Preparation Of LiNi_1/3Co_1/3Mn_1/3O₂ Cathode Materials For Lithium-Ion Batteries And Design Of Soft-Pack Lithium-Ion Batteries

Li-ion batteries(LIBs) is a new-type and environmental friendly battery with high energy density, which was developed on the base of the lithium batteries. It has already become one of the most widely used and promising batteries on account of its high voltage, high capacity, long cycle life and great safety performance. Layered compound LiNi1/3Co1/3Mn1/3O2 has been seen as the substitution of LiCoO2 to be the next generation cathode used in LIBs, which possesses the advantages of high specific capacity, low cost and environmentally friendly integrated the merits of LiCoO2, LiNiO2, and LiMnO2.However, due to the similarity in radius between Li+ and Ni2+, LiNi1/3Co1/3Mn1/3O2 always emerges the Li-Ni cation hybrid phenomenon during the crystallization, which will affect the transfer of Li+and the stability of the crystal negatively. In this thesis, homogeneous LiNi1/3Co1/3Mn1/3O2 nanoparticles were synthesized by electrospinning and sol-gel method, respectively. In order to further reduce the influence of cation hybrid, the Na+, Al3+ co-doped LiNi1/3Co1/3Mn1/3O2 were also synthesize by the electrospinning method. X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques were used to characterize the structure and morphology of the materials. The cyclic voltammetry, constant current charge-discharge method, AC impedance testing were contacted to investigate theircyclic and rate capability. Finally, LiNi1/3Co1/3Mn1/3O2 was used as cathode materials in the soft-pack battery with the environmentally friendly aqueous LA 133 as the binder for anode and cathode. The major research contents and results are as following:(1) The synthesized LiNi1/3Co1/3Mn1/3O2 particles by this two different methods show perfect crystal structure with a size in the range of 50?200 nm. The LiNi1/3Co1/3Mn1/3O2 synthesized by electrospinning possesses the higher crystallinity and lower AC impedance. Its specific capacity can reach over 120 mA h g-1 after 100 cycles at 0.2 C.(2) The material doped moderate Na+ and Al3+ has reduced the cation hybrid level and electrode polarization. Its first discharge specific capacity can be improved from 177.8 mA h g-1 to 213.8 mA h g-1 in comparison with undoped material. The specific capacity increased from 132.2 mA h g-1 and 126.2 mA h g-1 to 153.7 mA h g-1 and 135.7 mA h g-1 after 20 cycles and 50 cycles, respectively.(3) LiNi1/3Co1/3Mn1/3O2 was used as cathode material for the soft-pack LIBs, and the environmentally friendly aqueous LA 133 was selected as the binder for anode and cathode. The first discharge capacity of this battery can reach 343.2 mA h, and the coulombic efficiency is as high as 83.6%. The capacity can reach 245 mA h at 5 C rate. When the condition temperature was tuned to 55 ? and 2 ?,respectively, this battery can release 290.0 mA h and 184 mA h correspondingly without leakage phenomenon or any other accidents, indicating a superior rate performance, long cycle life and great discharge performance under both high and low temperatures.