High Capacity Silicon-based Anode Materials For Lithium Ion Battery

Silicon has been widely recognized to be the most promising anode for the next generation Li-ion battery due to the high specific capacity,appropriate working potential and abundant resources.However,the inherent problems of volume variation and unstable SEI during cycling have hindered the practical application of Si-based anode materials.It is now well accepted that there are three main directions for future development of Si-based anode: Nano-Si/C composite material,SiO/C composite material and amorphous Si-base alloy.In particular for Nano-Si/C and SiO/C composite material,much efforts have been made to improve the electrochemical performances and they have now been practically used in small range of applications.There are mainly three parts in this thesis:(1)Size effect of Si particles on the electrochemical performances of Si/C composites anodes,focusing on the study of failure mechanism of Si/C composites embedded with Si with different particle size.(2)Structure evolution and its relevance to the electrochemical performances of the SiO/C composite materials.(3)Research on high capacity Si/C anode materials.The design development and modification of practical Si/C and SiO/C composites,and the construction of ton-scale production line.Four kinds of Si/C composite materials were obtained by heat treatment of the mixture of carbon precursor and Si with particle size of 30 nm,100 nm,500 nm,3 ?m.The size effect of Si in Si/C composite materials has been investigated.Nano-sized Si and Si/C composite with nano-sized Si demonstrate good capacity retention behavior.The generation and evolution of crack was explored by FIB and SEM to understand the failure mechanisms.Finally,the rate performance and fading mechanism of Si/C materials are further analyzed.Similar synthesis method has been applied to fabricate SiO/C composite materials using 3 ?m-SiO as precursor.The internal crack evolution and the structural changes of silicon oxide during cycling were studied.The experimental results show that the gradual change of the structure upon the electrochemical cycling.X-ray pair distribution function technique was employed to further investigate the structure evolution of micro-sized SiO during cycling.The structure and lithiation process of self-made 30-50 nm nano-SiO after heat treatment at different temperature were studied.A series of practical silicon-based anode materials has been designed with the knowledge gained from the aforementioned fundamental researches.With the designed capacity of 400-450 mAh/g,the optimized silicon-based anode material shows the capacity retention of 90% after 500 cycles.A 500 ton-scale production line for siliconbased anode material was constructed in Liyang,Jiangsu Province.