Studies On The Preparation Of Micro/Nano Hierarchical Conversion Anode Materials And Lithium(Sodium) Storage Performance

Exploring high energy density electrode materials for rechargeable batteries are important for the development of energy storage technologies.Electrochemical conversion reactions,which can provide high capacity through reversible multi-electron reactions with lithium?sodium?ions,are considered as one of the effective ways to develop high energy density rechargeable batteries.In this thesis,micro/nano hierarchical structures were designed to solve the problems of slow kinetics and poor cyclability for conversion materials.Amino-terminated hyperbranched polymer?AHP?was used as template to prepare micro/nano hierarchical metal oxides and sulfide conversion compounds,which were investigated as anode material for high capacity lithium?sodium?ion batteries.Further,the relationship between lithium?sodium?storage and micro/nano hierarchical structures was studied,as well as the function of flexible 3D network constructed by template in optimizing the kinetics performance and cyclic stability.This thesis would provide theoretical guidance and technical support for the development of high-capacity lithium?sodium?storage conversion materials.The main contents of this thesis are as follows:?1?Fe₂O₃ microspheres were prepared using AHP template and investigated as lithium storage materials.The morphology and microstructure of Fe₂O₃ microspheres can be significantly regulated by the AHP template.Fe2O3 single crystal microspheres with uniform and regular size distribution can be obtained when the molar ratio of AHP to Fe³⁺is 2:1.The polymer molecules are uniformLy dispersed in the Fe₂O₃microspheres,and assemble the nanosized Fe₂O₃ particles into microspheres.Compared with the heat treated Fe₂O₃-AHP-2-500 electrode,the Fe₂O₃-AHP-2electrode shows better electrochemical performance,retaining a reversible capacity of⁷70 mAh g^-1 after 700 cycles at current density of 1 A g^-1.TEM observation reveals that the polymer template dispersed in the Fe₂O₃ microspheres can stabilize the electrode structure during the cycle,alleviate the volume expansion associated with the transformation of the electrode structure,prevent the agglomeration of nanoparticles,reduce the charge transfer resistance of the electrodes,and effectively improve the kinetics performance and cycle stability of the Fe₂O₃ microsphere electrodes.?2?Cu₉S₅ microflowers were prepared using AHP template and investigated as sodium storage materials.It was observed that AHP template could significantly regulate the hierarchical structure of Cu9S5.UniformLy distributed Cu9S5 microflowers can be obtained when the ratio of AHP and Cu²⁺is 1.5:1,in which the AHP polymer is well-distributed in Cu₉S₅ nanosheets.The prepared Cu₉S₅-AHP-1.5 has excellent sodium storage performance,providing a high reversible capacity of 429 mAh g^-1 at100 mA g^-1,a remarkable coulombic efficiency of 94%at the first cycle,even 300 mAh g^-1 at high current density of 20 A g^-1 and a long-term cycle ability with a 82%capacity retention over 1000 cycles.Further kinetics studies show that AHP as an electrode additive can improve the sodium ion diffusion rate,and the flexible network can prevent the agglomeration of nanoparticles,improving the rate performance and long cycle stability of the material.?3?NiS microspheres were prepared using AHP template and investigated as sodium storage materials.NiS microspheres with different proportions of AHP and Ni²⁺were prepared.NiS microspheres with uniform size could be obtained when the ratio of AHP and Ni²⁺was 2:1.The polymer skeleton of AHP was evenly dispersed in NiS nanorods.The NiS microspheres exhibit excellent sodium storage performance,providing a high reversible capacity of 540 mAh g^-1 at 100 mA g^-1,a remarkable coulombic efficiency of 91%at the first cycle,a high capacity of 316 mAh g^-1 at 20 A g^-1,and a long-term cycleability with a 85%capacity retention over 1000 cycles.The mechanism study shows that reversible reaction occurs between NiS and metallic Ni during cycling.Further kinetics studies show NiS-AHP-2 has a high Na⁺diffusion rate,and the uniformLy dispersed polymer molecules in the material can effectively maintain the structural stability during the cycling process,thereby improving the rate performance and long-cycle performance of the electrode material.