Structure Design And Application Of Silicon/carbon Anode For Lithium-ion Batteries

Lithium-ion batteries are thought to be an efficient and convenient energy storage equipment,but they are restricted by graphite-based anodes,which have a difficulty for meeting the demand for high energy density.Silicon materials are widely regarded as one of the most promising anode materials owing to their high theoretical capacity,suitable charge/discharge voltage platform,resource abundance and environment friendliness.However,there exist some obstacles for silicon anodes such as volume expansion and poor electrical conductivity.In addition,the high cost of nano-sized silicon also greatly limits its practical application.Therefore,developing the improved silicon anodes with low cost and high performance is significant for the commercial application of the advanced lithium-ion batteries.In this thesis,in order to prepare low-cost and high-performance silicon/carbon(Si/C)composites,we designed and constructed Si/C composites by different methods.The low-cost photovoltaic waste silicon powder was used as raw materials after simple purification and ball-milling,and the nano-sized silicon particles are obtained which can satisfy the demand for silicon-based anode materials of lithium-ion batteries.Then,we designed and successfully prepared a series of Si/C composites with different structures,which can not only improve the conductivity,but also relieve the volume expansion during cycles.We also analyze the structure and physical chemical characteristics of the above materials,and test their electrochemical performance in lithium ion batteries.The results of the research are listed as follows:(1)In this work,it proposed a self-assembly CaCO3 template method to prepare Si/C composite,which combines self-assembly,pyrolysis carbonization and chemical etching.The Si@Voids@PC anode shows excellent cyclic stability and good reversible capacity,with the reversible capacity up to 1527 mAh g-1 after 200 cycles with an initial discharge specific capacity of 3060.6 mAh g-1 and ICE of 74.4%,which is better than most reported results based on recovered silicon.(2)A simple surface-engineering-assisted method was adopted to successfully prepare the Si/C anode with a uniform carbon shell.In the process,the recovered waste silicon particles(RWSi)were modified by the silane coupling agent(kh550)(m-RWSi),and the PMMA was formed by the polymerization on the surface of the RWSi particles.The uniform carbon coating layer obtained by PMMA pyrolysis with high graphitization degree and low specific surface area,which can not only improve the structural stability,reduce the mechanical stress caused by volume expansion,but also improve the conductivity.The results showed that the specific capacity of the m-RWSi@PMMA-C anode was 1083 mAh g-1 after 200 cycles with an ICE of 75.6%,as well as improved rate performance.(3)Besides,the CNTs enhanced PMMA-derived carbon coating recovered waste silicon particles as Si/C anodes are also prepared.At the current density of 200 mA g-1,the initial specific capacity of Si/CNTs@PMMA-C is 3732.7 mAh g-1 and the ICE is 78.2%.After 200th cycle,the specific capacity can still be maintained at 1024.8 mAh g-1.In addition,when the current density is 500 mA g-1,it also shows excellent long cycle life with a high specific capacity of 795.5 mAh g-1 after 500 cycles.The full cell with the Si/CNTs@PMMA-C as anode and the commercial LiCoO2 as cathode exhibits a high energy density and huge application potential.