Preparation And Lithium Storage Performances Of Sn-based And Si-based Anode Materials For Lithium Ion Batteries

Great efforts are focused on exploiting high-capacity materials to substitute for the commercialized graphite anodes with a low theoretical capacity(only 372 mAh g-1)and unsatisfactory high-rate performances.An ideal alternative is Sn or Si with the as-known the highest theoretical capacity(990 mAh g-1 for Li4.4Sn and over 3500 mAh g-1 for Lil5Si4).However,the large specific volume change in Sn and Si materials that occur during charge/discharge processes leads to rapid pulverization of the electrode,resulting in poor capacity retention upon extended cycling.Simultaneously,the poor electronic conductivity of Si seriously hampered its lithium storage performances and practical applications.Preparing nanomaterials,film materials or mixing them with active/inactive materials can effectively solve these troublesome obstacles.Therefore,Sn-based and Si-based micro/nano-complex or nanocomposites were synthesized as high-performanced anode materials for lithium ion batteries in this dissertation.The lithium storage behaviors were investigated systematically and in depth by several characterizations and electrochemical tests.(1)PANI@Sn@Cu precursors were fabricated first by electro-less depositing and oxidative polymerization,and transformed to C@SnCu nanocomposites after annealing at high termperatures.The C@SnCu products have complete core-shell nanostructures and good particle distributions.Compared with the products by ball milling and calcination,C@SnCu nanocomposites demonstrated good Li+storage capability and high rate capabilities.(2)3D macroporous Sn-Ag film were prepared through electro-less depositing on Cu film substrate.It found tha different plating time resulted in different pore-structured Sn-Ag thin film electrodes.Sample SA-2 possesses a reanonable three-dimensional porous structure and delivered a reversible capacity of 583mAh g-1 after 100 cycles without obvious damagement to the original structure.(3)Graphene@Cu2O and graphene@Sn composites were prepared by the solvothermal reduction and NaBH4 reduction method,respectively.Cuprous oxide evenly distributed in the graphene layer and cuprous oxide particle size was about 10 nm.Further,graphene@Cu2O composites were used as the Cu soruce to prepare graphene@SnCu materials through hydrogen reduction,chemical plating and heat treatment.Compared pure graphene and tin material,both graphene@SnCu and graphene@Sn exhibited better electrochemical performance due to the favorable help of Cu and grephene.(4)Micro/nano-complex-structure SiOx-PANI-Ag compsites were fabricated via magnesiothermic reduction and in-situ polymerization by using SiO2 microparticles.The internal structure of SiOx can be optimized by changing SiO2/Mg ratios.The SiOx(SiO2-1.8 Mg)composites have homogeneously-embedded Si nanocrystals(?5 nm)and nanopores(?3 nm)in amorphous SiOx matrix.When further modified by PANI and Ag,the obtained SiOx-PANI-Ag micron-composites exhibited better cycling performances(with a reversible capacity of 1149 mAh g-1 after 100 cycles)in comparison with SiOx-based materials in other works.