| With the increasing global energy demand, one of specific requirements is positive electrode material with high capacity, high security, low cost and environmental. However, in present cathode materials can’t meet the requirements of the market, cathode materials become the bottleneck of commercial lithium ion batteries, the cathode materials attract more and more researchers’ attention. Recently, Li-rich cathodes have caught the great attention for the novel electrode materials of lithium ion batteries. These materials with low content of cobalt and high Mn content are low cost and lead to interesting capacities, up to 250 m Ah·g-1 or more. The drawbacks of these series of materials are their huge irreversible capacity loss, dramatic capacity fading and poor rate capability, so the weakness limits materials are applied in actual business.Due to such shortcomings of Li-rich cathode material, we have done some works as follows:1. Li-rich layer-structure x Li2 Mn O3·(1-x)Li Ni1/3Co1/3Mn1/3O2(x = 0.4, 0.5,0.6) cathode materials has been synthesized by Self-propagation combustion method, the influence of x value and sintering temperature on morphology and electrochemical properties. The crystal structure and morphology are characterized by X-ray diffraction(XRD), SEM, BET and size distribution and so on. XRD patterns indicate that the assynthesized material is pure and with good crystallinity. SEM and size distribution show the average particle size(200 nm). The charge/discharge results indicate that the Lirich have a good electrochemistry properties are synthesized via Self-propagation combustion method. Within the cut-off voltage between 2.3 and 4.8 V, the initial discharge capacity is 255.0 m Ah·g-1 at 0.1 C rate; and after 100 cycles the discharge capacity remains 214.5 m Ah·g-1, with good reversibility(84 %).2. The morphology and particle size of materials have great effect on the electrochemical performance, in order to better control the morphology and particle size of materials, the O2/N2 mixtures and dispersant(PVP) that introduced during selfpropagating sintering, 0.6Li2 Mn O3·0.4Li Ni0.7Mn0.3O2 was prepared by this method. We mainly studies the following several aspects:(1) Self-propagating sintering in air, selfpropagating sintering in air after adding dispersant(PVP), self-propagating sintering in O2/N2 mixtures after adding dispersant(PVP), it was found that self-propagating sintering in air after adding dispersant with the best electrochemical properties.(2) In order to get better electrochemical performance of Li-rich layered materials, the vacuum distillation method is applied for synthesis of Li-rich materials, the study found that the electrochemical properties of materials are improved after the vacuum distillation. The crystal structure and morphology are characterized by X-ray diffraction(XRD), SEM and electrochemical performance test, the results show that the dispersant improved the reunion of materials.3. To improve the high-rate capacity and cycle ability, we successfully coat the nanoparticles of 0.6Li2 Mn O3·0.4Li Ni1/3Co1/3Mn1/3O2(LMO).(1) Li2 Zr O3-coated: Li2 Zr O3-coated after Li-rich materials sintering at high temperature, study the influence of different coated quantity of Li2 Zr O3 on crystal structure and electrochemical performance. The result shows that Li2 Zr O3-coated can improve the electrochemical properties especially at high-rate.4. To improve the high-rate capacity and cycle ability, we successfully coat the nanoparticles of 0.6Li2 Mn O3·0.4Li Ni1/3Co1/3Mn1/3O2(LMO). Al F3-coated: The method of Al F3-coated were same as previous, studies show that the quality of the coating ratio is 2% has the best high-rate, the electrochemical properties were tested at 55°C.Through the studies of this paper, we have further comprehension of the preparation, structure, morphology and electrochemical performance of Li-rich cathode material. All these provide basic research and practical application for Li-rich cathode material in the future. |
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