Preparation of anatase-type TiO2nanocrystal/acetylene black composites by a dry process, and their electrochemical lithium insertion

Abstract

Composites consisting of anatase-type TiO₂ nanocrystals/acetylene black were synthesized by a novel dry process, involving only the grinding of a mixture of titanium tetraisopropoxide and acetylene black in air for natural hydration, followed by heating. The effects of heating temperature on the formation and properties of the nanocomposite were investigated. The TiO₂ nanocrystal/acetylene black composites could be produced at a temperature of less than 500 °C, with the content of acetylene black decreasing with increasing heating temperature. A single phase of anatase-type TiO₂ could be obtained in the composites at a temperature of less than 400 °C, with the addition of a very minor rutile phase at 500 °C. The crystallization and the size of TiO₂ nanocrystals increases and the dispersion decreases with an increase in the heating temperature. The sizes are 10, 13 and 18 nm for the products at 300, 400 and 500 °C. The amount of lithium inserted in the 1st discharge process depends on the size of the TiO₂ nanocrystals as well as on their crystallization and dispersion. The product obtained at 400 °C gives the highest amount of lithium insertion, having Li/Ti = 0.95 in the solid, and the cell has a markedly high capacity of 319 mAh g⁻¹ at a cutoff voltage of 1 V. The voltage in the discharge curve showed a flat plateau around 1.8 V until Li/Ti = 0.4 after which it decreased. The electrochemical lithium insertion progressed topotactically, even with a large amount of lithium insertion, without any structural change.