Abstract:Using oxalic acid and stoichiometrically mixed solution of NiCl₂, CoCl₂, and MnCl₂ as starting materials, the triple oxalate precursor of nickel, cobalt, and manganese was synthesized by liquid-phase co-precipitation method. And then the LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials for Li-ion battery were prepared from the precursor and LiOH∙H₂O by solid-state reaction. The precursor and LiNi_1/3Co_1/3Mn_1/3O₂ were characterized by chemical analysis, XRD, EDX, SEM and TG-DTA. The results show that the composition of precursor is Ni_1/3Co_1/3Mn_1/3C₂O₄•2H₂O. The product LiNi_1/3Co_1/3Mn_1/3O₂, in which nickel, cobalt and manganese are uniformly distributed, is well crystallized with a-NaFeO₂ layered structure. Sintering temperature has a remarkable influence on the electrochemical performance of obtained samples. LiNi_1/3Co_1/3Mn_1/3O₂ synthesized at 900 ℃ has the best electrochemical properties. At 0.1C rate, its first specific discharge capacity is 159.7 mA∙h/g in the voltage range of 2.75−4.30 V and 196.9 mA∙h/g in the voltage range of 2.75−4.50 V; at 2C rate, its specific discharge capacity is 121.8 mA∙h/g and still 119.7 mA∙h/g after 40 cycles. The capacity retention ratio is 98.27%.

Key words: Li-ion batteries; cathode materials; LiNi_1/3Co_1/3Mn_1/3O₂; electrochemical performance