Preparation Of Silicon-carbon Composite And Study On Its Lithium Storage Properties

In order to achieve sustainable development and continue promote the energy transition and structural adjustment,the large-scale use of electric vehicles has become a priority for people.Batteries is the core of electric vehicles.Therefore,the recent research hotspot is looking for lithium-ion batteries with high energy density and long service life.Silicon-based anode materials have become the mainstream choice due to high theoretical capacity,rich resources,and low lithium insertion potential.However,it is inevitable that the electrode suffers from severe volume expansion,and the SEI film is unstable during cycling,which leads to decrease in capacity and a shorter cycle life.Nowadays,there are many strategies to solve this problems such as nano-silicon,porous silicon,and silicon carbon composites.This paper is mainly based on a multi-dimensional strategy to synthesize silicon-carbon composites with different coating types.The specific works are as follows:(1)We successfully prepared pinecone-like silicon carbon microsphere covered Al₂O₃ nano-petals(Si@C@Al₂O₃)through a simple self-assembly method.This material exhibited excellent electrochemical performance which rendered an ultra-large reversible capacity of1405 m Ah g^-1at a current density of 5 A g^-1 after 1000 cycles at 80^oC.Even at a high current density of 8 A g^-1,which still showed an excellent 1276 m A h g^-1.Such excellent performance was attributed to the double-layer protection of Al₂O₃nano-petals and carbon layer.The carbon layer could enhance the conductivity of the composite material and relieved the volume expansion of silicon.The Al₂O₃ nano-petals had abundant mesopores and sufficient mechanical strength which provided the faster ion diffusion path and maintain the stability of the structure.The most important was that under high temperature conditions,the electrode had the small the interface resistance and charge transfer resistance,which helped to improve the kinetics of the lithium ion storage process.(2)We successfully synthesized porous silicon-carbon composite(Porous Si@C)by using a simple method combining metal corrosion and solvothermal.The material exhibited excellent cycle stability and rate performance.At a current density of 200 m A g^-1,it had a reversible capacity of 2576.4 m A h g^-1 after 250 cycles.Even at a high current density of 5 A g^-1,it still showed a capacity of 826 m A h g^-1 after 700 cycles,which was mainly attributed to the integrity of composite structure,silicon was the main skeleton which provided a higher specific capacity;the coating of the carbon layer could not only improve the conductivity,but also relieve the volume expansion to some extent;the porous structure could shorten the lithium ion transmission path.Such a carefully designed structure lays the foundation for the commercial application of silicon-based materials.