Design And Preparation Of Transition Metal Oxide Anode Materials For Lithium Storage Application

Lithium ion batteries play an important role in the field of energy,storage and application due to the superiorities of long service life,high working voltage,high energy density,non-memory effect and environmental benignity.However,as currently commercial lithium ion battery anode materials,graphite with low capacity have no longer satisfied the demand of electronic products with high energy density.With the development of portable electronic devices and electric vehicles,it is highly essential to develop new lithium ion batteries with strong endurance,good safety,high energy and power density.Compared to other materials,the transition metal oxides are one of the most promising anode materials for lithium ion batteries due to their natural abundance,low toxicity,high theoretical capacity and rate capability.Recently,researchers used various strategies to enhance the cycle stability and rate capacity of transition metal oxide anode materials,but there still remain some problems to be solved for commercialization.Therefore,in this work,we developed transition metal oxide materials with diversified micro-nano structures and explored their performance and mechanism of lithium storage,which provides an important reference value for their commercial application of lithium ion batteries.The main works and innovations are listed as follows:?1?CuFeO2@rGO and Cu/CuFe2O4@rGO composites has been successfully fabricated by a simple hydrothermal reaction.The growth mechanism,structure,morphology,components and electrochemical properties of two compounds have been investigated in detail.The results indicate that graphene can provide abundant active sites and confine the crystal size,thus to enhance the electrochemical performance.The CuFeO₂@rGO electrode exhibits a reversible capacity of 587 mAh g^-1 at 200 mA g^-11 after 100 cycles.In addition,modified Cu/CuFe₂O₄@rGO composite with multidimension structure were prepared by the introduction of reducing agent,in which ultrafine nanoparticles were evenly anchored on the graphene nanosheets.When used as anode material of lithium ion battery,the Cu/CuFe₂O₄@rGO electrode shows a high capacity of 1102mAh g^-1 at 800 mA g^-11 after 250 cycles and excellent rate performance of 841,707,647 and 560 mAh g^-1 at 100,800,1600 and 3200 mA g^-1,respectively.?2?Novel quaternary MnO-Cu-CNT/graphene composite has been successfully fabricated by a simple one-step hydrothermal reaction.The effects of Cu and carbon nanotubes on the structure,morphology and electrochemical performance have been investigated in detail.SEM and TEM images reveal that Cu could effectively relieve the aggregation of MnO nanoparticles and the introduction of carbon nanotubes along with graphene can achieve multidimensional interconnection structure,thus the MnO-Cu-CNT/graphene?MnO-Cu-CG?composite has a large specific surface area of 59.9 m² g^-1.The results of electrochemical tests indicate that the presence of carbon nanotubes and Cu can improve the charge transfer ability and surface-controlled pseudocapacitance lithium storage contribution.The MnO-Cu-CG electrode exhibits outstanding rate capacity of776,626,564,471 and 410 mAh g^-1 at 100,1000,2000,5000 and 8000 mA g^-1respectively and long lifetimes of 3500 cycles at 5000 mA g^-1 with a capacity of 558mAh g^-1.?3?Three-dimensional interconnected MnO@GS/CNT composite has been successfully prepared by a modified hydrothermal method.The relationship of the structure and cyclic stability as well as the electrochemical performance in full cell of MnO@GS/CNT have been investigated in detail.Morphology analysis indicates that MnO@GS/CNT composite is consists of MnO nanoparticles uniform distributed on the three-dimensional interconnected conductive framework based on graphene sheets and carbon nanotubes.The high specific surface area and microscopic voids can boost the charge transfer and bring more active sites for electrochemical reactions,enhancing the pseudocapacitance effect.The three-dimensional structure can guarantee the stability of active materials in cycling process.Thus,the MnO@GS/CNT electrode shows an infusive lithium storage performance of 677,580,422 and 306 mAh g^-1 at 100,1000,5000 and 10000mA g^-1,respectively.Moreover,the capacity increased gradually under low current density,but the MnO@GS/CNT electrode exhibits a stable capacity of 405 mAh g^-1 at5000 mA g^-1 after 3200 cycles.When coupled with LiMn₂O₄ cathode,the manganese based full cell characterizes an excellent rate capability and cycling stability of over100 cycles at 100 mA g^-1 with a high capacity retention of 90%.?4?Three-dimensional porous MnO based anode material?3DCG/MnO?has been successfully prepared by modified hydrothermal and solvothermal method.The electrochemical performance and mechanics of the composite have been investigated in detail.The research results indicate that MnO uniformly anchored three-dimensional porous networks?3DCG/MnO?can be successfully synthesized based on simple one-step hydrothermal method and subsequenr solvothermal method.3DCG/MnO has excellent electrical conductivity and high specific surface area of 128 m² g^-1,which is advantageous for electron transfer and ion diffusion.The homogeneous distributed MnO nanoparticles could guarantee the stability formation of SEI film,enhancing the structure stability of electrode materials.Galvanostatic charge and discharge tests show that 3DCG/MnO electrode behaves excellent rate capacity and ultra-stable cycle performance of 784 mAh g^-1 at 100 mA g^-1 after 100 cycles.When cycling at 2000mA g^-1,it performs a high capacity of 526.7 mAh g^-11 with 98%capacity retention over1400 cycles.The results of cyclic voltammetry and electrochemical impedance spectroscopy further evidence that the three-dimensional porous framework constructed by graphene and carbon nanotubes can significantly improve the conductibity,reaction activity and structure stability of composite electrode.