X-ray diffraction experiments and accelerating rate calorimetry on the reaction of fully charged Li[Co1−z Al z ]O2 (0≤ z ≤0.15) in PC (propylene carbonate) solvents have been performed. The XRD results show the Li[Co1−z Al z ]O2 samples are in single phase and lie in the range of 0≤ z ≤0.15. The lattice constants vary smoothly with z for these samples, this suggests that the co-precipitation method can produce materials with a uniform cation distribution when the aluminum content is between 0 and 0.15. The impact of Al substitution on the thermal stability of LiCoO2 samples was studied by comparing accelerating rate calorimetry with non substituted sample. The ARC results show the substitution of Al improves the thermal stability of the samples. According to thermal kinetics research, the improved thermal stability is caused by a dramatic reduction in the frequency factor or a change in the reaction model for the reaction.