Preparation And Electrochemical Properties Of Si/C As Anode Materials For Lithium Ion Batteries

Silicon materials have the highest theoretical specific capacity(4200m Ah·g^-1)among the anode materials studied at present,but the extremely low intrinsic conductivity and serious volume change during charging and discharging lead to extremely poor rate and cycle performance.Therefore,improving the conductivity of silicon materials and alleviating the physical changes in the process of charging and discharging are the main research directions of silicon materials.In this paper,porous silicon was prepared from commercial Si/Al alloy by acid etching;Si/C composites were prepared with aniline and starch as carbon sources to improve the electrical conductivity and structural stability of silicon-based materials;The composition and morphology of the materials were characterized by physical characterization,and their electrochemical properties were tested.The relationship between the electrochemical properties and microstructure was analyzed.The main research contents are as follows:(1)Preparation of Si/C composites with aniline as carbon source:the effects of preparation methods,different Si/Al alloys and coated carbon content on the structure and electrochemical properties of Si/C composites were studied.The results show that:Using Si/Al(m _Si=20wt.%)alloy as raw material,silver deposition is carried out in 0.04M Ag NO3+0.1%HF solution,and the mass ratio of Si/S and Si/aniline is 1:3 and 1:2respectively Pani@20%Si/Ag The results show that the composite has the best electrochemical performance,and the first discharge capacity of the composite is2714m Ah·g^-1 at 0.1A·g^-1,For the first time,the coulomb efficiency is 77.89%,and the reversible specific capacity of 786m Ah·g^-1 is obtained at high current density.The reversible specific capacity of 770m Ah·g^-1 was obtained after 100 cycles at 1A·g^-1.(2)Si/C composites were prepared with starch as carbon source,porous silicon was prepared with commercial Si/Al alloy,and starch as carbon source.The results show that Ni doping can not only form Ni₂Si on the surface of Si to improve the conductivity of the material,but also change the properties of starch based carbon to form carbon nanotubes to improve the conductivity and structural stability of the material;CNTs are intercalated in starch based carbon to form a conductive network,which further improves its conductivity.When the doping amount of Ni is 0.5mmol/g·C and the doping amount of CNTs is 10mg,the ST/Ni@20%Si/CNTs-10 composite has the best electrochemical performance,the first discharge specific capacity is 1819m Ah·g^-1 at 0.1A·g^-1,the reversible specific capacity is 819m Ah·g^-1 at 3A·g^-1,and the reversible specific capacity is 516m Ah·g^-1 after 200 cycles at 0.5A·g^-1.