Study On Preparation And Electrochemical Properties Of Porous Silicon/Carbon Composite Anode Materials

Silicon has become the most promising anode material for the power Li-ion battery because of its high theoretical specific capacity and low discharge potential.However,the poor conductivity of silicon and its huge volume change in the process of charging and discharging,which lead to the silicon particles crazing,peeling and even losing contact with the current collector..Meanwhile,silicon easily losses contace with the conductive agent around when it shrinks after leaving of Li+,which is an important reason of low coulombic efficiency and poor cycling life.These problems seriously restrict the industrial process of silicon anode material.In this paper,the micron porous silicon@carbon anode materials with controllable specific capacity were prepared,and the carbon materials and polymer materials with good conductivity were introduced.The main research contents are as follows:Porous silicon samples were prepared by etching commercially available Al-Si alloys powder,Al₆₀Si₄₀,in acid condition,and PSi@C composite material was prepared by thermal decomposition of porous silicon mixed with starch.the capacity retention rate of PSi@C-8.8 material with 38wt%silicon can reach 95.4%after 200 cycles at the current density of 0.4 A/g.When the current density is 2 A/g its reversible capacity is 352 mAh/g.In this work,the effects of raw material ratio,acid treatment temperature and carbonation temperature on the electrochemical properties of PSi@C composites were studied.The results show that the volume expansion rate of porous silicon covered with carbon shell was effectively reduced,and the electrochemical cycling stability and multiplier performance was improved,and the cyclic stability of composites decreases with the increase of acid treatment temperature.With the increase of carbonization temperature,the cyclic stability of composites increases.To improve cyclic performance of the PSi@C composites with high specific capacity in the above studies,a kind of pomegranate porous silicon@carbon/reduced graphene oxide?PSi@C/RGO?composite material was prepared through ultrasonic dispersion and freeze-drying by introducing graphene for secondary compounding.Silicon is the main source of capacity,the coated carbon layer and the graphene reduce the electrochemical impedance of PSi@C/RGO,and the space reserved in the structural design can effectively alleviate the volume expansion rate of silicon,so that the composite shows good electrochemical cycling stability.At the current density of 0.4 A/g,the reversible capacity was 824 mAh/g for 200 cycles,and the capacity retention rate was 81.2%.In order to obtain the good cyclic stability of PSi@C composites,PSi@C@PANI composites were prepared by coating a layer of polyaniline?PANI?.The double core shell structure of PSi@C@PANI particles connected with chemical bond can bear a large cubic expansion without being destroyed by the stress.The composite with the mass percentage of amorphous carbon is30.4%and the mass percentage of PANI is 10.5%,expanded the best cycle performance.,under the current density of 0.5 A/g,the reversible specific capacity of the composite material is 1005mAh/g,and the capacity retention rate is 66.6%after 100 cycles,which is higher than the capacity retention rate of PSi@C without polyaniline coating?54.8%?.