Research On Synthesis And Electrochemical Performance Of Silicon-based Anode Materials For Lithium-Ion Batteries

Silicon(Si)is considered to be one of the most promising anode materials in lithium-ion batteries due to its ultra-high theoretical specific capacity(?4200 mAh g-1)and low working potential(?0.5 V).However,silicon not only has poor electronic conductivity,but also its huge volume change during the charging and discharging process results in the pulverization of silicon particles,along with continuous formation of unstable SEI film,leading to rapid decreasing of the electrochemical performance.Therefore,in this paper,various silicon-based composite materials were synthesized to improve the electrochemical performance of silicon,such as silicon@nitrogen-doped carbon(Si@N-C),silicon/nitrogen-doped carbon@silica(Si/N-C@SiO₂),silicon/nitrogen-doped carbon@titanium dioxide(Si/N-C@TiO₂)and so on.The structure of the composite material is analyzed by characterization methods,and the electrochemical performance of the electrode material is explored by electrochemical test methodsFirst,the silicon@polyaniline(Si@PANI)precursor was prepared by using silicon,aniline,ethanol,deionized water,and ammonium persulfate as raw materials under ice water bath conditions,and then a series of products Si@N-C could be obtained by pyrolysis under nitrogen atmosphere.We explore the effect of different ratios of silicon and aniline on electrochemical performance of materials.The results show that the capacity retention of the Si electrode after cycling 100 times at a current density of 200 mA g^-1 is only 5.04%.In contrast,the electrochemical performance of all Si@N-C electrodes have been significantly improved,which is attributed to the introduction of the N-C shell to improve the structural stability of the composite materials.Among them,when the synthesis condition is that the mass ratio of silicon to aniline is 40%,the cycle performance and rate performance of the Si@N-C-2composite material are the best,and the mass fraction of nitrogen-doped carbon in the composite material can be calculated by the TGA results is 45.3wt%.The initial discharge specific capacity of the Si@N-C-2 electrode is 1769.8 mAh g^-1 at the current density of 200 mA g^-1.And the specific discharge capacity is still as high as989.9 mAh g^-1 after 100 cycles.Secondly,the Si/N-C@SiO₂ composite material was synthesized by chemical oxidation polymerization method,sol-gel method and high temperature pyrolysis method.The results show that N-C and SiO₂ play a synergistic effect,and the Si/N-C@SiO₂ electrode has better cycle performance and rate performance.The initial discharge specific capacity of Si/N-C@SiO₂ electrode is 1517.2 mAh g^-1 at the current density of 200 mA g^-1.After 100 cycles,the discharge specific capacity is731.8 mAh g^-1.Finally,silicon/polyaniline@titanium dioxide(Si/PANI@TiO₂)precursor was synthesized by chemical oxidation polymerization and sol-gel method,followed by heat treatment under nitrogen atmosphere at different temperatures to obtain Si/N-C@TiO₂ composites with different crystal forms.The research shows that the TiO₂ of Si/N-C@TiO₂-750 synthesized by calcination at 750^oC of the precursor mainly exists in the form of anatase and rutile mixed crystals.Overall,the cycle performance and rate performance of Si/N-C@TiO₂-750 electrode are the most excellent.The initial discharge specific capacity is 1201.9 mAh g^-1 at the current density of 200 mA g^-1.After 100 cycles,the specific discharge capacity is 812.8 mAh g^-1 with a capacity retention of 67.63%.Even at a large current density of 2 A g^-1,the average discharge specific capacity is still 739.32 mAh g^-1.