Doctor of Philosophy

dissertationElectric vehicles using on-board electricity as a power source have been commercialized for application in a small part of the automobiles market. For wide substitution of the current gasoline-powered vehicles, a lot of effort should be placed on improving the performance of lithium-ion batteries (LIBs), which are the dominant power sources of recent groups of electric vehicles. In this work, we studied several promising cathode and solid-state electrolyte materials for realization of high-capacity, high-safety LIBs. Poly-anionic LiFePO4 and Li2FeP2O7 have been considered very promising cathode materials for LIBs. They have large specific capacities, high thermal and chemical stability, and low cost. However, both of them have the same problem of low ionic and electronic conductivities. In order to speed up the kinetics in the LIBs, these poly-anionic materials were synthesized by developing a simple and high-throughput solution-based technique. The sort of chelating agent and the amount of carbon atoms in the starting solution were varied and the optimal parameters were found for LiFePO4 and Li2FeP2O7, respectively. The safety issue is another important factor for electric vehicles; it is not ensured by current LIBs using organic liquid electrolytes, which are flammable and volatile, prone to leak and decompose at high temperatures. Therefore, recent research has been focused on developing solid-state electrolytes. In this work, high-quality garnet-type iv Li7La3Zr2O12 (LLZO) electrolytes were synthesized using a solution-based technique. The ionic conductivity of cubic LLZO was revealed to be 1.67×10-4 S/cm. A proto-type cell comprised of LLZO electrolyte, LiCoO2 cathode and lithium metal anode was assembled. The cell possessed a gravimetric discharge capacity of 3.4 mAh/g. This value is quite low compared to conventional cells, mainly due to its large interfacial resistance. For improving the interfacial contact, LLZO was fabricated into thin films by pulsed laser deposition technique. The films deposited at room temperature had amorphous structure, and exhibited a lithium-ion conductivity of 3.35×10-7 S/cm. The effects of annealing on the properties of the films were investigated. Films annealed properly were found to have an enhanced lithium-ion conductivity value of 7.36×10-7 S/cm. Moreover, the as-deposited thin films were found to be electrochemically stable against lithium metal