The Library
Engineering of the manufacture of air-sensitive cathode electrodes for sodium ion batteries
Tools
Roberts, Samuel (2022) Engineering of the manufacture of air-sensitive cathode electrodes for sodium ion batteries. PhD thesis, University of Warwick.
|
PDF
WRAP_Theses_Roberts_2022.pdf - Unspecified Version - Requires a PDF viewer. Download (67Mb) | Preview |
Official URL: http://webcat.warwick.ac.uk/record=b3912173
Abstract
The demand for energy storage devices is ever-growing, especially due to the electrification of transport and increased use of clean but intermittent energy. Sodium-ion batteries are a prospective sustainable alternative to ubiquitous lithium-ion batteries due to the abundance of sodium, and their cobalt-free cathodes. High nickel O3-type oxides show promising energy densities; however, their incorporation into composite electrode slurries containing NMP and PVDF causes a time dependency in the rheological properties, which leads to inhomogeneous coatings being produced. This work aims to assess and engineer the manufacture of electrode slurries containing these high nickel O3-type oxides by understanding the mechanisms behind the time dependent rheological changes, developing tools capable of studying electrode slurries that exhibit changes to their rheological properties over time, and by formulating electrode slurries that have a stable coating window using additives into the slurry mix.
To understand the reasons behind the time dependant rheological changes in the slurry, first a combination of SEM, EDS, and FTIR was used to investigate how the O3-oxide surface changes with exposure to air, demonstrating formation of NaOH on the active material. From the presence of XPS peaks due to NaF it was established that the subsequent gelation of the slurry was initiated by the NaOH, causing dehydrofluorination and crosslinking of PVDF. The electrode slurry gelation, investigated using the novel rheological technique developed for this research, demonstrated three stages likely limited by the concentration of saturated structures.
Secondly, to monitor and map rheological changes with time, a novel oscillatory rheological characterisation method, utilising multiple rapid frequency sweeps and a subsequent fitting to a 2 mode Maxwell model, was developed for this application. Evolution of this technique proceeded through characterisation trials, initially utilising and incrementally adapting rotational rheological methods and, subsequently, advancing through a range of oscillatory methods.
Finally, to stabilise the rheological changes of the slurry, two sets of additives were investigated. The first set, a collection of organic acids, assumed to inhibit the formation of NaOH, were incorporated into the electrode slurries during mixing. Additives of acetic acid and maleic acid led the electrode slurry stabilisation, hypothesised due to the formation of inverse micelles. The final set of additives, which were sodium salts of the first, aimed to increase the electrochemical performance, while maintaining the stabilisation to the electrode slurries. These were assumed to be sacrificially coated onto the active materials using a facile ball milling technique.
The most successful additive was sodium maleate, due to a suppression of the electrode slurry gelation with simultaneous enhancement of the electrochemical performance. These methods and tools developed for sodium ion could also be relevant for other battery types.
Item Type: | Thesis (PhD) | ||||
---|---|---|---|---|---|
Subjects: | T Technology > TK Electrical engineering. Electronics Nuclear engineering | ||||
Library of Congress Subject Headings (LCSH): | Energy storage, Storage batteries, Cathodes, Sodium ion batteries, Energy storage | ||||
Official Date: | June 2022 | ||||
Dates: |
|
||||
Institution: | University of Warwick | ||||
Theses Department: | Warwick Manufacturing Group | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Kendrick, Emma ; Simmons, Mark ; Leigh, Simon J. | ||||
Format of File: | |||||
Extent: | xiv, 241 pages: illustrations | ||||
Language: | eng |
Request changes or add full text files to a record
Repository staff actions (login required)
View Item |