Preparation And Modification Of Silicon-based And Tin-based Anode Materials

As the energy crisis and environmental pollution problems become increasingly prominent,the development of new energy sources and solving storage problems have become the current main energy strategy.High-performance energy storage equipment is an important support for new energy utilization.Green and environmentally friendly lithium-ion batteries are used in many fields such as new energy vehicles,wind and solar power storage,signal base stations,small portable devices,etc.due to their advantages of suitable working voltage,long cycle life,high energy density,and low self-discharge.With the growth of economic demand,people have higher requirements for the energy density of lithium-ion batteries.The current commercial graphite anode materials are difficult to meet the requirements of high energy density due to their lower theoretical capacity,and high-capacity anode materials have become a trend.Silicon-based and tin-based anode materials have high theoretical specific capacity,low voltage platform,and abundant reserves,and there is a lot of room for development.However,the large volume expansion rate and poor conductivity seriously hinder the further development of the material.Therefore,in-depth research on how to solve the shortcomings of silicon-based and tin-based materials,such as poor cycleability and poor rate,has very important practical significance.In this thesis,by analyzing the failure mechanism of silicon-based and tin-based anode materials,the nano-silicon-porous carbon and SnO₂-porous carbon structures are designed to significantly improve the cycle performance and rate performance of silicon-based and tin-based anode materials.The main research results are summarized as follows:(1)Using starch as the raw material,porous starch is prepared by environmentally friendly biological enzymatic hydrolysis,and the single variable method is used to explore the optimal enzymatic hydrolysis amount,optimal enzymatic hydrolysis time,carbon layer effect and silicon content in the preparation process.Exploring the optimal conditions:the amount of enzymatic hydrolysis is 100:5,and the optimal enzymatic hydrolysis time is 12h.(2)The porous starch and nano silicon are encapsulated and carbonized to prepare a silicon-carbon composite material.The conductive framework of porous carbon,the volume expansion buffer,the promotion of ion transport and the protection of the carbon layer,make the electrochemical performance of the silicon-based material Has been greatly improved.With the increase in silicon content,the capacity of silicon-carbon composites has steadily increased.For a composite material with a silicon content of 30%,at a current density of 0.2 A g^-1,the initial reversible capacity of the composite material reaches 1490 m Ah g^-1,and the capacity is still 850 m Ahg^-1 after100 cycles.(3)SnO₂ with a small size is introduced into the porous starch and encapsulated to prepare a porous carbon-SnO₂ composite material,which effectively solves the problem of using the micropores of the porous starch.Due to the synergistic effect of favorable factors such as nitrogen doping,porous structure,Sn-O-C bond and small-sized SnO₂nanoparticles,the electrochemical performance of the material is greatly improved.The PSC-12/SnO₂/C composite material is cycled 100 times under the condition of 0.2 A g^-1 in the lithium ion battery,and the specific capacity reaches 700 m Ah g^-1,and the cycle has 320 m Ah g^-1 under the condition of 5 Ag^-1.