Study On Synthesis And Modification Of Cathode Material LiMn₂O₄ For Lithium-ion Batteries

In this dissertation, LiCrxMn2-xO4 cathode materials were prepared via ionothermal and hydrothermal synthesis by using Cr2(SO4)3, LiOH·H2O and MnO2 as sources. The structure and morphology of prepared products were characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and transmission electron microscopy (TEM). And electrochemical performance was studied by charge/discharge test. The main contents and results are as follows:(1) Ionothermal synthesis and properties of rod-like LiCrxMn2-xO4 materialsLiCrxMn2-xO4 materials were synthesized by a novel ionothermal method, using bis-(1-hydroxyethyl) ammonium acetate as the reaction medium at an atmospheric pressure and a low temperature, then followed by heat treatment. The materials were characterized by XRD, SEM and charge/discharge test, respectively. The SEM results indicate that the LiMn2O4 and LiCr0.1Mn1.9O4 materials have rod-like structure with the length of about 1.2 μm and the diameter of about 200 nm. The charge-discharge test demonstrated that a small amount of Cr can effectively improve the electrochemical performance of the materials, and LiCr0.1Mn1.9O4 material has an initial discharge specific capacity of 123.6 mA·h/g at 0.1 C. Furthermore, the discharge capacity of LiCr0.1Mn1.9O4 sample faded slowly before 10 cycles and then remained unchanged in following 50 cycles.(2) Ionothermal synthesis and enhanced electrochemical performance of nanostructure Cr-doped LiMn2O4LiCrxMn2-xO4 (x=0,0.01,0.02,0.05,0.12) materials were effectively synthesized by imidazolium-based ionic liquid as reaction medium at ambient pressure. The materials were characterized by XRD, SEM and charge/discharge test, respectively. SEM results indicate that the LiCro.12Mn1.8gO4 sample has regular and uniform nanosized particles with an average crystallite size of 47 nm. Charge/discharge test reveals that a typical LiCr0.12Mn1.8gO4 delivers the initial discharge capacity of 129.6 mAh g-1 and behaves a quite slow capacity fading with 96.8% of initial capacity remained after 200 cycles at 0.5 C.(3) Hydrothermal synthesis and properties of LiCrxMn2-xO4 materialsLiMn2O4 and LiCr0.2Mn1.8O4 cathode materials were prepared by hydrothermal method, and followed by heat treatment. The results indicate that the initial discharge capacities of LiCr0.2Mn1.8O4reach 115.6,110.2,106.5 and 98.8 mA·h/g at 1,5,10 and 20 C, respectively. The capacity remains about 92.9%、90.1%、88.6% and 86.3%, after 200 cycles, respectively.