Local structure-redox relationship in Li-excess layered oxides
- Kipil Lim.
- [Stanford, California] : [Stanford University], 2019.
- Copyright notice
- Physical description
- 1 online resource.
Also available at
- Lim, Kipil, author.
- Chueh, William, degree supervisor.
- Toney, Michael Folsom, degree supervisor.
- Lindenberg, Aaron Michael, degree committee member.
- Stanford University. Department of Materials Science and Engineering.
- In the last decades, lithium-ion batteries (LIB) have significantly contributed to technological progress. Recently, Li-excess layered materials are attracting interest as a promising cathode material for the next generation, since they exhibit high energy densities and capacities significantly higher than commercially available cathode materials. Unlike conventional layered oxides where the only redox center is transition metal cations, an oxygen anion redox in the Li-excess layered material plays an important role to achieve high capacity. However, despite their promising performance, a deeper understanding about the origin and details of anion redox is necessary for commercialization. Understanding the state of the material is crucial as property of material is determined and can be changed by structure. I introduce various X-ray techniques to understand and analyze the structure of Li-excess materials. Rietveld refinement reveals an increase in structural distortion, including antisite defect, in the Li-excess material during anion redox. A strong correlation between structure distortion and anion redox is identified and suggested as a powerful indicator to estimate the existence of anion redox. Not only as an indicator, exact analysis of crystal structure and oxidation state suggest methods to understand the anion redox in Li-excess material. Anion redox can also be tuned by altering composition and crystal structure of Li-excess material. Different amount of Sn substitution in Li1-xIri-ySnyO3 material change the extent of anion redox. Operando X-ray absorption spectroscopy analysis support different electrochemical behaviors. XRD analysis confirmed a distortion in the crystal structure in the existence of oxygen redox. Density functional theory simulation predicts possible local structure as a result of distortion, which suggests multiple ways of oxygen oxidation in different situations. Not only doping for changing oxygen redox properties, changing the synthesis condition affect anion redox strongly. Different annealing temperature and partial oxygen pressure during synthesis do not affect transition metal redox property in Li2RuO3 material. However, difference in synthesis conditions only alters anion redox capacity. I confirm and suggest that crystal structure determine the anion redox property in the Li-excess material, which suggests that we can tune the oxygen redox in various methods, adjust doping or changing synthesis conditions. Over this thesis, systematic analysis of various Li-excess material will be revealed. Study on identifying the structure-property relation is suggested, and methods to control anion redox is verified. This study will suggest powerful and robust direction to understand the origin of anion redox in Li-excess materials. This study will also show a guideline for optimizing properties of cathode materials for next-generation batteries.
- Publication date
- Copyright date
- Submitted to the Department of Materials Science and Engineering.
- Thesis Ph.D. Stanford University 2019.