Si/C Nanocomposites Anodes:Synthesis And Application For Lithium-Ion Batteries

Morden society face a great challenge in meeting the increasing demand of novel lithium-ion battery?LIB?with high energy densities and long cycle life due to the development of portable electronic devices and electric vehicle in daily life.Si has been considered as the most promising anode materials for LIB because of it's high gravimetric and volumetric capacities compared to commercial graphite anodes.However,Si electrode experiences a tremendous volume change during Li insertion and extraction processes,which induces severe pulverization of the active materials and subsequent rapid capacity fading.Hence many great efforts have been made to address this problem.In this dissertation,various of silicon-carbon nanocomposites with different structures and components are designed and synthesized via various synthetic methods.Specifically,we have prepared MWCNTs@Si nanocomposites,MWCNTs@Si/SiO_x@C nanocomposites,RGO@Si nanocomposites,porous Si@C nanotubes,Si/SiO_x porous structures,superfine Si/C porous structures,porous Si/C nanocompositesderivedfrom CO₂ inorganic carbon sources.Some synthetic methodssuch as TEOS hydrolysis SiO₂ coating,magnesiothermic reduction,chemical vapor deposition,seed-assisted hydrothermal method,spray drying process have been applied.the above-mentioned Si/C nanocomposites anodes exhibit improved electrochemical performance due to the advantages of the novel structural properties.The main innovative results are listed as follows:?1?Uniform MWCNTs@Si andMWCNTs@Si/SiO_x@C nanocomposites are successfully synthesized via the magnesiothermic reduction of pre-synthesized MWCNT@SiO₂ nanocables.When used as anode materials for lithium-ion batteries,the as-synthesized MWCNT@Si nanocomposites show better electrochemical performance than the bare Si nanoparticles and MWCNTs.Moreover,the MWCNTs@Si/SiO_x@C nanocomposites exhibit enhanced cycling life compared to MWCNT@Si,which can be attributed to the novel core-shell porous structure as well as the enhanced electronic conductivity and lithium-ion transport.?2?Firmly bonded reduced graphene oxide?RGO?@Si nanocomposites are successfully synthesized via in-situ magnesiothermic reduction of pre-synthesized GO@SiO₂ composites.When used as anode materials for lithium-ion batteries,the as-synthesized RGO@Si nanocomposites show high reversible capacity,excellent cycling performance and good rate capability,which attributed to the novel uniform nanostructure and the volume expansion tolerance,the strong binding force between Si nanoparticles and graphene sheets.?3?Porous Si@C coaxial nanotubes are prepared by layer-by-layer assembly on ZnO nanorod templates and subsequent magnesiothermic reaction.The ZnO nanorods synthesized by a seed-assisted method can act as the template to deposit a compact SiO₂ layer.Due to the coaxial nanotubular porous structures and carbon layer,the porous Si@C coaxial nanotubes demonstrate excellent cycling stability and high specific capacity as anode materials for lithium-ion batteries.Furthermore,it shows better cycling stability when worked in the VC-containing electrolyte system.?4?A novel Si/SiO_x porous structure is prepared via controllable annealing and subsequent acid washing of Mg2Si.When used as anode materials,the Si/SiO_x porous structure with?9 nm SiO_x coating layer demonstrates high reversible discharge capacity of?915 mAh g-1 after 500 cycles at 1 A g-1.The lithiation mechanism of different thickness of SiO_x layer has also been investigated.Superfine porous Si/C structures with different particle size are prepared,which shows the pro-longed cycle life?1000 cycles at 1 A g-1?and a broad commercial application prospect.Porous Si/C nanocomposites derived from CO₂ have been characterized in detail by various methods,which exhibits relativehigh specific capacity and good rate performance.