Construction And Electrochemical Performance Of Cu-based Carbon Nanofibers

With the continuous exploitation and consumption of nonrenewable fossil fuel resources,it is an urgent scientific and technological challenge to explore the alternative energy materials with the advantages of reusable and environmental harmlessness.A series of renewable energy sources have caused scientists’attention due to the clean and inexhaustible characteristics,such as solar energy,wind energy,tidal energy,etc.However,some uncontrollable factors like time random and geographic restriction greatly limit their commercial application.Therefore,it is urgent to develop high-efficiency facilities that convert and store inconstant energy where needed.Meanwhile,with the development of the century of information,there is an imperious demand for portable electronic devices.Lithium ion batteries with long cycle life,high theoretical capacity,no memory effect,and environmental harmlessness are regarded as the most promising power storage devices.Currently,the commercial carbon anodes display low energy storage capability,restricting the further enhancement of the lithium ion batteries.With improvements of the energy density of carbon anode materials,the application in the large-scale energy facilities and high-end equipment can be realized.This dissertation will investigate the Li-ion batteries including the science of material chemistry,inorganic chemistry and electrochemistry.In view of the bottleneck problem for the development of anode materials for lithium ion batteries,we investigate the synthesis mechanism,composition adjustment and electrochemical performance of copper-based carbon nanofiber composites by means of electrospinning technology.Due to the insufficient capacity of the carbon nanofibers,we adopt the transition metal oxides to ultra-uniform dispersed in carbon skeleton to improve its electrochemical performance.Based on these purposes,the followings aspects are discussed as follows:（1）Osiers-sprout-like carbon nanofibers were synthesized by a simple electrospinning and unique thermal reduction process without the process of chemical activation and template sacrifice.The added of Cu（CH₃COO）₂ in this system has two roles to obtain this special nanostructure.On one hand,the evaporation of partial external Cu led to the formation of nanosized carbon bubbles on the surface of the nanofibers.On the other hand,the inactive copper inside the nanofibers enhanced the electrical conductivity of the materials.Consequently,the resulting unique carbon nanofibers revealed storage capacities of 480 and 160 mA h g^-1 after the 900^th cycle at a current density of 800 mA g^-1 for the LIBs and SIBs,respectively.（2）Ultra-uniformly distributed CuO/Cu in carbon nanofibers was prepared by an air pre-treatment process.Compared with the pure carbon nanofibers,the introduced CuO/Cu inside carbon nanofibers showed a significant boost in the electrochemical performances,including a high specific capacity(572.0 mA h g^-1 at 500 mA g^-1),excellent rate capability,and super-long-term cycling stability（99%after 500 cycles）.（3）Utilizing the peculiarity of ZnO to reduction-evaporation during the carbothermic reduction process,the Cu₂O/Cu structure embedded in carbon nanofibers was developed.The dosage of zinc salt and copper salt had a crucial effect on the development of this unique carbon structure.A systematic analysis was performed to elucidate the possible mechanism of synthesis of the carbon nanofibers blocked structure.Furthermore,the size of particle in the nanofiber could be adjusted by the concentration of copper salt.The unique electrochemical performance of CuO_x-ZnO carbon nanofibers electrode was attributed to the limitation of Cu₂O/Cu in carbon matrix with residual ZnO.（4）Based on the advantage of high theoretical capacity of ternary transition metal oxide,ultra-uniformly distributed CuCo₂O₄/carbon nanofibers has been prepared.Compared with the CuO/Cu/carbon nanofibers in the fourth chapter of the dissertation,the electrochemical performances of CuCo₂O₄/carbon nanofibers showed a significant enhancement.In addation,the battery performance of CuCo₂O₄/carbon nanofibers could compete with recently reported CuCo₂O₄-based materials.The composite electrode exhibited a high discharge capacity of 865 mA h g^-1 at the current density of 200 mA g^-1 after 400 cycles.Furthermore,the specific capacitance still retained 785 mA h g^-1 at the current density of 400 mA g^-1 after 500 cycles(610mA h g^-1 at 600 mA g^-1 after 800 cycles).