Preparation And Electrochemical Properties Of Nano-Porous Silicon And Composite Meterials

With a theoretical specific capacity as high as 4200 mAh/g, low charge/discharge potential and abundant reserves, silicon has been considered as the most promising anode materials for the next generation high-performance lithium-ion batteries. However, the silicon anode easily suffers from a large volume expansion/shrinkage ?-300%? during cycling process, which causes electrode pulverization and lead to the reduction of capacity rapidly, limiting the commercial application.While the porous silicon is an attractive material choice to enhance the reversible capacity and rate properties because of the specific porous structure can be better able to accommodate volume changes and shorten the Li+diffusion path length.In this work, the nanoporous silicon was prepared from natural nanoporous silica obtained from a cheap rice husks. Compared with the traditional process, this method has the advantages of higher purity, cheaper prices and simpler technology. In order to obtain an optimal method and the good electrochemical performance of nanoporous silicon, the effects of the mechanism of the pyrolysis of rice husks and magnesiothermic reduction on microstructures and properties were discussed in detail. Meanwhile, to enhance Coulombic efficiency of the first cycle and the excellent cycle stability, the silicon/silver and silicon/titania composite were also synthetized and the main research contents include:?1? Synthes is of the nanoporous silicon. The nanoporous silicon with a large specific surface area ?252.5m2/g?, high pore volume ?1.06cm3/g?, average pore size ?20.13nm? was prepared from rice husks by the optimal method of the best mixture of SiO₂Mg ?molar ratio of 1:2.2?, ramp rate of 1?/min, and 5 hours holding time and it was found that the specific capacity and the Coulombic efficiency of lithium battery reache to 3051.1 mAh/g and 60% for the first time at 100mA/g, and then at 200mA/g, it could still maintain specific capacity at 850.1mAh/g after 100 cycles. In addition, the average reversible capacity of 547.6mAh/g was achieved at 2A/g, exhibiting an excellent electrochemical performance.?2? The silicon/silver and silicon/titania composite materials were synthetized by etching in the mixed solution of silver nitrate and hydrofluoric acid and the way of titania sol-gel, respectively. Through the electrochemical analysis, the silicon/silver composite shown the higher Coulombic efficiency but the capacity faded rapidly. By contrast, the silicon/titania composite exhibited the poor Coulombic efficiency and the better cycle stability during the cycling process. At last, the relationship between microstructure and electrochemical performanc were investigated.