| In the modern society, with the excessive consumption of petroleum energy, global warming and environmental pollution problems, the traditional fossil fuels could not meet the requirements of the rapid development of global economy gradually. Therefore, the studies and applications of lithium-ion batteries have become a world wide topic. Lithium-ion batteries are characterized by high energy density, large charge/discharge capacity, long cycle life and good security, the performance of lithium batteries are largely depend on their cathode materials.Lithium-rich layered oxide materials(LLOs) xLi2MnO3-(1-x)LiMO2(M=Mn, Ni, Co, Fe, Cr,etc.) have been paid much attention about their super high charge/discharge capacity and low cost. These cathode materials have special microstructures and new reaction mechanism. However, there are numerous scientific challenges, such as low initial Coulombic efficiency, poor rate capability, and voltage degradation during cycling, all of above issues need to be solved. Based on such materials, the main contents of this thesis are as follows:(1) Lithium-rich Mn-based layered cathode material was synthesized by solution combustion method and then was calcined at different temperatures to obtain Li1.25(Fe0.3Mn0.7)0.75O2, and its crystal structure, morphology and electrochemical properties were characterized. XRD analysis revealed that the prepared sample behaves the typical layered a-NaFeO2crystal structure, SEM indicated that Lii.25(Fe0.3Mn0.7)0.75O2have irregular shape with agglomerate particles (100-500nm), The electrochemical tests indicated that the500℃-calcined material provides a discharge specific capacity of182mAh/g in first cycle, initial Coulomb efficiency was78.2%, it had improved greatly compared to existing reports. Its initial discharge specific capacity decreased gradully followed by the rising calcination temperature, its cycling performance and rate capability were poor.(2) Doping with Ni2+and Lii.25(Fe0.3Mn0.5Ni0.2)0.75O2was synthesized by solution combustion method. After calcination at different temperatures, the results showed that with the introduction of the Ni2+, electrochemical properties of these materials has been significantly improved, its initial discharge capacity was up to206.9mAh/g, while also showing increasing temperature initial discharge capacity decline. Accordingly, the cycle performance and rate performance was also improved. This is not only because of the introduction of Ni2+can participate reversible oxidation-reduction reaction to improve the specific capacity of the material, and also can suppress the Fe3+into the lithium layer effectively, reduced the phenomenon of mixed cationic and stablelized the crystal structure. And its elongated morphology appeared rice-like particles, which were different that not introduced element Ni.(3) Compared with the type of materials prepared by solution combustion method and sol-gel method, we could have the following conclusions:a) From the aspect of the crystal structure, the material which was synthesized by solution combustion had a more obvious Li2MnO3monoclinic layered structure, and as the temperature rised, the degree of crystallinity also increased accordingly, b) From the aspect of morphology of the materials, the materials which was synthesized by solution combustion of the sample particle size was smaller and the specific area was larger than the sample which was prepared by sol-gel method, and the particles that sol-gel method produced were irregular polyhedron shape, while the sample was prepared by the solution combustion method appeared the slender rice-like particles, and as the calcination temperature rised, grain size become larger and larger, c) The materials prepared by solution combustion method was superior to the first discharge capacity of the sol-gel method, but its circulation efficiency and rate performance were slightly worse than the sol-gel method, d) By comparing the experimental and comprehensive analysis could be obtained that by using a solution combustion synthesis, Li1.25(Fe0.3Mn0.5Ni0.2)0.75O2cathode material calcined at700℃had the best electrochemical performance. Moreover, the solution combustion method was a time-consuming short, low cost, high efficiency preparation, there was much room for improvement in future studies.
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