Reduction of Macro-Porous Silica by the Aluminum for Anode Material of Lithium-Ion Batteries: Effect of SiO₂/Al Ratio.

Macro-porous silicon, which can be used as an anode material for lithium-ion batteries (LIBs), was synthesized by the reduction of macro-porous silica, which had been prepared by template method, using aluminum metal fine powder as the reducing agent. A TEOS-PMMA (tetra-ethyl-ortho-silicate, poly-methyl-meta-acrylate) mixture solution was used as a precursor to prepare the macro-porous silica. PMMA was synthesized as spherical type nano-beads using a suspension polymerization method. Silica gel was formulated by the hydrolysis of TEOS and macro-sized pores were formed in the silica particles by the decomposition of PMMA during the thermal treatment at high temperatures. The prepared macro-porous silica was mixed with aluminum fine powder in methyl alcohol, and then treated at high temperature under argon-gas conditions for the reduction of silica. The silica/aluminum ratio was controlled to 0.5, 0.75, 1.0, 1.5 and 2.0, and the reducing temperature was controlled in the range, 550-700 °C. The formation of silicon was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy.