| In order to obtain better performance in the fields of electronics and energy storage,exploring and developing lithium-ion batteries with high safety?high energy density and environmental friendliness has become one of the goals pursued by researchers.The energy density of lithium-ion batteries depends on the capacity and performance of the anode material itself.The abundant silicon material on the surface has a theoretical specific capacity of up to 4200 mAh?g-1,which is the new anode material with the most potential application.However,the poor conductivity and severe volume expansion of silicon during the intercalation/lithium charging process lead to rapid attenuation of the capacity,which greatly limits the charge and discharge cycle performance.At present,researchers love to change this state through the effective compounding of silicon and carbon materials.In this paper,nano-silicon/graphene?Si@G?composite anode materials were prepared by high-energy ball milling.The structure and morphology of the materials were analyzed by XRD and SEM,and their electrochemical properties were studied.Compared with the pure silicon electrodes,the electrochemical properties of silicon/graphene composites with different high-energy ball milling times have different degrees of lift off.The Si@G composite with high-energy ball milling for 20 min delivers the highest initial discharge specific capacity(3418 mAh?g-1)and the first coulombic efficiency?89%?,but its charge and discharge cycle stability is poor,and the discharge specific capacity is only 538.8 mA·h/g after 100 charge-discharge cycles.After charging and discharging for 100 times,the capacity of the Si@G composite material with high-energy ball milling for 20 min remained at 74.69%of the initial discharge specific capacity.X-ray diffraction analysis shows that a small amount of electrochemically inert silicon carbide?SiC?appeared in the composites.The impurity phase SiC without lithium storage capacity causes the first charge-discharge ratio of Si@G composite material to decrease,but it is beneficial to improve the stability of charge and discharge cycles.Secondly,on the basis of Si@G composite material with high-energy ball milling for 40 min,sucrose and emulsified asphalt were added for secondary ordinary ball milling,at the same time,the silicon/graphene/amorphous carbon?Si@G/C?composite was prepared after high temperature carbonization.The Si@G/C composite containing sucrose showed the highest initial discharge specific capacity and the first coulombic efficiency,which were 2500.1 mAh?g-1 and 85.67%,respectively.After charging and discharging for 100 times,it was found that the specific discharge capacity was as high as 1983.2 mAh?g-1,which was 79.33%of the initial discharge specific capacity.This indicates that the amorphous carbon after pyrolysis of sucrose adheres to the nano-silicon particles,which effectively inhibits the aggregation of silicon particles and exhibits relatively better electrochemical performance.Thirdly,in order to reduce the cost of raw materials and improving the universality of preparation methods,we reduce the specific gravity of silicon and graphene,and use graphite as a new carbon source,The silicon/graphene/graphite/petroleum asphalt?Si/G/C?composite material is passed through a total of three ball milling:the Si@G composite with ball milling for 40 min was used as the silicon source,and graphite and petroleum asphalt were sequentially added for ordinary ball milling and then subjected to high-temperature carbonization.Electrochemical studies have shown that the petroleum asphalt mass ratio of 3%Si/G/C composite exhibits better electrochemical performance.The first discharge specific capacity is about 743.1 mAh?g-1 at a current density of 100mA?g-1.When the cycle is 100 times,the specific discharge capacity can be maintained at about 537.4 mAh?g-1. |
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