Preparation And Modification Of Silicon-Graphite-Carbon Composite Anode Materials

Silicon/graphite composite anode materials have been widely studied as the most promising new generation anode materials for lithium-ion batteries with high energy density and long cycle life.However,the simple combination of silicon and graphite can easily exposes silicon to the electrolyte and causes many side effects.In addition,nano-silicon is difficult to be uniformly and stably dispersed on graphite,and it is easy to agglomerate together to cause electrochemical "sintering" phenomenon.For this reason,pitch is often used as the carbon source for the outermost carbon coating.In this paper,commercial artificial graphite and nano-silicon are used as raw materials,pitch is used as the carbon source,and different composite mixing methods are used to make the nano-silicon more uniformly dispersed in the artificial graphite and coated by the carbon source after the pitch cracking.Si/G/C(silicon/graphite/carbon)composite anode material with high gram capacity,long cycle life,and commercial production is prepared.At the same time,on this basis,the surface morphology of the material is modified by doping different proportions of carbon nanotube materials and spray drying methods to prepare commercial silicon-carbon material products.The specific content is as follows:(1)The effect of different mixing methods on material properties was studied through three different combinations(ball mill + high-efficiency mixing modifier(VCH),drum machine + VCH,high-efficiency tapping fusion coating machine(VSH)+ VCH).The silicon-graphite-carbon composite material was prepared by mixing method and the product performance was tested.It was finally confirmed that VSH +VCH was the optimal mixing method,and the Si/G/C composite material prepared by this method had the most excellent performance.The initial charge specific capacity is432.6 m Ah/g,and the capacity retention rate is 97.46% after 50 cycles.(2)The effect of different ratios of carbon nanotube doping on the properties of Si/G/C composites was studied,and the composite materials with different ratios of carbon nanotube doping at 0.5%,1.0%,and 1.5% were prepared,And we used it as the negative electrode material to prepare a soft-packed full battery to test its performance.As the proportion of carbon nanotubes increases,the cycle stability of the material first increases and then decreases.The composite material prepared with 0.5% CNT material has the best electrical properties,and its initial charge/discharge capacity is1661.9/1403.2 m Ah,respectively.The initial coulombic efficiency is 84.43%.The discharge capacity after 300 cycles at 1 C(1C=1400 m Ah)current density is 1067.7m Ah,and the capacity retention rate is 76.09%.(3)The effect of spray drying methods on the morphology and properties of the material was studied.The porous spherical modified silicon was prepared by spray drying.Its first charging specific capacity is as high as 2061.5 m Ah/g,the initial coulombic efficiency is 88.42%,and the cycle is 50 cycles.The post-capacity retention rate is 72.95%,and the downward tends to stabilize.Then it was mixed with artificial graphite,pitch,and carbon nanotubes to prepare Si/G/C composite material,and used as the negative electrode material to prepare a soft-packed full battery and test its performance.The initial charge/discharge capacity is 1747.4 /1418.8 m Ah,the initial coulombic efficiency is 81.20%,and it is still 1107 m Ah after 300 cycles at 1 C current density,and the capacity retention rate is 78.02%.The cycle stability of the material is greatly improved compared with the unmodified material.