| Silicon not only is the main ingredients of solar cells, but also has become new anode materials for lithium-ion battery. In the solar cell production process it will bring silicon waste mostly are discarded. Main component of the waste is silicon powder and silicon carbide. If there are some methods to extract silicon from solar cell and are use them in lithium-ion battery, not only solves the problems of source of silicon powder and turn waste for treasure, made great contribution to the environmental protection. This paper adopted three methods:phosphate removing silicon carbide, high temperature removing silicon carbide and physical separation to deal with silicon scrap, trying to extract high purity silicon powder. XRD calculation showed the former two methods couldn't separate silicon and silicon carbide effectively. The physical separation method which using the density difference(silicon 2.32-2.34g/cm3, silicon carbide 3.20-3.25g/cm3). choose three methyl bromide (density 2.847 g/cm3) as solvent in the mixture. It obtained upper and lower material through centrifugal separation. Analysis by XRD, this method could separate silicon and silicon carbide under normal temperature. will separation of silicon and silicon carbide, In dry waste, extraction rate of silicon can reach 90%+ and silicon carbide can be extracted thoroughly, so both of them can be recycled. Silicon carbide can be used as abrasive again, and silicon as raw material of anode materials for lithium-ion battery.But pure silicon anode materials have as serious volume effect in the process of Li+ intercalation, and directly led materials particles to rupture and lose the electrochemically active. This paper adopt the method of electroless copper plating to prepare silicon copper composite powder, using the REDOX reaction in plating solution to deposit a layer of copper on silicon surface. Make full use of copper conductivity to increase the electrical conductivity of electrode, and through the ductility of copper to relieve volume effect of silicon, curb its particles rupture and pulverization, thereby improving cycle properties of the battery.Strict pretreatment before plating is required because silicon powder is the nonmetallic material, and powder has high spicific surface area, the concavo-convex surface characteristics. First is silicon powder cleaning and surface coarsening. Observed by SEM:5% NaOH coarsening solution could make surface rough. Second is the activation of silicon powder which using colloidal palladium, this method fundamentally solve the replacement between palladium and copper ion. Exploration experiment indicated the concentration ratio of Sn2+ and Pd2+ is 2, temperature in 45℃, reaction time 2h. Through single factor analysis and orthogonal analysis in electroless copper plating, get a optimal ratio of plating solution: 0.05 mol/L Cu5SO4-5H2O(main salt),0.078 mol/L Na3C6H5O7·2H2O(complexmg agent),0.3625 mol/L NaH2PO3·H2O (reductant),0.7915mol/L H3BO3(stabilizer),0.2mg/L thiourea (stabilizer), 0.01/L NiSO4-7H2O(accelerant),temperature is 65℃and pH value is 9-10.Phase analysis by X-ray diffraction (XRD), morphology was observed by scanning electron microscopy (SEM) and (TEM), performance of electrochemistry was examined by charging and discharging test. The result shows:Silicon surface are coated with a layer of dense copper particles. The compsite showed (111) and (200) copper crystal face diffraction peak at 43.355°and 50.482°respectively. The Si/Cu composites anode of lithium-ion batteries show well electrochemical performance:the initial discharge specific capacity reached 1185mAh/g. After 30 cycles, the capacity gradually reduced to 350mAh/g and could maintain 350mAh/g in the next 30 cycles. Therefore, Si/Cu composite can inhibit the volume effect of Si and improve the cycle performance of the electrode. Provide a new thought for high capacity and stable anode materials for lithium-ion battery. |
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