Preparation Of Silicon-based Anode Materials Based On Surface Modification For Lithium-ion Bettaries

In recent years,the electric Vehicle?EV?industry develops rapidly,the EV with long endurance mileage propose a higher requirement to energy density and cycle life of lithium-ion batteries?LIBs?.Silicon-based anode,as next-generation anode material for LIBs,possesses extreme high specific capacity compared to commercial graphite anode.However,silicon anode suffers drastically volume expansion during lithiation processes,which cause fracture and pulverization of bulk silicon,destruction of electrode structure and repeated generation of solid electrolyte interface?SEI?layers,hindering practical application of silicon-based anode materials.In this paper,silane coupling agent is used to modify the surface of different silicon materials,and different kinds of functional groups are connected on the surface of the silicon materials.By using the reactivity of functional groups,TS-P-Si composites and MCMB@Si@C composites are prepared,and their structures are optimized to improve the electrochemical performance.In addition,this paper returns to the surface modification itself and studies the lithium properties of nano-silicon modified by hydroxyl group and alkyl group respectively and the related mechanism.The innovative results obtained in this paper as follows:?1?The surface oxidation rich in hydroxyl of silicon material was carried out by a mixture of sulfuric acid and hydrogen peroxide.Different functional groups are connected on the surface of silicon anode by coupling effect between silane coupling agent and hydrogen on silicon surface.Different silicon-based composites can be prepared in the effect of chemical properties of functional groups?2?TS-P-Si composites were prepared by reducing the primary particle size of porous silicon,constructing the surface oxide layer,depositing silver nanoparticles and acetylene pyrolysis carbon coating.As anode material of LIBs,TS-P-Si composite material has excellent electrochemical performance because of its unique treble-shell structure,which has stronger structural stability and conductivity.?3?Si-OH and MCMB-COOH were obtained by surface oxidation treatment of silicon nanoparticles and MCMB.MCMB@Si@C composites are synthesized by a simple wet-chemical method and subsequent thermal decomposition of acetylene with Si-OH and MCMB-COOH used as precursors and aminopropyl triethoxy silane as binder.MCMB@Si@C composites show excellent electrochemical performance as anode materials of LIBs.?4?A promoting effect of hydroxyls on silicon surface to the decomposition of electrolyte is discovered by comparing the performance of silicon-hydroxyl?Si-OH?and silicon-alkyl?Si-C3H7?electrodes.X-ray photoelectron spectroscopy?XPS?characterizations of both SEI layers demonstrate the influencing mechanism that hydroxyls can react with LiPF₆ to form POF₃,which further induces the decomposition of electrolyte solution.This study provides a new consideration that limiting the amount of hydroxyls on silicon surface in an appropriate range is significant to the electrochemical performance of silicon-based anode materials.