- Title
- High performance chemically and physically modified manganese dioxide
- Creator
- Donne, Scott Wilfred
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 1996
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Manganese dioxide is one of the most common primary battery materials used throughout the world due to a unique combination of properties. The world-wide market for batteries incorporating manganese dioxide is estimated to be of the order of $10 billion dollars per year, with electrolytically deposited manganese dioxide (EMD) the material of choice for use in primary alkaline Zn-Mn0₂ cells. Unfortunately, the use of such a large number of primary batteries represents a serious energy and material waste, and it is logical for attention to focus on development of a rechargeable battery system based on the manganese dioxide electrode. This study in the Department of Chemistry at the University of Newcastle, supported by the Australian Manganese Company Limited, was aimed at furthering our understanding of the rechargeability of the manganese dioxide electrode. Birnessite manganese dioxide, modified by the inclusion of Bi³⁺ ions, is a highly rechargeable material that is structurally different to EMD. This and related types of modified material were the topic of this research project. Birnessite manganese dioxide was produced in the project under conditions of controlled pH, Eh and temperature using a completely automated chemostat which was assembled for the project. A range of samples were prepared and then characterized by determining the average manganese oxidation state, the crystallinity (from the XRD pattern) and the primary discharge capacity. Using these techniques, it was concluded that the birnessite sample with the optimum electrochemical performance was prepared under conditions of low pH (pH 5), high Eh (800 mV versus the Ag/AgC1 reference electrode) and high temperature (70°C). These synthesis conditions were then used to prepare a range of Bi-birnessite samples with variable Bi:Mn mole ratios. EMD based electrodes have one fundamental advantage over birnessite electrodes; ie. their density. As a result of EMD being denser than birnessite, it was considered a good candidate for study with dopants, and thus a number of chemically and physically modified EMD samples were prepared, each with a variable Bi:Mn mole ratio. Other dopants such as Pb²⁺, Ba²⁺ and Ti⁴⁺ were also considered briefly. Bi³⁺ was found to be both an effective dopant and to offer less environmental than Pb²⁺, the next most successful dopant. The improvements in performance incurred by introducing Ba²⁺ or Ti⁴⁺ were minimal. The performance of these samples as electrode materials led to the conclusion that there was an optimum dopant level that depended on the type of dopant and the way in which the doping was carried out. Both chemically modified (CMEMD) and physically modified (PMEMD) samples were investigated. The performance of the Bi-CMEMD and Bi-PMEMD electrodes was compared with that of the unmodified EMD electrode when the electrode parameters of graphite concentration, mean graphite particle size and discharge rate were varied. The modified electrodes outperformed the EMD electrode in most cases considered, especially when a high proportion of very fine graphite was used in the electrode (1:1 ratio of Timrex KS6 graphite to Bi-CMEMD or Bi-PMEMD sample). The modified electrodes also performed much better under low drain discharge conditions. To establish how these parameters affect the electrode performance, a detailed understanding of the redox processes that occur in the various manganese dioxide electrodes was pursued. A series of experiments involving slow scan cyclic voltammetry, stationary detector electrode studies, and physical examination of the solid state intermediates by X-ray diffraction were carried out to further our understanding. The results of these experiments allowed interpretation of the improvements in discharge capacity that could be gained by including Bi3⁺ ions in the electrode. They also demonstrated the importance of soluble species (Bi³⁺ and particularly Mn³⁺) in the redox processes. A model for the redox processes occurring in the EMD, birnessite, Bi-birnessite and Bi-CMEMD electrodes was outlined. Overall, it was found that the Bi-CMEMD electrode behaved initially like an EMD electrode. However, in subsequent cycles its behaviour was very similar to that of a Bi-birnessite electrode, which offers substantial reversibility. Finally, the results of these experiments have implications for the production of a commercially viable battery based on the modified manganese dioxide electrode.
- Subject
- batteries; EMD; rechargeable material; Australian Manganese Company Limited
- Identifier
- http://hdl.handle.net/1959.13/1417787
- Identifier
- uon:37252
- Rights
- Copyright 1996 Scott Wilfred Donne
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 266 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 8 MB | Adobe Acrobat PDF | View Details Download |