Preparation And Electrochemical Performance Of Si-based Materials As Anode Material For Lithium-ion Battery

Silicon-based materials show great advantages as anode materials for the next generation of lithium-ion batteries,including abundant resources,environmentally friendly,low lithium insertion potential and high theoretical capacity,etc.However,resulting from large volume expansion,the capacity suffers a rapid decay during discharging and charging processes,which limits their commerical applications.To solve this problem,Si nanoparticles were employed due to its low absolute volume expansion rate,then mixed with graphite and amorphous carbon to construct silicon carbon composites.The graphite substrate not only enhances the conductivity of the composites but also alleviates the volume expansion of Si NPs.As a kind of soft medium,amorphous carbon coated on the surface of Si NPs prevents Si NPs from contacting with the eletrolyte,which directly helps to form stable SEI films during the charging and discharging process and alleviates the volume changes of Si NPs.In this paper,in order to improve the electrochemical cycle stability of the composites materials,two methods of high-temperature pyrolysis and chemical vapor deposition are used to prepare silicon carbon composites.The main content is as follow:1.The G/Si@C composites were synthesized via high-temperature pyrolysis.Their structure,composition and morphology were characterized by XRD,TG and SEM.The electrochemical properties of G/Si@C composites were tested by galvanostatic charging and discharging experiments.The morphology of Si,the content of Si,pyrolysis temperature and dispersion of Si NPs were investigated,respectively.Results showed that the G/Si@C composites synthesized under high-energy ball mixing,900 ? and with?10wt%Si exhibited the most excellent electrochemical cycling stability.The first charge capacity and 100th charge capacity were 450.7 and 428.3 mAh g-1 respectively at the current density of 100 mAh g-1.The capacity retention rate was 95.0%.2.The GSAC composites were synthesized via chemical vapor deposition.Their structure,composition and morphology were also characterized by XRD,TG,SEM,TEM and BET.The electrochemical properties of the GSAC composites were tested by galvanostatic charging and discharging experiments.The principle of this method and the influence of Si content and time of high-energy ball milling on the morphology and electrochemical properties of composites were investigated.The results showed that the GSAC composites prepared by this method exhibited much excellent electrochemical cycling stability.The first and 200th charge capacity of GSAC composites containing 10.5 wt%Si was 505.5 mAh g-1 and 468.6 mAh g-1 at the current density of 500 mA g-1,and the capacity retention rate was 92.7%.