Date of Award
Doctor of Philosophy (PhD)
School of Materials Science and Engineering
Garnet-type LLZOs (Li7La3Zr2O12) with cubic crystal structures are solid-state high Li-ion conductive ceramics, which demand next-generation all-solid-state Li-ion batteries. This garnet group ceramics with high electrochemical performance has been dramatically investigated in recent decades on different aspects, including different doping strategies, novel synthesis for powders and sintering techniques for pellets, defect chemistry modeling, electrochemical performance enhancement, and many others.
This dissertation is centered on fundamentally understanding the composition, structure, thermodynamics of this garnet-type LLZO with various doping strategies. These topics cover general development of garnet-type LLZO in recent years (Chapter 1); Basic theoretical knowledge associated with the research in this dissertation work (Chapter 2); Crystal structure, morphology, and electrochemical properties of garnet with Li-sites and Zr-site doping strategies Chapter 3&Chapter 4; Thermodynamics stability of Ga-doped LLZO and Ta-doped LLZO with DFT modeling and calculation (Chapter 5); Experimental measurement of drop solution enthalpies of these compositions in high-temperature molten solvent calorimetry (Chapter 6); and the final Chapter 7 with a study of engineered sintering process of Ta-doped LLZO with several different sintering oxide aids.
In Chapter 3, the correlation among the composition, structural changes, and morphology of sintered pellets with the varied doping strategies will be investigated. The electrochemical properties, including ionic conductivity and electronic conductivity, will be investigated for both Ga and Ta-doped LLZO at the temperature of 25oC up to 600oC in Chapter 4. In Chapter 5, we have tried to develop a systematic way to build Ga-substituted, and Ta substituted LLZO with Coulomb energy analysis and DFT geometry optimization for total energy calculation. The enthalpy of formation from binary oxides of such garnets with various doping levels was also investigated. In Chapter 6, the high-temperature molten solvent calorimetry was used to measure the drop solution enthalpies of those doped LLZOs; a further investigation involving the composition, structure, and thermodynamical stability of these garnets were deeply explored. The optimized compositions based on the research of thermodynamic stabilities and ionic conductivities in Chapters 3-6 were selected for the engineered sintering study in Chapter 7.
Li, Changlong, "The Effects of Composition on the Structural Symmetry, Ionic Conductivity, and Stability of Garnet-type Li7La3Zr2O12" (2021). All Dissertations. 2881.