Preparation And Electrochemical Properties Of Porous Silicon/Carbon Composite As Anode Materials For Lithium Ion Batteries

Due to the increasing demand for batteries with high specific capacity,silicon-based anode materials have been attracted the attentions of researchers;they are considered to have the potential to replace the commercial graphite anode materials.However,the silicon-based anode materials have some disadvantages,such as,poor conductivity and a large volume expansion accompanying charge-discharge process,which limiting their commercial application.Now,many countermeasures have been adopted to improve the performance of silicon anode materials.The coating of carbon layer on the surface of porous silicon has become one of the hot spots of the study of silicon anode materials,and it is also the main research content of this paper.The pore structure in silicon particles can not only reduce the diffusion resistance of lithium ions,but also alleviate the mechanical stress generated by volume expansion of silicon particles during charge-discharge process.Therefore,in the first part of this paper,20 wt%silicon-aluminum alloys is used as raw material to prepare porous silicon/polyaniline-based carbon composites by acid etching,sulfur melting,polyaniline coating and carbonization at high temperature.The effects of the step of sulfur melting during preparation on the structure and electrochemical properties of the as-prepared composites were investigated,and the effects of carbon content on the electrochemical properties of the composites were further explored.The results show that the composites with the best electrochemical performances are prepared under the following conditions:the mass ratio of aniline to porous silicon is 2:1,the sulfur melting process is concluded,and the heating rate of carbonization is 1°C·min^-1.The first coulombic efficiency of composites prepared is as high as 78%,and the capacity is as high as 751 mAh·g^-1 at 1 A·g^-1,and maintained at 700 mAh·g^-1 after 100 cycles at 0.5A·g^-1.The capacity retention is 79%.The physical and electrochemical properties of porous silicon/carbon composites prepared using asphalt as carbon source were also investigated.Firstly,the silicon-aluminum alloy was immersed in the chloroform solution of the asphalt,and then the porous silicon/asphalt-based carbon composite material was prepared by drying,pickling and high-temperature carbonization.The structure and electrochemical properties of the composites were studied.The results show that when the mass ratio of asphalt to silicon-aluminum alloy is 0.05,the first coulomb of the composites is 82%,and the capacity is still as high as 992 mAh·g^-1 at 1 A·g^-1.Moreover,the capacities are maintained at 856 mAh·g^-1 and the capacity retention rates is 51%after 100 cycles at0.5 A·g^-1.