Investigation Of Preparation And Doping Of Lithium-nickel-manganese Oxides Cathode Materials

Lithium-ion batteries are most promising high power secondary batteries due to its advantages of higher energy density, more safety, longer lifetimes and no pollution over conventional battery systems. As the demand for better performance of lithium-ion batteries increases, finding new materials capable of improvement on existing technology is one of important methods. Lithium cobalt oxide has been widely used as a cathode material for commercial secondary lithium-ion batteries. But the development of lithium-ion battery is inhibited because of scarcity of cobalt resources, toxicity and unfriendly environment. Based on a merit of solid solution with the formula LiNi1-XCoXO₂ which combines the advantages of cobalt and nickel system materials and the partial substation of Ni with Co can stabilize the lithium nickel oxide structure, within this body of work, layered LiNi_0.8Co_0.2O₂ is synthesized by co-precipitation method. The major performances of LiNi_0.8Co_0.2O₂ at different pH values of solution, calcined temperature, calcined time, and lithium salt content were studied. The structure and electrochemical performance of cathode materials were systematically characterized by a combination of techniques which are TG-DSC, XRD,EIS,CV and SEM.The results show that LiNi_0.8Co_0.2O₂ exhibits a higher discharge capacity of 190mAh/g and good cycle performance at the pH value of 11, the calcined temperature of 900℃, the calcined time of 6 hours, and LiOH/M(OH)₂=1.05.In order to improve performance of material, layer LiNi_0.8Co_0.2O₂ is doped by different dopants .The variation of the cell parameters and volume at different charged voltages of Li[Ni_1-x-yCo_xM_y]O₂(M=Al,Mn)shows that the contraction of cell volume of Al doped is smaller than that of Mn doped, The contraction is smaller and the structure is more stable with increasing Al content. DSC results show that the addition of Al and Mn improve the thermal stability of materials. With increasing amounts of dopant, the decomposition temperatures increase gradually. The effect of Al on the thermal stability is better than that of Mn.