Morphology Control Of Transition Metal Oxide Micro-nano Structure And The Properties Of Lithium Storage

Recently,transition metal compounds nanostructures have attracted considerable attentions in new energy,owing to their integration of the size effect of nanometer materials and the structural stability of micrometer materials.And how to use simple and effective synthesis method to control the electrochemical active sites,improve ion/electron transport efficiency,reduce the powder of the electrode,and is the key to obtain advanced electrode materials.In this paper,transition metal titanium,iron and copper oxide were used as the research object,and the research method of the design,construction and forming mechanism of the new micro-nano structure with functional customization was developed.The influence of micro-nanometer and its composite structure on the electrochemical energy storage of the material was explored.The main conclusions are sumerized as follows:?1?The hierarchical Cu nanosheets @ CuO nanorods nanostructures were fabricated by a facile hydrothermal approach using Cu nanosheets as self-template and nano-substrate in an aqueous solution of NaOH/H2O2.The hierarchical Cu nanosheets @ CuO nanorods electrodes show a high reversible capacity of 620 mAh/g after 200 cycles,much higher than that of the pure CuO nanocrystals at a current 0.1C.The excellent electrochemical performance of the hierarchical Cu nanosheets @ CuO nanorods electrode can be attributed to the unique architecture,which not only provides appropriate spaces between nanorod arrays to accommodate the volume change during the discharge/charge process,but also enables fast charge transport owing to the reduced diffusion paths for electrons and induced the Cu nanosheet as the nano-substrates.?2?Hollow porous Fe₂O₃ hexagonal nanorods are fabricated by a facile and controllable approach using the MOFs as both the precursor and sacrificial template strategy.It is found that Fe?OH?3,which is formed on the surface of MOFs after treatment with NaOH solution,plays an significant role in maintaining its morphology during calcination.The interior of well-defined hollow porous Fe₂O₃ hexagonal nanorods structure are assembled by interconnected nanoparticles to form a porous network structure.Due to the excellent Li+ storage and ion transport,hollow porous Fe₂O₃ hexagonal nanorod is found to be a promising anode material for lithium ion batteries.It exhibit long-term cycling stability?1219 mAh/g after 100 cycles?and ultrahigh rate capability.The strategy provides a general route to synthesize various hollow porous metal oxides using MOF as template,which are expected to be applied in more fields.?3?A hollow porous TiO₂ nanometer cube was prepared by pretreatment with NaOH solution and Ti-MIL-125?MOFs?as precursors.Hollow porous TiO2 nanometer cube material has a large specific surface area and mesoporous structure,and its internal pore structure is composed of a large number of nanoparticles with a diameter of about 13nm.Electrochemical studies have also revealed that this unique porous structure imparts excellent cycling and magnification properties to the material.The reversible specific capacity remains at 256 mAh/g after 180 cycles of charge and discharge at 0.5C current density.The charge and discharge cycles can maintain a high capacity of 120 mAh/g and 90 mAh/g at 10C and 15C high current.The internal channels can be flooded with electrolyte,providing good accesses of the electrolyte to the electrode surface and creating a shorter distance to improved lithium-ion diffusion.Meanwhile,the hollow interior and the voids between nanoparticles provide extra free space for alleviating the structural strain and accommodating the large volume variation associated with repeated Li+ ions insertion/extraction processes,resulting in high structural stability of this electrode material.?4?The peony-like CuO micro/nanostructures were fabricated by a facile hydrothermal approach.The peony-like CuO micro/nanostructures about 3 ?m to 5 ?m in diameter were assembled by CuO nanoplates.These CuO nanoplates,as the building block,were self-assembled into multilayer structures under the action of ethidene diamine,and then grew into uniform peony-like CuO architecture.The peony-like CuO micro/nanostructures electrodes show a high reversible capacity of 456 mAh/g after 200 cycles,much higher than that of the commercial CuO nanocrystals at a current 0.1C.The excellent electrochemical performance of peony-like CuO micro/nanostructures might be ascribed to the unique assembly structure,which not only provide large electrode/electrolyte contact area to accelerate the lithiation reaction,but also the interval between the multilayer structures of CuO nanoplates electrode could provide enough interior space to accommodate the volume change during Li+ insertion and de-insertion process.