Preparation Of Nanometer Silicon-based Composite Materials And Study On Electrode Performance

Compared with other batteries,lithium-ion batteries have many advantages,such as high discharge capacity,excellent cycle performance,simple preparation process,and green and pollution-free,and have been widely used in many energy fields.Silicon material has a very high theoretical specific capacity（4200 mAh/g）,and it is environmentally friendly and has a large amount of earth.However,the volume expansion phenomenon of the battery during the charge and discharge process hinders the application of electrode materials.Commercial carbon materials have good electrical conductivity,good ductility,and good stability,so they are used as“buffering materials”to form composite materials.In addition,in the electrochemical reaction,the lithium insertion potentials of silicon and carbon materials are almost the same,and the combination of the two materials can obtain a lithium ion battery electrode material with high capacity and excellent cycle performance.Therefore,in this thesis,nano-silicon materials are used as silicon sources,and dopamine,phenolic resin,and PVDF are used as carbon sources to directly cover silicon-carbon composite materials.The silicon-carbon composite material is obtained as follows:Using dopamine,phenolic resin,and PVDF as carbon sources,the surface of nano-sized silicon particles was coated with a carbon source by a solvothermal method,and silicon-carbon composite materials were obtained after high-temperature carbonization.Among them,the carbon source of phenolic resin is excellent.When the current density is 0.1 A g^-1,the specific capacity of the composite material is 1280.8mAh g^-1.When the current density is increased to 5 A g^-1,the specific capacity of the electrode material is 176mAh.g^-1.After 300 cycles of maintaining a current density of 0.5 A g^-1,the capacity was 495.4 mAh g^-1,and the capacity retention rate was 37.5%.Using resorcinol and formaldehyde as raw materials,a phenolic resin was synthesized in situ by a solvothermal method,coated on the surface of nano-sized silicon particles,and then carbonized using a tube furnace to obtain a silicon-carbon composite material.With a resorcinol content of 0.3 g and a carbonization temperature of 900℃,a silicon core with a diameter of 50 nm and a carbon shell with a thickness of 15 nm were prepared.The material had a specific surface area of 135 m ² g^-1 and a multi-stage channel structure.When the current density is 0.1 A g^-1,the capacity is 2335.1mAh g^-1.After 50cycles,the specific capacity is still 1765.3 mAh g^-1,the capacity retention rate is 50.6%,and the increased current density is 5 A g^-1.The specific discharge capacity is 678.6 mAh g^-1,and the material still has a high capacity under large current density.