Layered LiNi0.8Co0.15Al0.05O2 cathode materials have been synthesized by co-precipitation methods. The effect of pre-thermal treatment was investigated by thermogravimetric differential thermal analysis. Although X-ray diffraction has confirmed that all diffraction peaks in XRD patterns for samples treated at 500 similar to 750 A degrees C can be a well-indexed hexagonal structure, the status of nickel ions varied. Samples pre-treated at different temperatures show different colors and had various contents of Ni3+ measured by XPS. Powders that heated again at 800 A degrees C under the condition of dried oxygen for 12 h after pre-thermal treatment show different electrochemical performances, which pre-thermal treated at 600 A degrees C had a highest reversible specific capacity about 180 mAh center dot g(-1) and capacity retention of 91.7 % after 50 cycles when cycled at a current density of 0.1 C between 2.5-4.3 V at room temperature. The relationship between the status of nickel ions and electrochemical performance was discussed. On the other hand, the capacity retention rates are 91.7, 96.6, and 98.0 % after 50 cycles at 0.1 C and at 100 %DOD, 80 DOD, and 50 %DOD.