Synthesis And Modification Of LiNi_1/3Co_1/3Mn_1/3O₂Cathode Material For Lithium-ion Batteries

Ternary complex LiNi_1/3Co_1/3Mn_1/3O₂is considered to be one of the most promisingcandidate cathode materials to replace LiCoO₂for lithium-ion battery （LIB）. As theLiNi_1/3Co_1/3Mn_1/3O₂form the solid solution system of LiCoO₂/LiNiO₂/LiMnO₂, there areobvious positive synergistic effects, with its advantages of high capacity, low cost andfriendly to the environment. And now it is becoming the research hotspot in the new materialof energy in the world. First, an overview of the development of LiNi_1/3Co_1/3Mn_1/3O₂has beengiven in this thesis. Based on this, LiNi_1/3Co_1/3Mn_1/3O₂was synthesized by co-precipitationmethod, and modified by doping the elements of Mg, Zn and Ti. Then the structures,morphologies and electrochemical performance of the modified LiNi_1/3Co_1/3Mn_1/3O₂cathodematerials were characterized by X-ray diffraction （XRD）, scanning electron microscopy（SEM） and the charge and discharge measurement, respectively. The effects of several factors,such as the amout of elements, different element and doping instead of different element ontap density, structures and electrochemical performance of the cathode materials, have beeninvestigated.Doping compounds MgSO₄and C₄H₆O₄Zn were introduced in the process ofco-precipitation, LiOH·H2O and the precursors with Mg and Zn were mixed and calcined（500℃and then900℃） and then the modified cathode materials LiNi_1/3-xCo_1/3Mn_1/3MxO₂（M=Mg, Zn, x=1/40,1/20,1/10） were obtained. It is found that cathode materials doped byMg keep the α-NaFeO₂layered structure, while there are some impurity phase in the cathodematerials doped by Zn, and the more Zn ion were added, the more obvious it became. Thecycle performance of the modified cathode materials will be improved. Among these cathodematerials, LiNi_1/3^-1/20Co_1/3Mn_1/3Mg1/20O₂and LiNi_1/3^-1/40Co_1/3Mn_1/3Zn1/40O₂show betterelectrochemical performance. Their first specific discharge capacity are145.35and131.13mAh·g^-1at the rate of0.1C in the potential range of2.7-4.3V, respectively, which is lowerthan LiNi_1/3Co_1/3Mn_1/3O₂. And their first specific discharge capacity are122.75and119.91mAh·g^-1, and the capacity retention is90.36%and96.53%up to30cycles, respectively, at the rate of1C.First, the precursors, LiOH·H2O and TiO₂were mixed and calcined （500℃and then900℃）, and then the modified cathode materials LiNi_1/3-xCo_1/3Mn_1/3Ti_xO₂（x=1/40,1/20,1/10） were obtained. It is found that the modified cathode materials remain the α-NaFeO₂layered structure, while their cycle performance are improved. LiNi_1/3^-1/20Co_1/3Mn_1/3Ti1/20O₂shows the best electrochemical performance, with its first specific discharge capacity are142.19mAh·g^-1at the rate of0.1C and138.35mAh·g^-1at the rate of1C, respectively, in thepotential range of2.7-4.3V. And the capacity retention is91.83%up to30cycles at the rateof1C.LiNi_1/3Co_1/3^-1/40Mn_1/3Ti_1/40O₂and LiNi_1/3Co_1/3Mn_1/3-1/401/40O₂cathode materials weresynthesized also by co-precipitation method. Both of them remain the α-NaFeO₂layeredstructure and the good crystalline patterns. Among the three modified cathode materialsdoped Ti partly instead of Ni, Co and Mn, LiNi_1/3Co_1/3Mn_1/3-1/401/40O₂shows the bestelectrochemical performance. The first specific discharge capacity of modified cathodematerials LiNi_1/3Co_1/3Mn_1/3-1/401/40O₂are145.35,140.79and125.60mAh/g at the rate of0.1C,1C and2C, respectively, in the potential range of2.7-4.3V. And the capacity retention is88.06%after30cycles at the rate of1C.