Study On Preparation And Modification Of LiNi_1/3Co_1/3Mn_1/3O₂ Cathode Material

Lithium ion battery LiLiNi_1/3Co_1/3Mn_1/3O2 cathode material has been found to exhibit good cycle stability performance, high specific capacity, lower cost and higher safety characteristics, and it is one of lithium ion battery cathode material with broad prospect for development.In this paper, LiLiNi_1/3Co_1/3Mn_1/3O2 was synthesized from CH3COOLi·2H2O, Ni（CH3COO）2·4H2O, Co（CH3COO）2·4H2O and Mn（CH3COO）2·4H2O by high temperature solid method, and the physical and electrochemical properties of the material were characterized by X-ray diffraction（XRD）, scanning electron microscope（SEM） and galvanostatic charge-discharge test. The effect of proportions of raw material, temperature and time of calcinations, and Li/（Ni+Co+Mn） mole ratio on crystal structure, morphology and electrochemical performance of the sample of LiLiNi_1/3Co_1/3Mn_1/3O2 was studied. The results showed that the optimum conditions were n（Li）/n（Ni+Co+Mn）=1.1, T=900℃ and t=20h. The LiLiNi_1/3Co_1/3Mn_1/3O2 synthesized under the optimum conditions had favorable structure of hexagonal α-NaFeO2 type and the crystal structure was complete. Its partical size was uniform. It had excellent electrochemical performance. The results of charge-discharge test showed that the initial discharge capacity of this sample was 181.5mAh/g in the voltage range of 2.6V-4.6V at 0.1C. And the capacity retention after 43 cycles was 88.98%.LiLiNi_1/3Co_1/3Mn_1/3O2 cathode material was modified by doping method. The effect of Cr-doping, F-doping and Cr-F-doping on crystal structure, morphology and electrochemical performance of the sample of LiLiNi_1/3Co_1/3Mn_1/3O2 was studied. The results showed that Cr-doping didn’t change the structure of LiLiNi_1/3Co_1/3Mn_1/3O2 and Cr-doping could improve its initial discharge capacity. The sample of Li1.1(LiNi_1/3Co_1/3Mn_1/3)0.95Cr0.05O2 had complete structure. Its partical size was uniform in the range of 300-900 nm. The results of charge-discharge test showed that the initial discharge capacity of this sample was 187.6mAh/g in the voltage range of 2.6V-4.6V at 0.1C. And the capacity retention after 43 cycles was 87.63%.The sample of LiLiNi_1/3Co_1/3Mn_1/3O1.96F0.04 had complete structure and smooth surface. Its partical size was uniform. The results of charge-discharge test showed that the initial discharge capacity of this sample was 181.1mAh/g in the voltage range of 2.6V-4.6V at 0.1C. And the capacity retention after 43 cycles was 93.1%. F-doping could improve the cycle performance of LiLiNi_1/3Co_1/3Mn_1/3O2.Cr-F-doping could improve the electrochemical properties of LiLiNi_1/3Co_1/3Mn_1/3O2. The sample of Li1.1(LiNi_1/3Co_1/3Mn_1/3)0.95Cr0.05O1.96F0.04 had complete structure. The results of charge-discharge test showed that the initial discharge capacity of this sample was 187.4mAh/g in the voltage range of 2.6V-4.6V at 0.1C. And the capacity retention after 43 cycles was 90.34%. The sample showed good electrochemical properties.