Fabrication And Electrochemical Performance Of Two-Dimensional Material/Nano-silicon Composite Anode With Hierarchical Structure

Silicon is considered to be the most promising next-generation lithium-ion battery anode material because of its high theoretical specific capacity(4200 mAh/g)low lithium insertion voltage and abundant resources.However,silicon anode has a large volume expansion problem during the electrochemical charge/discharge cycle process,which causes the problem of unstable cycling performance and further limits its practical application in lithium-ion batteries.In this thesis,new silicon-based anode materials were prepared by different process methods and control methods.A two-dimensional material conductive network framework was constructed and silicon is controllably embedded in the two-dimensional material network framework.The reasonable material structure effectively alleviates the problem of silicon expansion during the charge/discharge process.At the same time,many characterization methods were applied to test the prepared materials.The morphological changes and lithium-ion storage mechanism of the anode materials during the cycling process were explored.The main research contents and results are as follows:1.With the super-permeability of supercritical carbon dioxide,graphite was first stripped into two-dimensional foldable graphite sheet with high mechanical strength.Meanwhlie,supercritical fluids with the high diffusivity is used to uniformly disperse nano-silicon powder and carbon nanotubes between foldable graphite layers.With the help of supercritical fluid,all the components were controllably assembled into a silicon-based anode material with a multi-level conductive network.The conductive network constructed by two-dimensional folded graphite and carbon nanotubes accelerates the electrons and ions transmission rate in the overall electrode and alleviates the expansion problem of nano-silicon powder.The electrochemical performance test of the prepared material shows that the material has excellent cycle performance and rate performance.2.The two-dimensional material MXene is widely concerned in the field of energy storage because of its metal-level conductivity and rich surface chemistry.In this work,the nano-silica powder was modified with PDDA to make the surface positively charged.The surface of MXene etched from MAX has a variety of groups attached to it,so the surface of MXene is negatively charged.MXene and modified nano-silica powder were prepared by electrostatic self-assembly in liquid-phase conditions.The prepared MXene-Si composite material has three-dimensional conductive network.The electrochemical characterization proved that the prepared material had excellent electrochemical performance.