Investigations On Preparation And Characterization Of Silicon-graphite Composite Anode Materials

Stable graphite is a mature anode material for lithium-ion batteries,while highcapacity silicon is considered as a promising anode material for the next generation of lithium-ion batteries.In this paper,nano silicon and artificial graphite as the main raw materials,the preparation of silicon-graphite composite anode material,explore the combination of silicon and graphite,the effect of adding adhesives and surface modifiers on material properties.On this basis,the effect of graphite size on the properties of the composites was studied,and the composites were coated twice,and the products with high gram capacity and long cycle life were prepared to meet the requirements of commercial production.The specific research contents are as follows:1.According to a certain proportion of mixed silicon and graphite,by adding adhesive and surface modification,silicon and graphite are combined,compared the performance of the material to determine the best composite way.The experimental results show that adding asphalt as a binder can better retain the silicon particles attached to the graphite surface,making the specific capacity of the composite material high,and with the increase of the asphalt proportion,the material’s cycle performance is improved,but the capacity and the first effect will be reduced.This experiment determined that 10% asphalt added ratio is the best ratio,while the proportion of modifier should not be too high.The addition ratio of 0.5% is optimal.Using a combination of several ways to make the best performance of the Silica-graphite composite material for the specific capacity of 990 m Ah/g,the first effect of 91.7%,button battery cycle 100 laps capacity retention rate of 73.7%.2.The effect of graphite size on silica-graphite composite anode material was studied,and it was found that the anode material made of small-size graphite had better electrochemical performance,and the capacity retention rate decreased to 80% after716 cycles.This is because the smaller graphite has a better encapsulation form when it is combined with nano-silicon to form the silicon-graphite particle material,which can maintain the continuity of electron and ion transport without forming large gaps in the electrode during the volume expansion of Si.3.The secondary coating effects of different carbon sources were studied,and it was found that the anode material prepared with phenolic resin as the secondary coating carbon source had better performance.The electrochemical performance of cylindrical batteries was characterized by using phenolic resin as the secondary coating carbon source.However,the composite without secondary cladding lasted only 651 cycles.By further exploring the high and low temperature properties,it is found that when the silica-graphite composite material is coated with resin as carbon source,the structure formed is more stable and the high and low temperature properties are more superior.Compared with normal temperature,the retention rate can reach 85.6% at-20℃.Stored at 60℃ for 7 days,the capacity retention rate is 95.6%,showing excellent stability.