Structural Regulating And Lithuium Storage Properties Studies Of Nano Sillicon/Graphite Composite

At present, in order to prevent energy depletion and environmental pollution,various countries are scrambling to move into the new energy field. The lithium ion batteries are applied to provide energy for electric vehicles, but the current lithium ion battery is limited by its anode materials and cathode materials. Particularly, the current commercial graphite anode material has been unable to meet the application requirements. Silicon has attracted increasing attention as a potential high-capacity anode material because of high theoretical specific capacity of 4200 mAh/g, however, it suffers from some drawbacks involving the intrinsic low electrical conductivity and the drastic volume change during the alloying/de-alloying reactions with Li+, which restricts its application. In order to solve the problems and improve the cycle performance of silicon material, we produce silicon nanosilicon/spherical graphite composite by rotary chemical vapor deposition, the graphite can contribute its excellent conductivity and the nano silicon can contribute its high capacity, all of this can provide excellent electrochemical properties.Nanosilicon/spherical graphite is prepared by chemical vapor deposition method,the equipment is external heating rotary kiln, it has the effects of steady uniform deposition, nanosilicon particles is deposited on the surface of spherical graphite uniformly. For different CVD carrier gas and reactive atmosphere, we obtained that N₂ as the carrier and the reactive atmosphere can make the structure of composite to be better than the composite that is prepared in other reactive atmosphere. When the ratio of TCS and carrier gas is 2:8, the size of silicon got within 100 nm in the composite, and they are uniform and stability, and distributed uniformly on the spherical graphite, the discharge and charge capacities for the first cycle are 450.1 mAh/g and 488.4 m Ah/g respectively, corresponding to an efficiency of 92.1%. After 30 cycles, capacity remains at 440.8 mAh/g, capacity retention rate is 97.9%. Ulteriorly, the CVD reactive time is optimized. When the reactive increases, the utilization of TCS decreases because the gas of TCS can not reactive completely. When the reactive time is 40 min, the structure and morphology of composite exhibits excellent feature, and it also shows superior electrochemical properties. Moreover, the reactive temperature is optimized, when the composite is deposited at low temperature, due to the incomplete decomposition of TCS,the utilization of TCS and the content of silicon is lower. When the reactive temperature is high, although the content of silicon is exceeding, the size of Si can reach 200 nm,and are connected together. Only the reactive temperature is 700 ℃, composite shows excellent performance.Coated the prepared materials nanosilicon/spherical graphite can optimize the properties of composite, the coated parameters are studied. When the content of pitch that is used for coating is 10 wt%, the pitch and nanosilicon/spherical graphite is coated at 700 ℃,and the coated time reaches 4 h, the samples can possess superior properties.