Study On Preparation Of Li_xNi_1/3Co_1/3Mn_1/3O₂ Cathode Material And Doping Modification Thereof

Li_xCo_1/3Mn_1/3Ni_1/3O₂ cathode materials were prepared separately by solid-state recation method and oxalate co-precipitation method. The study on doping modification of Li_xCo_1/3Mn_1/3Ni_1/3O₂ was carried out. Influences of the technology parameters on structure, morphology and electrochemical properties of the cathode materials were investigated and discussed.The solid-state reaction method was characterized as that the Li_xCo_1/3Mn_1/3Ni_1/3O₂ cathode material was synthesized at high temperature using transition metal oxides as the reactants. The results indicate that the sample synthesized at 900°C and holding for 12h has a perfect crystal structure and uniform particles, the charge and discharge capacities were 166.8 and 141.1 mAh/g in the voltage range of 2.8⁴.6V at 0.1 C, its cyclic performance was stable.The technology parameters for co-precipitation of Cobalt, Nickel, and Manganese oxalate were optimized, the effects of pH values and temperature on deposition ratio of the metal elements were discussed, influences of calcine temperatures and holding times on the structure, morphology and electrochemical properties of Li_xCo_1/3Mn_1/3Ni_1/3O₂ cathode material were investigated, and the electrochemical performance of the battery under different voltage ranges and discharge rates were compared. The optimum oxalate co-precipitation conditions were pH=8.0, reaction temperature 60°C and the deposition rates of Ni2+,Co2+,Mn2+ were 95.9%,96.1% and 96.3% respectively. The results indicate that the sample obtained at 900°C and held for 15h has perfectα-NaFeO2 crystal structure, the particals are uniform and the shape is spherical. The material could deliver a discharge capacity of 128.8mAh/g even at 1.0C discharge rate in the voltage range of 2.8⁴.3V, after 10 cycles its discharge capacity was 117.1 mAh/g. Its charge and discharge capacities were 194.8 and 156.8mAh/g in the voltage range of 2.8⁴.4V at 0.1C, after 10 cycles its capacity retention was 92.9%. The charge and discharge capacities were 200.3 and 135.7 mAh/g at 0.1C in the voltage range of 2.8⁴.6V, but the cyclic performance was deteriorated, after 10 cycles its capacity retention was 88.1%. So the suitable charge-discharge voltage range is 2.8～4.4V.The doping modification of Li_xCo_1/3Mn_1/3Ni_1/3O₂ was studied, the effects of Fe doping on the structure, morphology and electrochemical properties of the Li_xCo_1/3Mn_1/3Ni_1/3O₂ cathode material were discussed. The results reveal that the Fe doping is benefit for the growth of the crystal grain.The shape of the particles is gradually changed from spherical to non-spherical. The specific surface area decreased from 5.355m2/g(Fe 0%)to 2.869m2/g(Fe 6%) with the increase of Fe content. The initial charge-discharge capacities increased by doping Fe. The charge and discharge capacities were 243.2 and 167.4mAh/g in the voltage range of 2.8⁴.6V at 0.1C when Fe content was 2%.