Preparation And Properties Of Silicon-carbon Composite Anode Materials For Lithium Ion Batteries

Lithium-ion battery has become a favorite in the field of new energy development because of its excellent performance.The characteristics of large capacity and high rate is the most important research direction of the battery at present.Silicon has a higher specific capacity of(4200 mAh/g)and a lower voltage platform(0.01~0.2 V),but its direct negative electrode has a natural defect.When lithium is embedded out of the unit cell of silicon,the volume of silicon material will change seriously and the capacity will decline rapidly.A large number of studies have found that the combination of silicon and other materials can effectively alleviate the volume effect of silicon and increase its cycle life,and the silicon-carbon composite is the most promising composite.At present,artificial graphite is the main anode material for commercial lithium ion batteries.However the preparation of artificial graphite needs high temperature calcination,high production cost and high price.It is a research focus to find new low-cost biomass carbon materials to replace artificial graphite.In this paper,three kinds of biomass carbon materials,pine,peach and peanut hulls,were studied,and then collocated with nano silicon powder,phenolic resin was used for in situ coating and electrostatic spinning.Silicon-carbon composite anode materials for lithium ion batteries were prepared.The results of the study were as follows:(1)By comparison,it was found that pine was a relatively ideal carbon material to replace artificial graphite.(2)Silicon-Biomass-carbon-Phenolic Resin Composites prepared by inverse emulsion system of phenolic resin in situ.The silicon-pine sawdust phenolic resin composite had excellent electrochemical properties.At 38.5 mA/g current density,the first coulomb efficiency was 60.17%.After nearly 40 cycles,the discharge specific capacity was as high as 390 mAh/g.Experimental results showed that by adding carbon materials to silicon-phenolic resin composites,carbon materials played a role of dispersion and isolation,so that the particles of nano-silicon-phenolic resin composites can be dispersed and their relative volume reduced.Thus,the infiltrating ability of electrolyte in the composite was enhanced,and the intercalation and release of lithium ions in the composite were favorable,and the electrochemical properties of the composite were improved.(3)Silicon-carbon-polyacrylonitrile carbon fiber composites were prepared by electrostatic spinning.The silicon-polyacrylonitrile carbon fiber composites had excellent electrochemical properties.At 30 mA/g current density,the first discharge specific capacity of the composite was 991.7 mAh/g,the first coulomb efficiency was 70.96%.After nearly 30 cycles,the discharge specific capacity was still up to 730.1 mAh/g.However,the addition of biomass carbon materials can not improve the electrochemical performance of silicon-polyacrylonitrile carbon fiber composites.On the contrary,because of the larger particle size of carbon materials,the complete continuous structure of the fibers was destroyed.Therefore,adding biomass carbon directly to the spinning solution of silicon-polyacrylonitrile did not improve its performance obviously.