Preparation Of Thin-layer Graphene-coated Silicon-based Composite Anode Materials By Mechanical Ball Milling And Its Lithium Storage Properties

With the continuous development of science and technology,the demand for high-capacity,high-stability,high-security battery products is also growing.The capacity of conventional anode material graphite has been developed to near theoretical values.At present,the mass specific capacity of the anode material of lithium ion batteries has been unable to meet the market demand.In order to increase the capacity of lithium-ion batteries,researchers are exploring new types of anode materials.Among them,silicon is used as a negative electrode material for lithium ion batteries,and its theoretical lithium insertion capacity is as high as 4200 m Ah g^-1.It is more than 10 times higher than the mass specific capacity of the traditional graphite anode material(the theoretical capacity of graphite is 372 m Ah g^-1),and it is the most potential lithium ion battery anode material in the future.However,in the process of charge and discharge,the volume expansion coefficient is larger and the conductivity is poor,which may generate an unstable SEI film,resulting in poor cycle stability and short service life.Based on the performance characteristics and existing problems of the above silicon-based anode materials,this paper mainly explores the modified silicon-based composite materials as the anode of lithium-ion batteries and its properties.In this paper,a simple mechanical ball milling method is used to prepare a thin layer of graphene-coated silicon-based composite anode material;the coating of thin layer graphene inhibits the volume expansion of silicon particles and further improves the conductivity,thereby effectively improving Cyclic stability and service life of silicon-based anode materials.details as follows:(1)Based on a simple mechanochemical approach,the first use of metal zinc particles as an auxiliary sacrificial reducing agent to prepare a core-shell silicon/graphene composite anode material with high specific capacity and good cycle stability(abbreviated as nuclear-Shell Si/r GO).The composition,structure,morphological characterization and electrochemical tests show that the core-shell Si/r GO composite composites have superior performance.It is charged and discharged at a current density of 200 m A g^-1,and is circulated for 200 cycles with a mass specific capacity of up to 767 m Ah g^-1.Charging and discharging were performed at a current density of 500 m A g^-1for 300 cycles,and the mass specific capacity was maintained at 548 m Ah g^-1.Through simple mechanical ball milling and the auxiliary action of metal zinc powder,the graphene oxide is uniformly coated on the surface of the silicon particles,and the metal zinc and its oxide form a certain vacancy after being etched by hydrochloric acid,which is a process of silicon expansion.The space is provided,and the penetration of the electrolyte is facilitated,and the active site of the material is increased,so that the lithium intercalation activity of the material is further increased.(2)Based on simple mechanical ball milling,the Si/Al₂O₃/RGO composite anode material with high magnification and high cycle stability was designed and prepared by the double coating strategy of Al₂O₃and RGO.A simple mechanical ball milling,PVP is used as a surfactant and a binder,and alumina and graphene are introduced as a buffer layer.The results show that the material is charged and discharged at a current density of 500 m A g^-1,and the mass specific capacity is as high as 852 m Ah g^-1after 200 cycles.(3)Based on a simple high-energy ball milling method,using micron silicon as a silicon source,polyvinylpyrrolidone(PVP)as a binder and carbon source,and assisting graphene-coated silicon nanoparticles,the design has a high specific capacity and high Cyclic stability of Si@C@RGO composites.The adhesion of PVP assists the uniform coating of graphene around the silicon particles and carbonization through high temperature to obtain Si@C@RGO composite.The results show that the material is charged and discharged at a current density of 500 m A g^-1,and the mass ratio of 300 cycles is up to 643m Ah g^-1.It is charged and discharged at a current density of 1000 m A g^-1,and the mass ratio of 500 cycles is up to 385 m Ah g^-1.(4)Si@RGO composite with high content,high magnification and high cycle stability was directly prepared by a simple high-energy ball milling method using micron silicon as the silicon source and a two-step ball milling route without surfactant.High-purity micron silicon was added to the ball mill tank,and anhydrous ethanol was added as a ball milling medium.The Si@RGO composite material is obtained by introducing a graphene ethanol solution by simple and efficient mechanical ball milling.The results show that the material is charged and discharged at a current density of 500 m A g^-1,and the mass ratio of the cycle is up to 824 m Ah g^-1.And charging and discharging under the current condition of 1000m A g^-1,the cycle mass ratio capacity is up to 638 m Ah g^-1.