Preparation And Performance Study Of Silicon-based Negative Electrode Materials For Lithium-ion Batterie

Silicon has advantages such as high specific capacity（4200 m Ah/g）,low lithium embedding potential,and abundant reserves,which is considered to be the most suitable materials to replace graphite anode.But the commercial silicon particle size is too large to be used directly as the electrode material,and the silicon material will have a huge volume expansion in the process of lithium insertion,causing the active material to fracture and fall off the collector,which ultimately leads to a rapid decrease in battery capacity.The defects seriously affect the commercial application of Si-based anode materials.In this paper,the Si-based anode material was modified for defects,the main contents are as follows:（1）Using commercial silicon as raw material,silicon particles were refined through high-energy ball milling,and the effect of different ball milling parameters on the particle size of silicon powder was studied.At the same time,the influence of silicon powder particle size on electrochemical performance was also studied.The results showed that silicon powder with small particle size has better cycling performance.The optimum process parameters of dry ball milling are as follows:grinding time 60 min,grinding speed 1200/1300 rpm.The silicon powder prepared under this process has the smallest particle size(D₅₀ is 0.8μm).The reversible specific capacity of this material is 1791.7 m Ah/g at a current density of 4000 m A/g,and the capacity retention rate relative to the fourth cycle is 20.5%after 100 cycles This result showsed that simple refinement of silicon particles has a smaller effect on alleviating volume expansion.（2）In order to provide more space to alleviate the volume expansion of silicon,porous silicon materials were prepared by chemical etching method.The aluminum matrix in the alloy was removed by hydrochloric acid etching and then porous silicon was obtained.The Al-Si alloy prepared by atomization method exhibits a three-dimensional porous spherical structure after etching,and the abundant pores reserved space for volume expansion during the lithium intercalation process in silicon and improved the lithium ion transport rate.The reversible specific capacity of this material is 1269 m Ah/g at a current density of 4000 m A/g,and the capacity retention rate relative to the fourth cycle is 59.5%after 100 cycles.Compared to ball milled silicon,the capacity retention rate has increased by 25.7%.（3）The silicon material was coated with dopamine.Firstly,the effect of dopamine content on the coating effect and electrochemical performance of silicon materials was studied.The results showed that the coating is most useful and the electrochemical performance is best when the dopamine content is 20 wt.%.The electrochemical performance of dopamine-coated silicon,dopamine-coated porous silicon and dopamine-coated porous silicon carbonization were compared when the content of dopamine was 20 wt.%.The results showed that dopamine coated porous silicon materials exhibit excellent cycling performance.The reversible specific capacity of this material is 1230.2 m Ah/g at a current density of 4000 m A/g,and the capacity retention rate relative to the fourth cycle is 73.3%after 100 cycles.Compared to uncoated porous silicon,the capacity retention rate has increased by 13.8%.In summary,silicon particles were refined and porous silicon and dopamine-coated silicon materials were prepared.The problem of volume expansion during charging and discharging of Si-based materials was improved,and the electrochemical performance of Si-based materials was improved.