The electrochemical phase transformation in LiXFePO4
Abstract/Contents
- Abstract
- Phase separation induces heterogeneity and are common in many industries, such as energy storage, metallurgy, polymers and life sciences. Such heterogeneity, often in the form of spatially distributed phases of different compositions, directly impacts the performance and degradation of a material. For example, in electrochemical phase-separating materials such as lithium ion batteries, the phase separation boundaries has been shown to impact the transport and stress accumulation, thus controls the rate performance and lifetime. Understanding the spatiotemporal electrochemical transformation dynamics is therefore important; but the thermodynamically heterogeneous nature, as well as the non-linear dynamics underlying the non-equilibrium electrochemical reaction kinetics makes this goal challenging. More importantly, in a realistic device operation cycle, fluctuating current is unavoidable, but most of the transient behavior beyond steady current conditions are under-explored. In this dissertation, I demonstrate an approach that integrates advanced characterization, phase field theory and numerical computation to understand electrochemical phase transformation, extending beyond typical constant current conditions. Using LiXFePO4 as a model system, I will break the challenge into two parts based on phase-field theory. First, I will focus on understanding the stress/strain development during phase separation. This allows for a proper construction of the materials behavior at equilibrium. To be specific, the chemo-mechanical constitutive relation that governs the material deformation upon lithiation is extracted through a partial differential equation constrained optimization from correlative images composed of strain and composition. Additional chemo-mechanical insights such as generations of dislocations can be drawn, which may be key to understanding battery lifetime. Having established the equilibrium picture of the material, I will next discuss the transient transformation dynamics beyond constant current conditions. Mechanisms of electrode activation that minimizes resistance through current pulses, as well as the power law relaxation of the metastable solid solution will be discussed. These results provide fundamental insights on optimal battery operation strategies. These findings are generalizable to many other phase-separating systems and demonstrate the potential of merging advanced characterization, phase-field theory, and numerical computation for scientific discovery.
Description
| Type of resource | text |
|---|---|
| Form | electronic resource; remote; computer; online resource |
| Extent | 1 online resource. |
| Place | California |
| Place | [Stanford, California] |
| Publisher | [Stanford University] |
| Copyright date | 2021; ©2021 |
| Publication date | 2021; 2021 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Author | Deng, Haitao |
|---|---|
| Degree supervisor | Chueh, William |
| Thesis advisor | Chueh, William |
| Thesis advisor | Cai, Wei, 1977- |
| Thesis advisor | Lindenberg, Aaron Michael |
| Degree committee member | Cai, Wei, 1977- |
| Degree committee member | Lindenberg, Aaron Michael |
| Associated with | Stanford University, Department of Materials Science and Engineering |
Subjects
| Genre | Theses |
|---|---|
| Genre | Text |
Bibliographic information
| Statement of responsibility | Haitao D. Deng. |
|---|---|
| Note | Submitted to the Department of Materials Science and Engineering. |
| Thesis | Thesis Ph.D. Stanford University 2021. |
| Location | https://purl.stanford.edu/cg353qy9132 |
Access conditions
- Copyright
- © 2021 by Haitao Deng
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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