| This thesis includes four parts. Part one gives some backgrounds about this thesis. In this part, recent developments on lithium fast ion conductors and electrode materials including cathode materials and anode materials for lithium ion battery are reviewed. For cathode materials, layer-structured LiMO2 and spinel-structured LiMn2O4 as well as their derivatives are discussed in detail, other kind of cathode materials such as vanadium oxide, LiNiVO4, olivine-type LiMPO4 are also presented. Focus of anode materials is putting on carbon materials and metallic materials. For lithium fast ion conductors, emphasis is on perovskite-type together with LISICON-type solid state electrolytes. Part two deals with preparation and characterization of new perovskite-type lithium ion conductors. Two new lithium ion solid electrolyte systems of Li3xLa0.67-xTi1-yAlyO3-yFy and Li3x-yLa0.67-xTiO3-yFy prepared by high temperature(1200℃) solid state reaction are characterized by the methods of A.C. impedance, X-ray diffraction, D.C. polarizing and IR measurements. The results show that the Al3+ and F-codoped samples have a better conductivities and higher decomposition voltage compared with their parent material. The results also show that Al3+ and F-codoped samples have higher conductivity than those doped only with F-. The maximum conductivity is 1.06×10-3S/cm at room temperature and 3.01×10-2S/cm at 573K for the initial composition of x=0.11,y=0.02 in Li3xLa0.67-xTi1-yAlyO3-yFy system, its decomposition voltage reaches up to 2.3V. Part three discusses the properties of mineral lithium fast ion conductors based on LiTi2(PO4)3, which have been prepared by conventional solid state reaction using refined natural kaolinite as a starting material. In this part, three mineral lithium fast ion conductor systems of Li1.2+x-yYxTi1.9-xAl0.1Si0.1SyP(2.9-yO(12) (referred as Y-S-Lisicon), Li1.2+x-yAl0.1+xTi1.9-xSi0.1SyP2.9-yO12 (referred as Al-S-Lisicon) and Li1.2+x-yYxTi1.9-xAl0.1Si0.1WyP2.9-yO12(referred as Y-W-Lisicon) were studied. For Y-S-Lisicon system, XRD results show that a R c structure can be found in the composition range of x≤0.3,y<0.2+x . Conductivities and activation energies data show that the initial composition with x=0.1,y=0.15 possesses the maximum ionic conductivity of 2.93×10-5S/cm at room temperature and 3.62×10-2S/cm at 673K. For Al-S-Lisicon system, phase analysis shows that a R c structure can be found in the composition range of x=0.1,y<0.3 and x=0.2,y<0.4. The sample with initial composition of x=0.2,y=0.20 possesses the maximum ionic conductivity of 6.01×10-5S/cm at room temperature and 1.11×10-2S/cm at 573K, its activation energy is 28.60KJ/mol. For Y-W-Lisicon system, a R c structure can be found in the composition range of x=0.1,y<0.2 and x=0.2,y<0.2. A.C. impedance measurements indicate that the initial composition with x=0.1,y=0.10 possesses the maximum ionic conductivity of 1.65×10-5S/cm at room temperature, while at 573K, the initial composition with x=0.2,y=0.10 possesses the maximum ionic conductivity of 6.53×10-3 S/cm. The activation energies of this system are in the range of 41.52KJ/mol ～64.77KJ/mol in the temperature range of 373K ～573K. The decomposition voltage for the above three system is around 3.0 V. These results show that most of lithium fast ion conductors mentioned above are good fast ion conductors with good electrochemical stabilities. Part four is about cation and anion codoped LiMn2O4--LiMn2-xYxO4-yFy as cathode material of lithium ion battery, which has been synthesized by co-precipitation method. X-ray powder diffraction analysis shows that a spinel-structured phase together with other manganese oxides exists in the cathode material. The results of CV measurement show that two couples of redox peaks still appear around 4.0V when doping appropriate amount of Y3+ and F-. ESEM images indicate that the samples sintered at lower temperature have smaller and more homogeneous crystalline grain. The results of charge /discharge experiments of half–cell show that the samples sintered at 600℃possess the best electrochemical performance and that the initial charge capacity decreases with the increasing value of x for the same value of y. Concerning both capacity and cyclic ability, the sample with initial composition of x=0.05, y=0.10possesses the best electrochemical performance, whose charge and discharging capacity reach up to 132.80 mAh·g-1 and 94.84 mAh·g-1 respectively for the 1st cycle and maintain 113.77 mAh·g-1 and 93.83 mAh·g-1 respectively after 15 cycles with total discharge capacity decay of 1.06% for the first 15 cycles when tested at a charging rate of 0.20 mA/cm2 and discharging rate of 0.15 mA/cm2 in the potential range of 3.0-4.5V, which is better than that of undoped spinel LiMn2O4 prepared by the same route. |
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