Preparation And Electrochemical Properties Of Silicon/Carbon Composite Thin Film Anode For Lithium Ion Battery

Energy storage is a key enabler for modern life.Li-ion batteries have now been in commercial production for 30 years.Lithium-ion batteries（LIBs）are recognized as the most important power supply for portable electronic devices and mobile phones.However,lithium-ion batteries have sometimes been outpaced by practical requirements,such as hybrid electric vehicles（HEVs）and fully electric vehicles（EVs）.One way to solve these problems is to pursue the development of new electrode materials with higher energy density,higher safety performance and longer cycle life than traditional materials.The silicon anode is considered to be a very promising next-generation LIB material due to its high theoretical specific capacity and low working potential.Yet,the huge volume change of silicon during charging and discharging leads to poor electrochemical cycling performance and unstable structure.This article aims to use graphene with excellent conductivity,high strength and toughness,and silicon thin-film electrode materials with high tap density and high theoretical specific capacity as the active material of the electrode material to realize the controllable preparation of graphene/thin-film silicon composite films.By constructing a lithium-ion battery based on graphene/thin-film silicon composite film,systematically study the electrochemical and mechanical properties of silicon thin-film electrodes,understand the relationship between film thickness and electrochemical and mechanical properties in thin-film electrode materials,finally,obtain high-performance graphene/thin-film silicon composite film lithium-ion batteries.The research content is as follows:1)Based on magnetron sputtering technology,three silicon thin films（100 nm,300nm,500 nm）are deposited on copper foil to prepare silicon thin film/copper foil negative electrodes,which are directly used as negative electrode materials to assemble half-cells.By studying its electrochemical performance,morphology characterization,and finite element analysis,the effect of thickness on the structural stability and electrochemical behavior of silicon thin film electrodes is clarified.2)Based on the silicon film/copper foil negative electrode,using acetylene as the carbon precursor,chemical vapor deposition（CVD）of carbon layers of different thicknesses on the surface at a lower temperature（650℃—700℃）,by changing the atmosphere flow,heat treatment temperature and Factors such as deposition time,control the thickness of the carbon layer,study and optimize the electrochemical performance and structural stability of the silicon thin film/copper foil anode.3)Based on the silicon thin film/copper foil anode,using methane as the precursor,depositing graphene coatings of different thicknesses on the surface through CVD and Plasma enhanced chemical vapor deposition（PECVD）techniques.By changing the precursor gas flow rate,temperature and deposition time and other factors,the influence of different graphene coverage thickness on the electrochemical performance and structural stability of the silicon film/copper foil anode was studied.And through the characterization study before and after graphene transfer,CVD graphene growth directly on the silicon film.4)Based on the silicon film/copper foil negative electrode,the graphene oxide is prepared by the improved Hummers method,the graphene oxide is covered on the surface of the silicon film,and the graphene/silicon film composite film electrode material is constructed by a chemical reduction method.On the other hand,by chemical vapor deposition technology,a graphene cover layer is deposited on the surface of the silicon film to construct a graphene/silicon film composite film electrode material.Through its electrochemical performance,microstructure characterization and finite element analysis,the positive influence of the graphene coating in the silicon film electrode is determined.And the relationship between the thickness of the graphene coating and the electrochemical performance and structural stability of the silicon thin film electrode.We demonstrate that the graphene coating helps to enhance the mechanical stability of the silicon thin film electrode and slows down the cracking and delamination tendency of the silicon thin film.The 13 nm graphene covered 100 nm silicon film retained a specific capacity of more than 2479m Ah g^-1 after 200 cycles.