Preparation And Lithium Storage Performance Of Palygorskite-based Silicon-Carbon Composite

At present,graphite,which is a commercial anode material for lithium ion batteries,has a theoretical specific capacity of only 372 mAh g^-1,which is far from meeting people’s needs for high energy density lithium ion batteries.In recent years,silicon-based anode materials are considered to be the most promising anodes for new-generation lithium-ion batteries due to their high theoretical specific capacity(～4200 mAh g^-1)and low lithium insertion potential（about 0.4 V）.Material system.However,silicon undergoes a huge volume expansion（～300%）during the lithium insertion process,which easily causes the structural integrity of the material to be destroyed,and continuously forms an unstable solid electrolyte（SEI）film.The capacity decays and the Coulomb efficiency is low during electrode cycling The adverse effects such as poor cycle stability have seriously hindered the practical progress of silicon-based anode materials.Based on this,in order to obtain high-performance silicon-based anode materials,this paper selects inexpensive palygorskite as the silicon source and graphene or gum arabic as the carbon source to construct a variety of silicon-carbon composite materials,and studies its structure-activity relationship.The main content of the paper is as follows:1.The cheap and easily available palygorskite was selected as the silicon source,and nano-sized silicon particles were successfully prepared by the magnesium thermal reduction method.The raw material ratio（1:5-1:1）and heat treatment temperature（850-1050℃）were studied.,Holding time（4-8 hours）and other preparation process parameters affect the morphology of the product silicon and lithium storage performance,and optimize the best preparation process.The results show that when the mass ratio of palygorskite and magnesium powder is 1:3,and the magnesium thermal reduction treatment is performed at 950℃for 5 hours,the prepared nano-silicon powder has the best lithium storage performance:at a current density of 200 mA g^-1,the first reversible specific capacity can reach2286.1mAh g^-1,and the first Coulomb efficiency is 81%.2.In order to improve the cycle stability of the prepared silicon anode,using graphene oxide（GO）as a carbon source,a composite material of silicon and reduced graphene oxide Si/rGO was prepared,and the amount of GO added,the solvothermal coating process,The influence of the subsequent calcination heat treatment temperature on the phase composition,morphology and structure of the composite material and the electrochemical lithium storage performance.The results show that the Si/rGO nanocomposite obtained by adding GO at 60wt.%,Heat-treated at 180℃and calcined at 500℃has good cycle stability:at a current density of 200 mA g^-1 After 60 cycles,the reversible capacity can maintain 565.5mAh g^-1,which is significantly higher than pure silicon.The improvement of its cycle stability is due to the combination of graphene,which not only improves the conductivity of the electrode,but also the mechanical flexibility of the graphene effectively relieves the volume effect during the charge and discharge process and enhances the structural stability of the electrode.3.In order to further improve the electrochemical performance of the silicon negative electrode,a natural polymer material Gum Arabic（GA）was used as a carbon source,and the silicon nanoparticles were carbon-coated by a solvothermal method and a high-temperature carbonization treatment to successfully prepare a silicon/carbon composite.Materials,and the effects of preparation process parameters such as GA addition amount,solvothermal temperature,and calcination temperature on the composition,morphology,structure,and electrochemical lithium storage performance of composite materials were investigated.The experimental results show that when the additional GA content is 40wt.%,The solvothermal temperature is 160℃,and the calcination temperature is 700℃,the silicon-carbon composite material has the best cycle stability:at a current density of 200 mA g^-1,The first reversible specific capacity is 1446.8 mAh g^-1,the first efficiency is74.5%,the reversible specific capacity can still be maintained at 652.1 mAh g^-1after 150 cycles.Its performance improvement is due to the strong interaction between the carbon source gum arabic and silicon particles,which helps to improve the electrical contact between the coated carbon layer and the silicon particles and buffers the silicon volume effect.