Preparation And Electrochemical Performance Research Of Silicon-based Anode Materials For Lithium-ion Batteries

Lithium-ion batteries have been world widely investigated and used in hybrid electric vehicles（HEV）,pure electric vehicles（PEV）and portable devices,because they have high energy density,long lifespan,and no memory effect.Compared to the conventional graphite anode,silicon has many advantages,such as its high theoretical capacity(4200 mAh g^-1),low working potential,abundant and environmentally benign nature.However,practical application of Si anode materials is seriously hampered by its poor intrinsic conductivity and the huge volume variation（over 300%）during repeated lithiation / delithiation process,which lead to severe pulverization,cracking,and then a rapid capacity fading.In this paper,we developed a series of synthetic route to fabricate high-performance Si-based anode materials.SEM,TEM,EDX,XRD,TGA and laser particle size analysis were used to characterize the morphology,structure and composition.CV,galvanostatic charge-discharge and EIS were used to systemically analyze the electrochemical performance of these materials.（1）The composite material of Si sub-micrometer wires with the nickel and carbon modifications were obtained via a convenient solution etching approach and a simple pyrolytic reduction process.In combination with the uniform dispersion of nickel nanoparticles and the coating of carbon,the as synthesized composite electrode demonstrated good cycling stability and rate capability,delivering a high reversible capacity of 900 mAh g-1at 1C.（2）Preparation of Si@Ag@void@C was realized through etching the Si@SiO₂@C precursor with AgNO₃ and HF aqueous solution,and followed by adding citrate to optimize the effect of silver nanoparticles which modified on silicon yolk.Because of the dispersion of silver nanoparticles,the electrical contact between siliconyolk and carbon shell was improved.Si@Ag@void@C demonstrated good rate capability,delivering a high reversible capacity of 600 mAh g^-1 at 2 A g^-1.（3）A novel method to synthesize the Si@SiO₂ micrometer-sized secondary clusters with a solvothermal approach was designed.In the solvothermal approach,transition metal silicate are grown in situ around the surface of the Si@SiO₂ nanoparticles.After Si@SiO₂ micrometer-sized secondary clusters was obtained,carbon coating and hydrofluoric acid etching was further exerted to synthesize the nanostructured Si secondary clusters（Si SCs）,which demonstrated good cycling stability and rate capability.The good electrochemical performance of Si SCs anode can be attributed to the optimized structural designs（novel nanoscale architecture）.Firstly,the carbon framework provided fast channels for electron transfer.Secondly,the well-defined built-in void space allows Si nanoparticles to expand and contract during the insertion and extraction of lithium ions without deforming the Si SCs electrode microstructure.Thirdly,Si nanoparticles had been restricted within the carbon framework during the cycling.