Synthesis And Modification Of LiNi_xCo_1-2xMn_xO₂ For Lithium Ion Battery Cathode Material

Along with the increase of energy and environment problems, and the rapid development of modern science and technology, how to increase the performances of the lithium ion batteries becomes more and more important. The lithium-ion battery is the first choice for its high energy density, amity to the environment, long cycle life and the high working voltage. Researches on the new cathode materials with low cost and high capacity are the developing trend of conventional cathode materials. As a new generation cathode materials, LiNixCo1-2xMnxO2 cathode material has great potential for being a new kind of cathode candidate for its excellent electrochemical performance and low cost .Firstly, the LiNixCo1-2xMnxO2 cathode material for lithium-ion battery was synthesized by high temperature solid-state method. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to characterize the structure and appearance of the products.The effect of x values,Li/(Ni+Co+Mn) molar ratios,sintering temperatures and sintering times on performances of LiNixCo1-2xMnxO2 were studied, on this basis, the optimized flowsheet was obtained. The results showed that the cycling performance was improved with higher Co content. The cathode material with excellent electrochemical performance was obtained by sintering the mixed raw materials with n(Li)/n(M)=1.10 at 950℃for 20h.The effect of synthesis method, on surface topography, lattice parameter, particle size distribution, specific surface area and electrochemical performance were studied. It was found that the particle size and morphology can be controlled by co-precipitation method. Further studies with different precipitating agent on the performance of LiNi0.4Co0.2Mn0.4O2 had been made. The sample prepared by co-precipitation method with NaOH+NH3 and Na2CO3 as precipitating agent exhibited good properties and Na2CO3 as precipitating agent is more easily carried out for preparation.Layered cathode material was modified by doping method. The anion-doping LiNi0.45Co0.1Mn0.45O2-xFx cathode material was synthesized by high temperature solid-state method. The results showed that when x=0.25, LiNi0.45Co0.1Mn0.45O2-xFx exhibited the initial capacity of 138.58 mAh/g in the voltage range of 3-4.3V, its capacity retained 92.47% after 20 cycles. The cycling performance of LiNi0.45Co0.1Mn0.45O2-xFx had been improved significantly. The cation-doping Li(Ni0.4Co0.2Mn0.4)1-yCryO2 cathode material was synthesized by co-precipitation method. The results showed that when y=0.02, Li(Ni0.4Co0.2Mn0.4)1-yCryO2 exhibited that its capacity retained 90.35% after 20 cycles in the voltage range of 3-4.3V. The cycling performance of Li(Ni0.4Co0.2Mn0.4)1-yCryO2 had been improved.