Fabrication And Characterization Of Porous Silicia Materials

Lithium iron silicate (Li₂FeSiO₄) is a new lithium ion battery cathode materials with rich resources, low cost, high security and good performance characteristics. It is an ideal cathode material for next-generation lithium-ion batteries. Porous silica (SiO₂) has advantages of low cost, high thermal stability, high structure stability. It is the ideal source material to prepare porous Li₂FeSiO₄. Pores, particular mesopores can significantly improve lithium ion migration rate in Li₂FeSiO₄ and then enhance its electrochemical performance. This thesis maily explores the preparation of porous SiO₂ and ground the preparation of Li₂FeSiO₄ in the next process.In this thesis, the preparation of porous SiO₂, the function of surfactants and performance analysis are the main objects of study. The porous SiO₂ was prepared with different types of surface active agents and composite surfactants, and the performance analysis of product was made systematically.First, the porous SiO₂ was synthetized with inexpensive sodium silicate, hydrochloric acid and surfactant through simple chemical precipitation. On this basis, the effect of the concentration of sodium silicate, hydrochloric acid concentration and pH value on the experiment were determined by trial and error. It mainly discussed the effect of experiment result on the type of surfactants. A series of porous SiO₂ were synthetized with PEG, OP-10, SDBS which can obtain the optimal experimental parameters by using the orthogonal experiment: the concentration of sodium silicate was 0.3 mol / L, the concentration of hydrochloric acid was 1.0 mol / L, and the pH value was 4 of active agents.Second, the porous SiO₂ was synthetized by composite surfactants with the basic of a single surfactant compound. And the effect on different ratio of amount of substance of composite surfactants was investigated. The porous SiO₂ with different forms were made by controlling the ratio of amount of substance of composite surfactants. The optimal experimental parameters were obtained by orthogonal experiments: sodium silicate concentration is 0.3 mol / L, the concentration of hydrochloric acid is 1.0 mol / L, surfactant ratio of amount of substance is 1:1, and the reaction pH value is 4.Finally, the synthesized samples were characterized by the BET test, X-ray small angle diffraction, optical microscopy. The results showed that: the porous SiO₂ specific surface area and the hole orderliness and aperture properties which was made by composite surface active agent was better than which was made by single surfactant synthesis under the porous SiO₂.