Investigations Of The New Method For Preparing Lithium Ion Battery Silicon-based Anode

Silicon material can be a candidate of the lithium ion battery anode material with a great application prospect for the high specific capacity,low voltage and abundant storage.However,the great volume expansion during the lithiated process results in materials pulverization and the loss of electrical contact between active material and current collector,which leads to poor cycle performance and even failure.So the silicon-based lithium ion battery has not been large-scale commercial applications.In order to overcome the negative effects of volume expansion,the preparation of the special structure of silicon based materials and the low cost,simple and efficient method is the key.This paper puts forward that using the high pressure cold gas dynamic spray technique to prepare the silicon electrode,and study the morphology,microstructure and electrochemical properties of the pure silicon coating and Cu/Si composite coating with the experiment and simulation methods,which provides an effective solution for the new silicon-based electrode.Firstly,the silicon powder with different sizes and shapes was deposited by the high pressure cold spraying equipment independently developed by the laboratory,and the pure silicon coating was successfully prepared.The samples mass before and after spraying is measured by the analytical balance,the silicon powder deposition efficiency is different from common metal powder,and further explores the mass reduced reasons.The scanning electron microscopy,element analysis and spectrum analysis were used to analysis the coating surface morphology and cross section morphology.Further,the effects of spraying parameters,spraying pass and feeding rate and particle size on the pure silicon coating morphology are invetigated.The deposition characteristics of non-spherical silicon powders were obtained by layer spraying and single particle deposition.The silicon coating film was firstly prepared using the chemical method.The morphology and structure of the surface and interface were compared and found out the bonding mechanism of the silicon coating.The prepared pure silicon coating was assembled into a coin cell and tested its electrochemical cycling performance.The interface properties between the silicon powder and copper substrate in cold spraying are very important for the morphology,microstructure and electrical properties of silicon coatings.To this end,the first principle based on density functional theory is adopted to explore the bonding mechanism of silicon and copper.In the calculation,firstly,the Si/Cu interface model was constructed,and the interface adhesion work was calculated which suggested the fabrication location of the Si/Cu interface system.The bonding properties of the interface are analyzed through local and total state density,and it is proved that there are chemical bonding in the Si/Cu interface with covalent bonding and ionic bond characteristics.The irregular shape and high hardness of silicon powder leads to different flow characteristics from spherical metal powder.Using the fluid dynamics from the macroscopic scale to study the effect of micro-sized particle shape factor on the dynamic and deposition characteristics in the supersonic airflow,which replenish the particle deposition characteristics of existing conclusions.The variation of the particle impact parameters with the shape factor in the different carrier gas pressure and the main gas temperature and temperature are analyzed.Finally,the used cold spray nozzle was optimized based on one dimensional isentropic flow calculation and used the optimized nozzle prepared the Si/Cu composite coating.The composite coating morphology and microstructure prepared were compared and analyzed by different process parameters and copper percentage,and optimized parameters were obtained for prepared the Si/Cu composite coatings.Composite coatings with different morphology and structure were prepared by point spraying,layer spraying and gradient spraying.The deposition behavior and characteristics of composite powders were analyzed.The electrical performance of Si/Cu composite electrode with different parameters was tested and compared with pure silicon electrode.In the paper,the pure silicon and Si/Cu composite coatings were firstly successfully prepared with high pressure cold spraying technology and its electrochemical cycling performance as the anode of lithium ion battery was tested.The conclusion lays the foundation for the cold spraying method to be a kind of simple,low cost,high efficiency,large-scale commercial silicon electrode preparation method and has very important significance for engineering applications.