Study On Synthesis And Properties Of Manganese-based Cathode Materials For Lithium-ion Batteries

Lithium ion batteries as a new energy material are attracting tremendous attentions for their superior properties such as high voltage, high energy density,high-speed discharge, low self-discharge, low toxicity, and so on. At present,searching for the alternative new energy resources and materials used for energy storage have become one focal point of scientific studies conducting, therefore the lithium ion battery cathode material is especially important. Spinel LiMn₂O₄ material becomes the hot spot of the lithium ion battery studies because it has many advantages such as rich raw material resources, easy preparation and environmental friendly and so on. Moreover, Li(Ni_1/3Co_1/3Mn_1/3)O₂ has also been reported to be one of attractive cathode materials in safety and low cost. Investigating a simple,environmental new preparation method is very necessary for the commercialization of the material.The spinel LiMn₂O₄ had been synthesized by hydrothermal precursor method with low temperature and cyclohexanone hydrothermal method. And the factors influencing LiMn₂O₄ synthesized by cyclohexanone hydrothermal method were studied in detail. In addition, a preliminary discussion of some factors influencing the ternary Li(Ni_1/3Co_1/3Mn_1/3)O₂ synthesized by two-step steps has been conducted. The structure and morphology of the samples were characterized by X-ray diffraction（XRD）, scanning electron microscope（SEM） and other test equipments. The synthesis conditions of the the cathode material using different methods were studied, and the electrochemical properties of the samples were tested by the initial charge-discharge and cycle performance tests. It is found that in the process of the hydrothermal precursor method with low temperature, the precursor was synthesized at 120 ℃ in 12 h during hydrothermal stage. And then the product with the excellence electrochemical performance was synthesized from the precursor sintered in 800 ℃for 10 h, and the results demonstrate that the sample prepared with the cyclohexanone hydrothermal of 110 ℃in 8 h, with the Li/Mn molar ratio 1.1:1 and volume ratio of cyclohexanone/H2 O 2:25, and then 100 ℃ insulated for 12 h can have the best electrochemical performance. The optimal conditions in the synthesis process of the ternary Li(Ni_1/3Co_1/3Mn_1/3)O₂/C with the excellence electrochemical performance is that the precursor Ni_1/3Co_1/3Mn_1/3（OH）2 is synthesized at 60 ℃, and next the precursorwith the certain proportion of LiOH·H2O is in 450 ℃ pre-sintering for 4 h, and sintered at 850 ℃for 6 h under argon atmosphere.Although spinel LiMn₂O₄ has many advantages, its poor electrical conductivity has been considered as a limiting factor for using in high-power applications. Another challenge of material LiMn₂O₄ is that the capacity decays significantly with charge-discharge cycling. At the same time, it is also a major problem prohibiting LiMn₂O₄ for commercial application. Coated with carbon is an effective means of modification which is mainly to improve the electrical conductivity of the active materials particles. The effect of different carbon sources, the amount of carbon,calcination temperatures and other factors are discussed by XRD, SEM,electrochemical tests and other test methods. For the cyclohexanone hydrothermal method, the results of the study show that the glucose is the best carbon source, and when the pure LiMn₂O₄ supplemented with 10% glucose, calcined at 600 ℃ for 4 h,the sample exhibits the best electrochemical performance.