Passivation of the negative electrode in lithium-ion batteries : lithium fluoride in the solid-electrolyte interphase
Abstract/Contents
- Abstract
- Lithium-ion batteries have become the standard in rechargeable batteries for both portable electronics and electric vehicles because of their high energy and power densities. The solid-electrolyte interphase (SEI) on the negative electrode of these batteries is critical for their performance: it must allow lithium ions to pass while providing a barrier between other reducible species in the electrolyte and the highly reducing electrode, while maintaining the conduction of lithium ions necessary for battery operation. However, in commercial battery production it is often left to form adventitiously on the battery's first charge, optimizing the charging conditions rather than the chemical identity of the layer. As a result these SEIs consist of a complex mixture of organic and inorganic reduction products, a large part of which cannot fulfill the main three functions of an SEI: (1) electronic insulation, (2) impermeability to solvent and electrolyte species, and (3) lithium-ion conductivity. In this thesis it is shown that a simplified SEI primarily composed of lithium fluoride (LiF) can perform these functions, mimicking the beneficial function of an SEI. Furthermore it is shown that LiF can efficiently be deposited by the electrochemical reduction of hydrogen fluoride (HF), small quantities of which are known to be present in battery electrolytes due to hydrolysis of the electrolyte salt lithium hexafluorophosphate. The deposition of this thin layer is characterized and optimized using a simplified electrolyte chemistry on metallic electrodes. 19F-Nuclear magnetic resonance (NMR) spectroscopy is introduced as a useful tool for studying the production of HF in LiPF6-containing electrolytes. Using NMR it is shown that the hydrolysis reaction is strongly dependent on the ion pairing, and that it is greatly slowed in the absence of the lithium ion. The NMR signal for HF is studied in detail, and the expected H-F coupling is observed at low concentrations in the absence of water. A facile way to precisely control the concentration of HF in non-aqueous lithium-ion battery electrolytes containing lithium hexafluorophosphate is presented and benchmarked. The effective removal of adventitiously formed HF in these electrolytes by 3-A molecular sieves is demonstrated, which enables an HF-free LiPF6-based electrolyte for the first time. Subsequently the synthesis, drying, and quantification of anhydrous hydrogen fluoride in non-aqueous solvents was developed and characterized, yielding precise control over the concentration of HF and the following electrodeposition of LiF. Using these techniques the electrodeposition of LiF can be finely controlled. The resulting thin layer can fulfill the main functions of the SEI without excess loss of lithium, clearing the way for more efficient SEI formation in commercial lithium-ion batteries.
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 | 2018; ©2018 |
| Publication date | 2018; 2018 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Author | Van den Berg, Matthijs Pepijn |
|---|---|
| Degree supervisor | Chidsey, Christopher E. D. (Christopher Elisha Dunn) |
| Thesis advisor | Chidsey, Christopher E. D. (Christopher Elisha Dunn) |
| Thesis advisor | Cui, Yi, 1976- |
| Thesis advisor | Waymouth, Robert M |
| Degree committee member | Cui, Yi, 1976- |
| Degree committee member | Waymouth, Robert M |
| Associated with | Stanford University, Department of Chemistry. |
Subjects
| Genre | Theses |
|---|---|
| Genre | Text |
Bibliographic information
| Statement of responsibility | Matthijs Pepijn Van den Berg. |
|---|---|
| Note | Submitted to the Department of Chemistry. |
| Thesis | Thesis Ph.D. Stanford University 2018. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2018 by Matthijs Pepijn Van den Berg
Also listed in
Loading usage metrics...