Preparation And The Electrochemical Performance Of Silicon/Carbon Composite Anode Materials For Lithium Ion Batteries

In recent years,Lithium-ion battery has been widely concerned due to the vital applications in automotive,electronics,energy storage devices and the emerging requirements of Lithium-ion battery as the power of automotive to reduces urban environmental pollution and haze.Lithium-ion battery can be used repeatedly,and has unique characteristics,such as high average working voltage,high energy density and environmental friendly makes Lithium-ion battery more prominent among all other available means.Yet energy density enhancement still lacks adequate development.The development of new anode materials paved the way for this purpose.Various materials have been studied,e.g.Silicon has great potential as anode materials because of the extremely high theoretical capacity(4200 mAh/g)and abundant source.However,huge volume change during the reaction in silicon made Lithium-ion battery causes the poor cycle ability.Silicon can be modified to overcome such complexity.One of the effective methods is to composite Si with carbon materials.In this work,micron structure silicon has been utilized as silicon source,three kinds of silicon/carbon composites(graphite/silicon,silicon/graphite/amorphous carbon and cladding type silicon/carbon)were synthesized by mechanical milling and pyrolysis method later compared with pure silicon powder electrode.Surface morphology,elemental composition and structure of the composites were analyzed by scanning electron microscopy(SEM),electron dispersion spectroscopy(EDS)and X-ray diffraction(XRD).The electrochemical performance was investigated by charge/discharge test,electrochemical impedance spectroscopy(EIS)and cyclic voltammetry(CV).First,electrochemical performance of the composites with the graphite as matrix was improved to different degrees compared with the pure silicon powder electrodes.The first discharge capacity of composites increased with the content of silicon,but high content results in ambiguity of stability.The composite material with the graphite/silicon wt%of 8:2 exhibits better electrochemical performance.Secondly,the cycle stability of the silicon/graphite/amorphous carbon composites synthesized having20wt%of silicon deescalated with the increase of the amorphous carbon content.Composites with silicon/graphite/amorphous carbon wt%of 2:7:1 showed better electrochemical performance e.g.Furthermore,cladding type silicon/carbon composites were prepared with sucrose as the basic material by pyrolysis method.Analysis revealed that the electrochemical properties of the composites corresponded to the carbon coating and the composite materials with the sucrose/silicon wt%of 70:30 exhibited relatively enhanced cladding and optimal electrochemical performance as well e.g.when the charge/discharge current density was 100 mA/g the first discharge capacity was up to 1400 mAh/g and sustains the value about 340 mAh/g after 50 cycles.