| With the increasing demand for lithium-ion batteries,it has become a research hotspot to find anode materials for lithium-ion batteries with high capacity,excellent rate performance and stable cycle performance.Silicon-based materials are the most potential research objects due to their advantages of high specific capacity,high safety and low delithium potential（<0.5 V VS.Li/Li+）.However,in the process of charging and discharging,silicon based materials face problems such as large volume expansion and poor electrical conductivity,which seriously hinder the industrial application of silicon based materials.This paper using molecular simulation technology from the Angle of the micro molecules/atoms to simulate the electrical properties of silicon material,before and after modification model and optimize the structure of modified silica based materials,the calculation model of electron energy,the comparison and analysis the change of energy data,draw a structure model of band distribution,total density of states and state density information.Then,under the guidance of simulation results,the modified silicon-based materials with excellent performance and good cycling stability were prepared.The main research contents of this paper are as follows:1.The crystal model of Ge modified SiO was established.After structure optimization,the changes of electrical properties between the SiO model and the metal Ge before and after the introduction were calculated by molecular dynamics.The introduction of GE reduces the band gap and changes the peak value of electronic states,indicating that the modification of GE can significantly improve the conductivity of SiO.Based on the simulation results,the charge transfer resistance of the metal Ge modified SiO thin film electrode material decreased from 200 ohm to 100 ohm,and showed excellent cycle stability（the capacity remained 859.3m Ah/g after 150 cycles of 0.1C）.The introduced Ge coating alleviates the volume expansion of SiO,contributes a certain reversible capacity,and reduces the contact between SiO and electrolyte and the side reactions at the interface.2.The crystal model of N modified SiO was established.After structure optimization,the change of material properties before and after SiO model and N composite was calculated by molecular dynamics.The introduction of N reduces the band gap of the model and changes the peak value of electronic states,indicating that the introduction of N can improve the conductivity of SiO.Based on the simulation results,the ionic conductivity of the nitride modified SiO electrode material is increased from 2.5×10-4S/cm to 8.9×10-4S/cm,and the first Coulomb efficiency is increased from 38.4%to 55.1%.The retention rate of 100 cycles of the composite modified by manganese acetate coating and carbon coating increased from28.7%to 60.3%and 75.1%,respectively.3.The crystal model of lithium titanate and silicon composite（LTO-Si）was established,and its energy band and density of states were calculated by molecular dynamics after structure optimization.By contrast,it is found that Si atoms are embedded in the gap of LTO to reduce the band gap,indicating that the introduction of Si can improve the conductivity of LTO.Then,based on the simulation results,LTO powder target and Si target were used as sputtering sources to prepare LTO-Si composite films by RF magnetron co-sputtering method.The Si-doped LTO films have a high reversible capacity of nearly 800m Ah/g at100m A/g,excellent rate capacity（approximately 600m Ah/g at 1000m A/g）and excellent cycle stability（capacity maintained over 76%after 1000 cycles）.As a transition layer to conduct lithium ions and buffer the volume change of silicon material,LTO with stable structure plays a good buffer role in the periodic volume change process,forms a stable protective structure,and reduces the volume expansion of Si thin film layer.At the same time,the direct contact between Si and electrolyte is avoided to realize the rapid migration of lithium ions. |
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