Preparation And Electrochemical Performance Of Silicon/carbon Anode Materials For Li-ion Battery

In recent years,silicon（Si）has been considered as the most promising anode material for the next generation of lithium-ion batteries due to its high theoretical capacity,suitable working potential and abundant resources.However,some flaws,such as,the low intrinsic conductivity and the huge volume expansion of silicon anode,limit the industrial application of silica-based anode materials in lithium ion batteries.Therefore,in order to solve the above problems,we make great efforts to design and prepare silicon materials with different structures,and compound them with carbon materials and metal oxides to improve the flaws of silicon-based anode and obtain excellent electrochemical performance.The research contents are as follows:（1）A new core-shell silicon carbon composite（SC-NF-0.24）was prepared by simple coaxial nozzle electrostatic spinning technology and calcination process,and it was prepared into self-supporting electrodes.It is found that the Si nanoparticles can be effectively encapsulated inside the carbon fibers,which can not only effectively alleviate the volume expansion of Si,but also improve the electrical conductivity of the material.The electrochemical test results showed that SC-NF-0.24 composite has excellent electrochemical properties.At the current density of 0.5 A/g,SC-NF-0.24 has an initial discharge capacity of 1441 mAh/g,with an initial Coulomb efficiency of70.5%.The capacity retention rate is 76.9%after 200 cycles.（2）Spherical silicon carbon composite（SCM）with micro/nano structure was prepared by in-situ polymerization and electrostatic spray methods.The results show that the silicon nanoparticles were coated by a nitrogen-doped carbon layer（Si@NC）to alleviate the volume expansion of silicon and enhance the electrical conductivity of the material,and then encapsulated in a three-dimensional carbon framework（SCM）to further improve the overall structural stability.The electrochemical test results show that SCM composite has excellent cycling and rate properties.At a current density of0.2 A/g,SCM composite possesses an initial discharge specific capacity of 1652 mAh/g,with an initial coulomb efficiency of 72.1%,and shows a reversible capacity of 746mAh/g after 200 cycles,with a capacity retention rate of 73.2%.（3）Base on the principle of synergistic effect,the hollow Si@TiO₂/rGO composite was synthesized by sol-gel and freeze-drying methods.It is found that the hollow silicon in Si@TiO₂/rGO composite has a large cavity,which can reserve buffer space for the huge volume expansion of Si.Meanwhile,TiO₂ coating layer can inhibit outward volume expansion of Si and maintain the structural integrity.In addition,the thin layer rGO can further improve the conductivity of composite and absorb the volumetric expansion stress of Si.The electrochemical test results show that Si@TiO₂/rGO composite has high specific capacity and good cyclic stability.At the current density of0.2 A/g,Si@TiO₂/rGO composite displays a specific discharge capacity of 1198 mAh/g,with an initial coulomb efficiency of 73%.Meanwhile,Si@TiO₂/rGO composite shows a reversible capacity of 961 mAh/g after 150 cycles,with a capacity retention rate of 79%.