The influence of synthesis temperature on the HT-LiCoO2 crystallographic properties

Abstract

Much of the success of cobalt-based lithium-ion batteries is due to the easy synthesis of HT-LiCoO2 achieved with sol-gel routes. Many sol-gel routes reduced the synthesis temperature from 900 °C - for solid state routes - to 600 °C. However, to obtain the HT-LCO compound by a chemical route at moderate calcinations temperatures, the heating rate at the early stage of the synthesis should be high. However, at high heating rates, a high concentration of energy develops due to the combustion of chelating agents, causing an undesirable great volumetric expansion. Therefore, as a way of minimizing the volumetric expansion effects the heating rate in the synthesis was investigated. X-ray diffraction results showed that using a low heating rate the HT-LCO phase formation requires more than the energy available at 600 °C to be pure and to crystallize in the desired space group. However, for the calcination temperature of 800 °C, only 20 min was sufficient to synthesize a high ordered crystallographic HT-LCO phase. The reduced synthesis time is possibly associated with a high homogenization of the metallic ions since the gel expansion is radically reduced. The LCO synthesized at 800 C for only 20 min showed electrochemical charge capacity of about 140 mAh g-1. It was concluded that by controlling the kinetics during the heating step, in the early stage of the synthesis, the HT-LCO is obtained with high ordered crystallography, although the synthesis time is reduced, therefore enabling a more economically attractive synthesis process.

Keywords

• lithium batteries
• sol-gel synthesis
• licoo2
• crystallography
• crystallite size
• micro-strain.