Preparation Of Silicon/Carbon Anode Materials Based On Crystalline Silicon Waste For Lithium-Ion Storage

With the rapid economic development,the consumption of traditional fossil energy has increased sharply,which has further increased the shortage of energy resources and the crisis of environmental pollution.Therefore,the search for renewable,non-polluting and clean energy has become a popular topic.New energy has the advantages of clean and renewable,but it has the shortcomings of intermittent and unstable supply,which makes it difficult to continuously supply energy.It is very necessary to develop new electrochemical energy storage devices for this problem.Lithium-ion batteries have been widely used as energy storage devices in everyday life,with the benefits of both high energy density and long cycle life.However,the current performance of lithium-ion batteries can no longer meet people’s needs,and the development of rationally designed new anode materials to improve the performance of lithium batteries has become a core research topic.With its high specific capacity,abundant natural reserves and environmental friendliness,silica-based materials are regarded as the best candidates for next-generation lithium-ion battery anodes.However,silicon-based materials have poor semiconductor properties,poor conductivity and severe volume expansion during electrochemical processes,resulting in rapid battery capacity decay and greatly reduced cycle life.At the same time,the rapid development of the photovoltaic industry in recent years has left behind a large number of silicon-based solar cells,which have become an important source of elemental silicon.Based on this,this thesis uses crystalline silicon cutting waste as the silicon source,and proposes a strategy of silicon-carbon composites to improve the conductivity and volume expansion of silicon-based substrates.The specific research contents are as follows.（1）Pretreatment of the scrap silicon（PS-Si）was prepared by simple pretreatment method,and its structure was characterized and analyzed in detail by SEM,XRD and other tests.The poor performance of the scrap silicon was analysed by electrochemical tests and attributed to the volume expansion of the material itself.It was proposed that C_X（X=EB,PPy,G）be used to form a dense carbon layer on the surface of the silicon to relieve the stress generated by the silicon during charging and discharging,which leads to the chalking and rupture of the electrode material,reducing the capacity decay and furthermore also enhancing the conductivity of the monomeric silicon.（2）Scrap silicon has the characteristics of low cost and environmental protection.Using pyrrole as the precursor of carbon materials,pyrrole is uniformly coated on the silicon surface by chemical oxidation polymerization,and annealed in nitrogen atmosphere,and then the FP-Si@C_PPyelectrode material was successfully prepared.The morphology and structure of the material were determined by XRD,Raman,TEM and other physical property characterization methods.The FP-Si@C_PPy composites have more defects,which provide more reaction sites for Li ions.The composite material has more defects,providing more reaction sites for lithium ions.Larger surface area can increase deintercalation sites and enhance electrochemical performance.At the same time,the presence of the mesoporous structure provides a transport path and reduces the resistance during the lithium ion transmission process.The FP-Si@C_PPy electrodes show a high reversible specific capacity with a first effect of 58%,and the specific capacity of the FP-Si@C_PPy-2 electrode is 460 m Ah g^-1 after 100 cycles.Moreover,the excellent performance of the FP-Si@C_PPyelectrodes in electrochemical energy storage were quantitatively analyzed by calculating the lithium-ion diffusion coefficient,with shorter diffusion time and higher lithium-ion transport kinetics.It provides an effective method to solve the capacity fading caused by the volume expansion of silicon in the process of charging and discharging.（3）In order to seek the direction of simple compounding process,the work of compounding glucose solution with PS-Si through physical mixing followed by freeze-drying has been carried out.The FP-Si@C_g composite was characterized by XRD and other physical properties,which proved that the silicon-carbon composite was successful,and its structure and composition were analyzed.By coating the silicon surface with carbon,the volume expansion rate of silicon is reduced,the specific surface area is increased,and the ion transport efficiency is improved.The electrochemical performance of the FP-Si@C_g composite assembled half-cell was further tested.Compared with PS-Si,FP-Si@C_g has a shorter diffusion time during lithium-ion transport.At a current density of 0.1 A g^-1,the specific capacity can still retain about 700 m Ah g^-1 after 100 cycles.（4）Carbon materials derived from natural biomass have their own unique structure and low price and environmental protection characteristics,with excrementum biowaste（EB）as the precursor of carbon materials and PS-Si,the FP-Si@C_EB composite materials are characterized by SEM,TEM,XRD,etc.,and determine the morphology and structure;the composite materials are prepared to produce silicon-carbon composite electrode materials with good performance,and the electrochemical properties are studied,and at the different rate of charge and discharge,after 100cycles,the reversible capacity reached 450 m Ah g^-1.The role of C_EB in electrochemical energy storage was also studied by quantitatively analyzing the storage behavior and diffusion kinetics of FP-Si@C_EB in lithium-ion batteries.This work not only provides a method for the effective use of waste silicon,while the biomass carbon source reduces the problem of ecological resource waste,it has also promoted the development of high-capacity anode materials for green energy storage.