Synthesis And Characteristics Of LiNi_1/3Co_1/3Mn_1/3O₂ Cathode Material For Li-Ion Batterie

LiCoO₂ is the most widely used cathode material in commercial Li-ion batteries. However, along with the development of protable devices and information technology, the need for smaller and lighter battery products promotes the search for new cathode materials. LiNi_1/3Co_1/3Mn_1/3O₂ cathode material attracts so many researchers due to its execellent electrochemical property and thermal stability, as well as its low cost compared with LiCoO₂. In this dissertation, Ni_1/3Co_1/3Mn_1/3(OH)2 was synthesized by hydroxide co-precipitation method and LiNi_1/3Co_1/3Mn_1/3O₂ was obtained by high temperature calcination. The effects of synthesis conditions and calcination on the structural and electrochemical properties of LiNi_1/3Co_1/3Mn_1/3O₂ were studied by means of X ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical measurements, thermogravimetry and the tap-density. Futhermore, the impact of F- during the crystallization of the precursor Ni_1/3Co_1/3Mn_1/3(OH)2 was also concerned.Synthetic conditions, such as pH, amount of chelating agent, rate of dripping, etc. during the preparation of metal hydroxide were investigated. The results showed that, the optimized synthesis condition was pH12.0, the amount of ammonia 0.5mol/L, and the rate of dripping 4mL/min. The initial discharge capacity of 181mAh/g was obtained at a current density of 20mA/g between 2.8⁴.4V and the average discharge capacity retention ratio was 95.6% after 40 cycles.In order to reduce the concentration of liberated Mn2+ and restrain the formation of colloidal Ni_1/3Co_1/3Mn_1/3(OH)2, F- was added to complex Mn2+ separately. The LiNi_1/3Co_1/3Mn_1/3O₂ powder added F- during preparation was characterized. As a result, the colloidal precipition gradually changed to crystalline state as the concentration of F- increased from 0 to 0.15mol/L. However, it can be seen from the SEM images that, lamellar primary crystals agglomerated to form spherical secondary particles, which were loose with many voids, leading to the low tap-density of the LiNi_1/3Co_1/3Mn_1/3O₂ powder. The cycling performance of LiNi_1/3Co_1/3Mn_1/3O₂ was improved after F- was added. The calcination condition was confirmed through TG/DTA test. The effects of calcination temperature and Li/M (M=Ni_1/3Co_1/3Mn_1/3) on the electrochemical properties of LiNi_1/3Co_1/3Mn_1/3O₂ were also studied. The optimal synthesis condition was that Li/M=1.05, sintering 12h at 900℃in air atmosphere.