Preparation And Performances Study Of Si/graphene Composite As Anode Materials For Lithium-ion Battery

With the rapid development of science and technology, the research of electric vehicles has become even more important. The key part of the electric vehicle is the battery, however, that it cann’t meet the application requirement when graphite used as anode materials. Silicon materials have attracted great attention for its high theoretical specific capacity, which is about 4200 m Ahg–1. However, low electrical conductivity and drastic volume change of silicon anode materials also limit its commercial application. In order to solve the problems and improve the cycle performance of silicon material, few-layers graphene sheet were prepared by liquid phase exfoliation method in this paper. High-power-tip-sonication method was used to fabricate silicon-graphene composite, which used the excellent properties of graphene, as a result, the cycling performance of silicon anode material can be improved.Scanning Electronic Microscopy, Raman Spectroscopy and Fourier Transform Infrared Spectroscopy were used to characterize the graphene which prepared by liquid phase exfoliation method. The results show that solvent is an important parameter. When the solvent is alcohol, the optimum surfactant concentration and ultrasonic time are 6 mg/m L and 10 h, respectively. When the ultrasonic solvent is the mixed solution of water and /N-methyl pyrrolidone and the volume ratio is 1:1, the optimum surfactant concentration and ultrasonic time are 4 mg/m L and 10 h respectively.Cycling stability and rate performance of electrode materials were improved by silicon-graphene composite which synthesized by high-power-tip-sonication method. According to the structure characterization and electrochemical measurement of graphene/silicon, in which graphene was prepared under optimal conditions when the solvent was ethanol, the result suggests that silicon nanoparticles were intercalated between graphene sheets and the favorite weight ratio of graphene and silicon in the composite was 2:3, and the mixing time was 3 hours. The discharge and charge capacities for the first cycle were 2561.2 m Ah/g and 1514.1 m Ah/g, respectively, corresponding to an efficiency of 60%. Compared with silicon materials, the irreversible capacity was obviously improved. After 100 cycles, the reversible capacity can be still as high as 1009.3 m Ah/g, and the average coulomb efficiency reach to 99.8%, which maintained about 66.7% of the capacity. The charge transfer resistance was about 33% of that silicon nanoparticles electrode after 3 cycles. When graphene was prepared using the distilled water/N-methyl pyrrolidone as solvent under optimal conditions, the results suggest that favorite weight ratio of graphene and silicon in the composite was 1:1, and the mixing time was 2 hours.The discharge and charge capacities for the first cycle were 2465.1 m Ah/g and 1439.7 m Ah/g, respectively, corresponding to an efficiency of 58.4%, and the charge transfer resistance was about 39% of that silicon nanoparticles electrode after 3 cycles. After 100 cycles, the reversible capacity can be still as high as 956 m Ah/g, and the average coulomb efficiency reach to 99.8%, about 66.4% of the capacity is maintained.