| The popularity of electric vehicles,intelligent wearable devices and various electric tools puts forward higher requirements for the energy density and cycle life of lithium-ion batteries（LIB）.At present,the commercial lithium battery prepared with traditional materials has approached the energy density limit of 300 Wh/kg,so it is difficult to make a qualitative breakthrough.Silicon,the most promising candidate cathode material,has attracted much attention because of its high capacity,low production cost and environmental friendliness.However,the repeated volume expansion/contraction and continuous interface reaction seriously hinder the commercialization of silicon anode.The huge volume change leads to the structural damage of silicon particles and the continuous formation of solid electrolyte interface（SEI）,resulting in the problems of low first charge and discharge efficiency,fast capacity attenuation and fast rate performance decline of silicon materials.These problems have further led to the stagnation of the commercialization of silicon anode.Based on the above problems,this paper has carried out the following research work from the aspects of improving the coulombic efficiency and conductivity of silicon-based negative electrode and alleviating the volume effect in the process of charge and discharge of silicon materials:（1）Firstly,the structural model of silicon material is established by using Materials Studio（MS）software,and then the solid lithium source electrolyte is inserted into it.The influence of lithium source electrolyte on the structure and properties of silicon material is studied by simulating and comparing the changes of energy band and density of States after lithium source electrolyte is inserted into pure silicon model.Then,under the guidance of the simulation results,the silicon film with preset lithium source electrolyte is obtained by magnetron co-sputtering,and its properties are studied.The implanted solid lithium source electrolyte will not only participate in the formation of SEI on the surface of the silicon film,but also induce the formation of SEI inside the silicon film.At the same time,solid lithium source electrolyte can effectively absorb the stress caused by volume expansion,and improve the electrode stability of silicon film in the process of circulation.The thickness of silicon film implanted with solid lithium source electrolyte is～10μm.It has an initial coulombic efficiency higher than 92%at a current density of 400 m A/g,and can provide a specific capacity of 2135 m Ah/g and a capacity retention rate of 87%after 150 cycles.（2）The structural model of manganese dioxide is constructed by MS software,and then silicon atoms are inserted into it.The effects of different number of silicon atoms on the structure and properties of manganese dioxide matrix are studied by comparing the changes of energy band and density of states of manganese dioxide model with different number of silicon atoms.Then,under the guidance of the simulation results,silicon manganese（Si-MO）composite films were obtained by magnetron co-sputtering of manganese dioxide and silicon target,and their properties were studied.In the design of Si-MO,Mn O2 matrix provides structural support,and Si contributes capacity as the main body of energy density contribution.In the cycle performance test at 420 m A/g current density,the first reversible specific capacity of silicon manganese composite oxide film is higher than 1100 m Ah/g,and can maintain stably for 1000 cycles.（3）The structural model of silicon material is constructed by MS software,and then germanium atom and nitrogen atom are inserted into it.The effects of germanium and nitrogen on the structure and properties of silicon material are studied by comparing the changes of energy band and density of States after germanium and nitrogen are doped into pure silicon model.Under the guidance of the simulation results,the pure silicon target and pure germanium target were sputtered by magnetron sputtering in the mixed atmosphere of argon and argon nitrogen,respectively.The silicon germanium nitrogen（Si-Ge-N）composite films were obtained,and their properties were studied.When nitrogen and germanium with high lithium ion diffusion efficiency are introduced into silicon at the same time,the lithium ion transport path in the process of lithium lithiation/delithiation is shortened,and the conductivity and high rate cycle stability of silicon germanium nitrogen composite films are improved.After 200 cycles at 420 m A/g,the ternary silicon germanium nitrogen composite film can still provide a specific capacity of 1644 m Ah/g and a capacity retention rate of～90%. |
