A STUDY OF IONIC MATERIALS FOR THE ENERGY APPLICATIONS THROUGH FIRST-PRINCIPLES CALCULATIONS AND CALPHAD MODELING

Open Access
Author:
Lee, Sung Hoon
Graduate Program:
Materials Science and Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
June 24, 2011
Committee Members:
  • Dr Zi Kui Liu, Dissertation Advisor
  • Zi Kui Liu, Committee Chair
  • Long Qing Chen, Committee Member
  • Clive A Randall, Committee Member
  • Jorge Osvaldo Sofo, Committee Member
Keywords:
  • Ionic materials
  • energy
  • CALPHAD
  • first-principles
Abstract:
Computational thermodynamics have been steadily demonstrated to provide invaluable insight to identify materials exhibiting desirable properties. Especially, applications to the ionic materials as energy materials are subject to great interest due to their importance in alternate energy source. In the present dissertation, three examples using CALPHAD (CALculation of PHAse Diagram) and first-principles calculations to aid materials design for energy applications are presented: i) (La1-xCax)FeO3-δ perovskite is a potential candidate material for gas separation membrane. The defect chemistry and the energetics of (La1-xCax)FeO3-δ are studied owing to their importance in understanding its electrochemical performance. The interactions of multi-component and mul-tiple-defects are modeled using oxygen nonstoichiometry and the experimental phase equilibrium data. The calculated phase diagrams are in good agreement with experiments, and based on the models developed, the defect chemistry and the underlying energetics of (La1-xCax)FeO3-δ perovskite under various service conditions are predicted in terms of gas composition, pressure, temperature, and Ca content. The developed models hence provide guidance on operational pa-rameters of membranes, solid oxide fuel cells and other applications involving (La1-xCax)FeO3-δ perovskite. i) LiBH4, owing to its high hydrogen density (18wt%), has been widely studied as a possible candidate for the hydrogen storage material. However, it desorbs hydrogen gas at a relatively high temperature (400 oC), and it is believed that strong ionic bonding is the main reason. Since the hydrogen atoms form covalent bond with boron atom, its effect is questionable, and as an effort to elucidate doping effect on the hydrogen desorption temperature, divalent metal-dopants, Mg, Ca, and Zn, on the stability of LiBH4 is studied. Using the model parameters, their dehy-driding reactions are estimated in an effort to elucidate the energetically-preferred reaction me-chanism of metal with LiBH4. iii) LiFePO4 is a promising electrode material for Li-ion battery. Phase transformation and elec-trochemical cell potential during insertion/deinsertion of Li+ ions are crucial properties which dictate the use of this material as an electrode. By using first-principles calculations, discharge voltage and enthalpy of formation are obtained, and phase diagram of the LiFePO4-FePO4 pseu-do-binary system and cell voltage change at a given condition are predicted by thermodynamic modeling.