The Development Of High Capacity Cathode Material For Lithium-ion Batteries

Lithium nickel oxides is a high capacity cathode material for lithium-ion batteries, we synthesized three cathode materials for lithium-ion batteries, LiMxNi_0.8-xCo_0.2O₂,LiNi_1/3Mn_1/3Co_1/3O₂ ,LiNi_1/2Mn_1/2O₂,and studied the performance of those materials, this article is assistance to cathode material with low cost but high power.A series of layer compounds LiMxNi_0.8-xCo_0.2O₂(M=Mg, Al, La, x=0～0.05) were synthesized by solid state reaction with high temperature, the oxygen was needed in this reaction, the temperature was controlled with keeping 12 hours at 800℃.the good cycle performance were got as x=0.05,0.05,0.01 .LiAl_0.02Ni_0.78Co_0.2O₂ and LiAl_0.05Ni_0.75Co_0.2O₂ were not clearly different. XRD pattern of LiMxNi_0.8-xCo_0.2O₂(M=Mg, Al, La) indicated these materials were layer structure.The co-precipitation technology was employed to synthesize the precursor of Ni,Co and Mn hydroxides ,With the precursor mixed with LiOH·H2O in solid state then sintered in air , LiNi_1/3Mn_1/3Co_1/3O₂ can be obtained as cathode material for lithium-ion batteries. Experiments of electrochemistry performance and characteristics of XRD, SEM were carried out. The lattice structure of the material was anα-NaFeO2 layered, hexagonal (space group R3m) . Initial discharge capacities of 173,177,200 mAh·g-1 were respectively obtained in the range of 2.5～4.3,2.5～4.3,2.5～4.7V(current density 18 mA·g-1),and its electrochemical stability descended with the increase of the charge-discharge voltage.The material was charge-discharge at different current density 0.36mA·g-1(0.2C),0.90 mA·g-1(0.5C),180 mA·g-1(1C), the results showed that the material was suited to discharge at larger current. XRD pattern of LiNi_1/3Mn_1/3Co_1/3O₂ indicated that the compound had a good layer structure, R=I003/I104=1.38, the cation mixed degree was lower. We could find that the dominating reason of capacity fading was possibly the resistance increasing of the cathode/solution interface from the EIS pattern. The CV pattern indicated that the material took place two dominating redox reaction. The result of DSC showed that LiNi_1/3Mn_1/3Co_1/3O₂ had a wider radiative apex than LiCoO2 and LiNiO2, and its hot stabilization was better.The precursor of LiNi_1/2Mn_1/2O₂ was synthesized by the co-precipitation technology . Initial discharge capacities of 166.9mAh/g,180.4mAh/g,191.9mAh/g were respectively obtained in the range of 2.5～4.3,2.5～4.3,2.5～4.7V(0.1C),and its electrochemical stability descended with the increase of the charge-discharge voltage.XRD pattern of LiNi_1/2Mn_1/2O₂ indicated that the compound had a good layer structure, R=I003/I104=0.79, the cation mixed degree was acute.