Study On The Preparation And Lithium Storage Mechanism Of Silicon Carbon Composites With High Specific Energy

In order to overcome the shortcomings of pure silicon（Si）and silicon oxide（SiO_x）electrode materials such as severe volume expansion and poor electrical conductivity In this thesis,Siand SiO_x are used as the raw materials to construct various carbon-based composite materials,and the additive amount of carbon-based material on the electrochemical properties of composite materials is discussed.SiMP/G-6 composites were prepared by ball milling-annealing method using micro-silicon（SiMP）and graphite（G）as raw materials.The first coulombic efficiency and the capacity retention after 200 cycles were 70%and 44%,respectively.On this basis,SiMP/G/SC and SiMP/G/PC composites were prepared with sucrose（SC）and pitch（PC）as carbon sources,respectively.The reversible capacities of SiMP/G/SC and SiMP/G/PC composites were 417 m Ah g^-1 and 449 m Ah g^-1 after 200cycles at the current density of 500 m A g^-1,respectively,and the capacity retention was 85%and 87.7%,respectively.Subsequently,the SiNP/G/SC-5 and SiNP/G/PC-7composites prepared by changing micro-silicon to nano-silicon（SiNP）exhibit the initial coulombic efficiencies of 88.9%and 82%at 500 m A g^-1,respectively.The reversible capacities after 200 cycles are 465 m Ah g^-1 and 442 m Ah g^-1,respectively.Finally,SiNP/G/N-PC composites were prepared.The initial coulombic efficiency was 94%,which was improved compared with SiNP/G/PC-7.It shows that the doping of N element can not only maintain the original advantages of pitch pyrolytic carbon,but also provide lattice defects to improve lithium storage performance.SiO_x/G-6 composites were successfully prepared by the ball milling-pyrolysis method using silicon oxide（SiO_x）as silicon source.The initial coulombic efficiency and the capacity retention of SiO_x/G-6 after 200 cycles at 500 m A g^-1 were 81%and55%,respectively.The as-prepared SiO_x/G/SC-3 composite exhibits an initial coulombic efficiency of 78%at the current density of 500 m A g^-1.After 200 cycles,the reversible capacity remains 607 m Ah g^-1,and the capacity retention is 76.8%.The initial coulombic efficiency of SiO_x/G/PC-4 composite was 73.9%at the current density of 500 m A g^-1.The capacity retention was 82.6%after 200 cycles,and the reversible capacity of 446 m Ah g^-1 could be retained after 10 cycles at a high current density of 800 m A g^-1.Finally,SiO_x/G/N-PC composites were prepared,and the initial coulombic efficiency was 70.3%at the current density of 500 m A g^-1.After 200 cycles,the capacity retention rate was 97%,which was improved compared to SiO_x/G/PC-4.This paper has 99 figures,12 tables and 115 references.