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

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 deg C - for solid state routes - to 600 deg C. To obtain the HT-LCO compound by a chemical route at moderate calcination 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 deg C to be pure and to crystallize in the desired space group. However, for the calcination temperature of 800 deg 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 deg 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. (author)