Synthesis Of Nanocomposites With Core-shell Structure By Surface Coating Techniques And Their Electrochemical Properties

With the developement of science and technology,mobile electronic devices have rapidly entered many different areas where people work in or live in,and have made great contributions to addressing energy shortages and environmental issues.Recently,the mobile electronic devices have been developed rapidly due to the presence of lithium ion batteries.However,in face of increasing demand for energy density,it is of great importance to develop lithium ion batteries with higher capacity,longer cycle life and better cycle stability.The research and development of electrode materials,which was an important part of lithium-ion batteries,with more excellent electrochemical performance is essential,and this is an effective way to solve the problem.The electrochemical properties of the electrode highly depend on the structure and morphology of the electrode material,so the preparation of electrode materials with special structure and morphology is of great significance.Nanocomposites with core-shell structure,which are a new nano-functional materials developed in recent years,combine the advantages of core materials and shell materials,and even produce new functions which are not available in both materials.In this paper,three electrode materials were modified by surface coating method to construct core-shell structure.Different shell materials were selected for the characteristics of three core materials,and the electrochemical properties of the composites were further studied.The main research contents include the following three aspects:(1)In Chapter 2 of this paper,NCM811@ZnO core-shell nanocomposites are prepared by coating ZnO on the surface of NCM811 with atomic layer deposition system,which are used as cathode for lithium ion batteries.It is demonstrated that an appropriate thickness of ZnO shell can significantly improve the material cycle stability and rate performance.(2)In the third chapter,core-shell MnO@C nanocomposites are synthesized by annealing MnO microspheres treated with oleic acid as carbon source,which are used as anode for lithium ion batteries.It is shown that the obtained MnO@C nanocomposites exhibit excellent electrochemical performance,which is far superior to the uncoated MnO electrode.The discharge specific capacity of MnO@C electrode remains 421 mAh g'1 at 100 mA g-1 after 50 cycles,while only 143 mAh g'1 is left for the MnO electrode.(3)In chapter 4,the tube-like core-shell structured CNT@ZnO nanocomposites are synthesized by a simple liquid-phase method using CNTs as a conductive support.It demonstrates that the structural design of CNT@ZnO,which exhibits the superior cycle and rate performance as anode for lithium ion batteries,makes it obtain the dual advantages of ZnO and multi-walled carbon nanotubes.The optimized CNT@ZnO exhibits a discharge capacity of 709.2 mAh g-1 at 100 mA g-1 after 50 cycles,much superior than pure ZnO and multi-walled carbon nanotube electrodes.