Fabrication Of Si Nanoparticles-based Nanocomposites For Lithium Storage Application

Lithium-ion batteries（LIBs）are the most widely used secondary battery in twenty-first Century,due to its high energy density,higher operating voltage,limited self-discharging and low maintenance demand.It has been successfully applied to various industries such as electronics and electric vehicles etc.At present,the characteristics of high energy density,high power density and security are needed by electric vehicles and distributed energy storage industry.LIBs are still the main form of recent electrochemical energy storage although the research of Li-S and Li-O₂ batteries with higher energy density are in full force.The theoretical capacity of graphite(372 mAh g^-1)which is main commercial anode material used for LIBs is relatively low,which leads to the low specific capacity of battery and limits the application of LIBs in some fields.Si material is also an alternative anode material for LIBs because of its highest theoretical capacity(4200 mAh g^-1).The electrochemical potentials of Si is higher than Li metal,and certainly higher than lowest unoccupied molecular orbital（LUMO）of electrolytes,which will lead to formation of the SEI film on its surface during charging process.However,successful applications of silicon anode have been impeded by large volume expansion（360%）with lithiation,which accelerate electrode collapse and capacity fading with exacerbating irreversible side reactions.Recently,there have been tremendous studies aiming to solve this problem.The strategies developed include utilizing nanoscale silicon,compositing with stress-relief buffer matrix and constructing physical compartment to accommodate volume expansion.In this paper,we carried out the research on the cost control of the multistage structure design of Si anode materials.The Si@C nano-structure was designed and synthesized by chemical method.The lithium storage performances are tested in half cells.In addition,we also study the enhanced capacity of constructing physical compartment of CuO nanowires.The contents and results of this study are mainly as follows.1.Copper oxide（CuO）nanowires arrays have been synthesized by thermal oxidation method,which is a simple preparation process without using a template or catalyst.By utilizing the advantages of both material and 1D architecture properties mentioned above,there is an opportunity to further enhance the performance of CuO for Lithium ion battery applications.The electrochemical performances of CuO nanowires were evaluated in half-cell configurations.The retention specific capacity is about 263 mAh g^-1 with high coulomb efficiency of 100%after 200cycles.And it was used to build constructing physical compartment for huge volume expansion of Si nanoparticles.Good electrochemical stability was achieved by this structure design.2.Carbon coated silicon nanoparticles（Si@C）were prepared via a facile approach,the carbon shells were conformally coated using the chemical bath deposition and subsequent carbonization of polydopamine as carbon source.When applied as a binder-free self-supported anode for lithium ion batteries,the Si@C electrode still deliver high reversible capacity of 836 mAh g^-1 at 100 mA g^-1after 200 cycles and 435 mAh g^-1 at high current density of 1600 mAg^-1.Accordingly,the composite nanoparticles displayed an enhanced electrochemical storage capacity and excellent rate performance.In addition,the Si@void@C structure was designed by choosing SiO₂ as sacrificial layer,but we have not get a desirable outcome for higher impedance of this structure.