Lithium loss from lithium cobalt oxide: hexagonal Li0.5Co0.5O to cubic Li0.065Co0.935O phase transition

Abstract

Lithium loss from LiCoO₂ following isochronal thermal treatment for 5 h in the temperature range 850–1300°C was determined by thermogravimetric (TGA) and diffractometric (XRD) measurements. Lithium vaporization starts from 900°C, and following thermal treatment at 1300°C 85% of lithium was lost. At 1050°C a change in the mechanism of lithium and oxygen evaporation was observed. Initially, following lithium loss, Li_yCo_2−yO₂ (solid solution of CoO in LiCoO₂) was formed. An activation energy of 305 kJ mol⁻¹, not too far from the heat of reaction from Li₂O to Li₂O₂ vapour, was obtained. Phase transition to cubic Li_0.065Co_0.935O structure occurred starting from thermal treatment at 1050°C. Both hexagonal and cubic lithium cobalt oxide structures were subjected to phase transition to get LiCoO₂ and Co₃O₄ during cooling, but the cubic phase was stabilized against phase transition with increasing temperature.