| Lithium-ion batteries, with the advantages as high voltage, high energy density, good cycling property, low self discharge, have been widely used in mobile communication devices, portable electronics and military equipments. At the moment, LiCoO2 still dominates the lithium-ion batteries cathode material market, but owing to its own shortcomings and resource constraints, there is an urgent need to develop a new cathode material. Due to its low cost, good structure stability, and high specific capacity, the layered multiple cathode material of LiNixCoyMn1-x-yO2 has been regarded as one of the most promising alternative material for LiCoO2. However, some problems, including hard to synthesize, low tap density and low rate capability, restrict the procedure of its commercial availability. The improvement of tap density and electrochemical properties, especially its cyclability at high rate, is the main research target of scientists. In this paper, the researches on lithium-ion batteries and its cathode material especially the layered cathode material LiNixCoyMn1-x-yO2 in recent years were analyzed. Some modification method such as improved synthesis methods, doping and coating were carried out by author to improve the tap density and electrochemical performances of them. The main contents and results of this study were described below:First of all, some synthesis methods for LiNixCoyMn1-x-yO2 were mended. Cathode material powders of layered LiNi1/3Co1/3Mn1/3O2 were synthesized using the method of low-heat solid-state reaction, sol-gel method and hydrothermal method. The evolution of the structural properties and electrochemical performances of LiNi1/3Co1/3Mn1/3O2 were investigated by X-ray diffraction (XRD), scanning electronic microscopy (SEM) and galvanostatic charge and discharge cycle. It was found that the optimum parameters for temper of low-heat solid-state reaction technique were 600℃and 2h, the optimal chelating agent in sol-gel method was oxalic acid and the optimal ratio was 1:2, the optimum conditions for hydrothermal reaction was 160℃and 12h.And secondly, the content ratios of Co, Ni, Mn of LiNixCoyMn1-x-yO2 were optimized. Improved low-heat solid-state reaction method, sol-gel technique and hydrothermal method were used to prepare the several series of layered cathode material LiNixCo1-2xMnxO2 (x=n, n/9, n/10, n/11, n/12, n/13, n/14, n/15, n/16, n/17) for lithium-ion batteries, the content ratio of Co, Ni, Mn of various series materials was ameliorated via XRD, SEM, galvanostatic charge and discharge test. The results implied that the materials LiCo5/9Ni2/9Mn2/9O2, LiCo4/10Ni3/10Mn3/10O2, LiCo5/11Ni3/11Mn3/11O2 and so on exhibited outstanding structural properties and electrochemical performances.Afterwards, LiNixCoyMn1-x-yO2 materials were modified by doping. LiNi1/3Co1/3-yMn1/3MyO2-zNz were prepared using low-heat solid-state reaction method, sol-gel technique, hydrothermal method and so on, with one or more cation (Al, Cr, Fe, Zr, La) and/or anion (F, Cl, Br) doped in the cation (Co) and anion (O) site. The effects of doping on the structure, morphology and electrochemical performances were investigated. XRD tests exhibited that the formation of moliclinic structure improved. SEM results implied the uniformity of particles size was increased. The charge-discharge tests showed that the appropriate doping could greatly improve the performances of the as-prepared materials in rate ability and cycle capability.Finally, the layered LiNixCoyMn1-x-yO2 materials were modified via surface coating. Cathode materials LiNi1/3Co1/3Mn1/3O2 were coated with C and Al2O3. The effects of method, raw material and amount on the structure, morphology and electrochemical performances were investigated. The XRD, SEM and electrochemical evaluation results showed that coating with proper amount of inorganic oxide and elemental could reduce the polarization, improve cyclic stability and high-rate ability of material. |
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