| With the development of electric vehicles,hybrid vehicles,and portable electronic devices,this type of mobile power device requires a large capacity compact secondary battery to drive.Developing anode materials with higher capacity than traditional graphite negative electrodes is necessary.Silicon is recognized as one of the most attractive negative electrode materials in the next generation of lithium-ion batteries due to its abundant natural reserves,environmental friendliness,and high theoretical specific capacity of 4200 m Ah g-1(more than 10 times that of traditional graphite negative electrodes(372 m Ah g-1).However,the practical application of silicon materials is largely limited by volume expansion,unstable SEI growth,low conductivity,and low lithium ion diffusion coefficient.In this thesis,a series of silicon-carbon composites were prepared by modifying the surface of silicon particles using different carbon layers and cladding sequences,and the study of their lithium storage performance proved that the external carbon layer modulation of silicon/carbon（Si/C）composites can effectively improve their structural stability and cycling stability,and the carbon materials,because of their high mechanical stability and electrical conductivity,can give full play to their respective advantages when compounded with silicon materials.The main research contents is as follows three parts:1.silicon nanoparticles are encapsulated in a carbon shell derived from the precursor ZIF-67 by a facile chemical precipitation method.The most important core of this work is modulating the degree of dispersion of the silicon particles by adding a surfactant and sonicating to fully dissociate the silicon particles.As expected,the Si@c-ZIF composite electrode exhibits a higher initial coulombic efficiency（～70%）compared to bare silicon,and this excellent electrochemical performance is attributed to the in situ synthesis of ZIF-67 to produce a porous carbon-covered silicon composite with a core-shell structure（denoted as Si@c-ZIF）.The Si@c-ZIF has a large number of pores,which can provide channels for Li+infiltration and diffusion,and the extra space between the internal silicon nanoparticles and the porous carbon shell provides a buffer space for the volume expansion of silicon particles,thus avoiding the crushing of silicon nanoparticles.2.Polyacrylonitrile fibers containing Si@ZIF-67 are fabricated by electrostatic spinning method,and then pre-oxidized and carbonized to synthesize porous carbon nanofiber-loaded silicon-carbon composites（denoted as Si@c-ZIF@CNFs）.The initial specific capacity of 853 m Ah g-1at a current density of 1.0 A g-1still has a specific capacity of 281.7 m Ah g-1after 1000 cycles.The Si@c-ZIF@CNFs reveal excellent cycling and multiplicative performance attribute to the MOF structure limiting the silicon volume expansion and the electrospun CNFs with a network structure acting as fast electron transport channels,and this composite structure can mitigate the direct contact generated by the silicon particles stress concentration and ensure the structural integrity of the electrode.3.silicon/carbon（Si@C）composites with a core-shell structure were synthesized by a simple organic carbon source pyrolysis method,with Si nanoparticles as the core and a porous amorphous carbon layer formed by citric acid pyrolysis as the shell.MOFs-derived silicon/carbon（Si@C）particles encapsulated in a carbon shell were prepared by hydrothermal method to form a rhombic dodecahedral core-shell double carbon layer structure（denoted as Si@C-CA@c-ZIF）.The initial specific capacity of Si@C-CA@c-ZIF在1.0 A g-1current density is 1224.6 m Ah g-1.After 1000 cycles,its discharge specific capacity can still reach 704 m Ah g-1.It exhibits higher initial coulombic efficiency（about72%）,higher reversible capacity retention,and excellent rate capability. |
