Preparation Of Biomass Carbon-coated Modified Silicon Anode Material And Research On Its Battery Performanc

As an efficient and convenient energy storage device,the demand for lithium-ion batteries in the new era energy market is increasing day by day.However,the capacity of graphite anode used in commercial lithium-ion batteries is very limited.It is urgent to find a new anode material to promote the development of high energy density lithium-ion batteries.Silicon is considered as the most potential new generation anode material for lithium storage devices due to its high theoretical specific capacity,suitable operating voltage,abundant reserves and environmental friendliness.However,the serious volume effect and poor conductivity of silicon in the process of charge and discharge seriously hinder the effective exertion of its advantages.In addition,practical problems such as high production cost and complex manufacturing process also restrict the commercial development of silicon anode materials.Aiming at the current scientific and practical problems of Si,this paper selects low-cost and environment-friendly biomass materials and novel and simple synthetic methods to modify silicon materials,prepares silicon/biomass carbon composite cathode materials with excellent performance,deeply analyzes the physical and chemical properties and electrochemical properties of the composite materials,and comprehensively evaluates the application prospect of silicon/biomass carbon composites.The specific research contents are as follows:（1）Preparation and performance study of high-performance Si@NN-BC composites assisted by soybean.Inspired by the honeycomb structure of frozen tofu,this chapter takes soybean rich in protein and low price as the natural source of C and N,and applies the traditional preparation process of frozen tofu to nano silicon materials to prepare an unique“Silicon Tofu”structure,realizing the interesting idea of producing silicon-based anode materials for high-performance lithium-ion batteries in the kitchen.At the same time,the relationship between the micro morphology,material composition,carbon content and electrochemical properties of the synthetic materials was explored through systematic characterization.It was confirmed that the three-dimensional N-doped carbon network derived from tofu can not only effectively prevent the aggregation of silicon particles,but also enhance the conductivity of the materials and provide more Li⁺active sites for the materials.Based on the synergistic enhancement effect of natural porous structure and nitrogen doping,the initial coulomb efficiency of the optimized Si@NN-BC-25 material is as high as 83.6%.It can still maintain a high reversible specific capacity of 894.2 m Ah g^-1at a high current of 2 A g^-1.After 300cycles at 1 A g^-1,it can still retain a capacity of 731.6 m Ah g^-1and has a high capacity retention rate.This work provides a new method for preparing Si/C composites with low-cost and high performance.（2）Preparation and properties study of pSi@NC composites modified by gelatin and sodium alginate.To further reduce the cost,this chapter selects aluminum/silicon alloy powder(Al-Si₂₀)with lower cost as silicon precursor,etches the aluminum phase to further obtain the micron porous silicon（pSi）raw material,and then uses the green low-cost,water-soluble and strong adhesion gelatin and sodium alginate to coat and modify the pSi to prepare the good performance pSi@NC composites.Combined with the systematic characterization method,the morphology and composition of the prepared materials were obtained,and the optimal raw material ratio was determined by electrochemical test.This experiment shows that the N-doped carbon coating derived from gelatin and sodium alginate can not only effectively inhibit the occurrence of side reactions,but also improve the electronic/ionic conductivity of the material.The optimized pSi@NC-1 composite was cycled 200 times at a current of 1 A g^-1,the capacity was maintained at 509.8 m Ah g^-1,and the capacity retention rate was as high as87.6%.This chapter lays an experimental foundation for the study of carbon coating modification of micron porous silicon.（3）One step synthesis of high-performance 3D pSi@rGO@NC/Cu structure electrode and its properties study.Based on the research of the previous chapter,this chapter optimized the experimental scheme by adding monolayer graphene oxide（GO）and Cu（NO₃）₂,and constructed a 3D electrode without conductive agent and binder.The morphology,chemical composition and pore size distribution of the synthetic materials were determined by a series of characterization methods.It is confirmed that the carbon mesh derived from GE and SA cooperates with the highly conductive rGO sheet and Cu particles to obtain excellent cycle performance and rate performance by maintaining the interface stability of electrode structure and providing more continuous e^-/Li⁺transport channels.The optimized pSi@rGO@NC/Cu-2 3D structure electrode can still show a high reversible specific capacity of 992.2 m Ah g^-1at a high current density of 5 A g^-1,and can still retain a specific capacity of 1007.1 m Ah g^-1after 200cycles at a current of 1 A g^-1.Compared with the traditional pSi electrode,the electrochemical performance is significantly improved.This method provides a new solution for the construction of Si/C composite anode materials with high tap density and lithium-ion batteries with high energy density.