Abstract: Spherical LiNi_0.5-xCo_2xMn_0.5-xO₂(x=0.075, 0.1, 1/6) powders were synthesized from the co-precipitated carbonate precursor, Ni_0.5-xCo_2xMn_0.5-xCO₃(x=0.075, 0.1, 1/6). The effects of the Co content on the physics and electrochemical performance of LiNi_0.5-xCo_2xMn_0.5-xO₂ were investigated. The SEM images of LiNi_0.5-xCo_2xMn_0.5-xO₂ show that the spherical material consists of many primary particles, which sizes increase with the content of Co increasement. The results of X-ray powder diffraction show that all LiNi_0.5-xCo_2xMn_0.5-xO₂ are pure phase materials with layered structures. The electrochemical tests indicate that the discharge capacities of LiNi_0.5-xCo_2xMn_0.5-xO₂ increase and the cycle performances become better with the content of Co increasing. Under the charge/discharge conditions of 0.2C rate and voltage range of 2.7--4.3V, the discharge properties of spherical LiNi_0.425Co_0.15Mn_0.425O₂, LiNi_0.4Co_0.2Mn_0.4O₂ and LiNi_1/3Co_1/3Mn_1/3O₂ are 145,150 and 158 mAh·g^-1, respectively. The discharge capacity fadings for LiNi_0.425Co_0.15Mn_0.425O₂ and LiNi_0.4Co_0.2Mn_0.4O₂ are less than 3％ , however, there is no fade for that of LiNi_1/3Co_1/3 Mn_1/3O₂ after 50 cycles. The results of AC impedance show that the impedance decreases with the content of Co increasing.

Key words: Li-ion battery, cathode material, spherical, LiNi_0.5-xCo_2xMn_0.5-xO₂