Fabrication Of Lithium-ion Battery Based On Transition Metal Compounds Micro/Nanomaterials

The low theoretical capacity and poor rate performance of commercial graphite anode materials have hindered the further application of Lithium ion batteries.Fortunately,owing to their advantages of high energy density,environmental friendliness and low cost,transition metal compounds are considered to be ideal anode materials for next-generation Lithium ion batteries.However,the large volume change and poor conductivity of transition metal compounds during the charge and discharge process have limited their commercial development and application.By rationally designing and constructing composite materials with special structures and morphologies,their electrochemical performance can be effectively improved.In this thesis,Mn₃O₄/CNFs composites,CNFs@MnO₂ composites,Co_xMn_?3-x?O₄/CNFs composites,and Cu/CuO self-supporting electrode are designed and constructed,and their structures,morphologies and electrochemical properties are studied in depth.The details are as follows:1.Porous Mn₃O₄/CNFs composite material is synthesized via electrospinning technology in combination with in-situ growth process followed by multi-step heat treatment.When it is used as anode material of lithium ion batteries,the reversible capacity of Mn₃O₄/CNFs-2 electrode is 754 m Ah g^-1 after 400 cycles at a current density of 0.1 A g^-1.Its excellent electrochemical performance can be attributed to the facts that the uniform distribution of Mn₃O₄ on CNFs can effectively prevent particle aggregation,the porous structure can shorten Li+ diffusion path,and the one-dimensional conductive carbon matrix can improve the conductivity of the electrode and accelerate electron transportation.2.CNFs are prepared by electrospinning technology,and then a thin layer of MnO₂ is loaded on CNFs by two methods: immersion at room temperature and hydrothermal method.As anode material for lithium ion batteries,the reversible capacity of CNFs@MnO₂-1 electrode is 1103 m Ah g^-1 after 400 cycles at a current density of 0.1 A g^-1.The CNFs cores constitute three-dimensional conductive frames to facilitate electron transportation,while the MnO₂ shell layers can improve lithium storage capacity.3.Co_xMn_?3-x?O₄/CNFs composite material is constructed by directly-electrospinning Co Mn-MOF and followed by calcination process.When it is used as anode material of lithium ion batteries,the reversible capacity of Co_xMn_?3-x?O₄/CNFs electrode is maintained at 755 m Ah g^-1 after 400 cycles at a current density of 0.2 A g^-1.Its good electrochemical performance is owing to the synergistic effect of the two transition metal oxides and the presence of one-dimensional conductive carbon nanofibers matrix.4.CuO nanosheets are successfully grown on Cu foil substrates by wet chemical oxidation strategy.When it is used as the anode of lithium ion batteries,the reversible capacity of Cu/CuO self-supporting electrode is 756 m Ah g^-1 after 450 cycles at a current density of 0.1 A g^-1.Its excellent battery performance is mainly due to the combination of the unique nanosheet morphology and the inherent advantages of self-supporting electrode.The nanosheet layer structure can increase the specific surface area of the electrode,which is conducive to lithium ion diffusion.The interlayer space can provide sufficient space for the volume expansion of CuO during the process of lithium ion insertion and extraction.