow ?-MnO2 framework with substantially improved ORR/OER catalysis.