Computational Study Of Polyanion-Type Cathode Materials And Al-Sm Amorphous Metal

Throughout the human history,progress in various technologies often rely on the development of materials.Traditional process of developing a material always needs a lot of manpower,material resources,and time cost.As the computational power grows,it becomes more and more convenient to simulate the motion of nucleus&electrons and predict the structure&properties of a given material.In this thesis,we preformed computational studies on two type of polyanion cathode materials of lithium-ion battery(LiFePO4 and Li2FeSiO4)and one type of amorphous metal(Al-Sm system).To a certain extent,it provides useful references for experimental and theoretical research of these materials.In chapter 1,we briefly introduced some basic concepts and computational methods of quantum chemistry,as well as the methods of crystal structure search.In chapter 2,we introduced the background knowledge of lithium battery and current research status of various cathode materials.In chapter 3,a Fe-P network scheme in searching for LiFePO4 crystal structures were introduced,and a large number of low-energy structures were acquired,which allowed us to build a comprehensive crystal structure database.The search scheme introduced here can also be extended to other similar systems.In chapter 4,the previous search results were classified based on the Fe-P network.The energy,volume,voltage and valence in each Li composition of LixFePO4(x=1～1)with different Fe-P networks were calculated.In chapter 5,we investigated the phase transitions in LixFeSiO4(x=1)system.A structural rule of low-energy LiFeSiO4 configurations were used to investigate the Li-Fe site exchange mechanism and a new cycled phase of experimental structure were proposed.We also compared the original delithiated LiFeSiO4 structures with the substituted ones from LiFePO4 and proposed an extra phase transition mechanism between the two types to explain the capacity loss.In chapter 6,amorphous metal materials were introduced and the devitrified process of Al-Sm model system were investigated based on the medium range order of Sm-Sm network using molecular dynamics simulation.In chapter 7,we summarized the work in this thesis.