- Title
- Single wall carbon nanotubes in manganese oxides for Li-ion battery system
- Creator
- Wang, Jialong
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2024
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The rapid advancements in smart electronic devices (e.g., electronic watches, toys, cameras) have led to increased demands for lithium-ion batteries with higher energy density and cost-effectiveness. In these batteries, the cathode plays a crucial role, acting as a solid host network for lithium ions in Li-ion batteries, enabling reversible intercalation and deintercalation processes. This study was conducted in collaboration between the University of Newcastle and OCSiAl, aiming for developing the manganese dioxide and single-wall carbon nanotubes (SWCNTs) composites, and understanding their chemical, structural, and electrochemical properties (Li/MnO2 system). Moreover, this research included fundamental studies aimed at comprehending the reasons behind cell failure during cycling in the non-aqueous systems, with a specific focus on investigating the oxidation state of dissolving manganese. The structures of different forms of manganese dioxides and lithium manganese oxides rely on the arrangement of their building block unit, [MnO6]. γ-MnO2, in particular, is a non-stoichiometric intergrowth between Pyrolusite and Ramsdellite, primarily caused by structural defects like Mn3+, structural water, and cation vacancies. SWCNTs emerge as an ideal candidate for incorporation into the cathode material. They have the potential to reduce the usage of low-density conductive agents and facilitate the formation of a more favourable conductive network within the electrode so that increasing the volumetric energy density for the electrochemical cell. The common method to produce γ-MnO2 on the commercial scale is via anodic electrolysis of hot, aqueous acidic Mn(Ⅱ) electrolytes. The properties of electrolytic manganese dioxide (EMD) are influenced by the specific synthesis conditions used, including anodic current density, temperature, electrolyte composition, the choice of substrate and other additives, and further affect the electrochemical performances. This work aimed to introduce SWCNTs to the manganese-based material’s synthesis and improve electrochemical performance in non-aqueous systems. Furthermore, the fundamental studies were conducted about understanding of cell failure reasons during cycling in the electrochemical cell, particularly concerning the oxidation state of dissolving manganese. Firstly, the effects of SWCNTs and electrodeposition current density on the chemical, physical, and electrochemical properties of electrolytic manganese dioxide, both before and after heat treatment (HEMD), have been investigated. The presence of SWCNTs in the electrolysis bath leads to decrease the effective deposition current density. This is because the SWCNTs get trapped on the surface of the EMD by the constant mechanical stirring in the electrolysis bath during the electrodeposition, thereby increasing the effective surface area of the anode. As a result, the presence of SWCNTs lowers the effective deposition current density and decreases the electrodeposition reaction rate during the electrodeposition process. Regarding the chemical composition, the inclusion of SWCNTs in the deposition solution leads to a decrease in Mn(IV) content, combined water content, and cation vacancy fraction of EMD. However, it results in an increase in total manganese content and Mn(III) content, showing a similar trend to the EMD samples prepared at lower deposition current density. The XRD results indicated the SWCNTs embedded samples exhibited a similar structure to the EMD prepared at lower current density. Moreover, the EMD prepared at high deposition current density demonstrated good thermal structural stability, indicating fewer structural transformations occurring after heat treatment. The conductivity test serves as an indicator of the SWCNTs content in the EMD samples, suggesting that lower electrodeposition current densities result in a slower electrodeposition rate, which indicates a higher incorporation of SWCNTs in the final prepared sample. Additionally, the electrochemical performance in the Li-MnO2 system indicates that the capacity of HEMD primarily relies on the effective electrodeposition current density. Higher current densities result in higher capacity but lower cyclability. SWCNTs enhance the structural stability of HEMD in terms of rate performance results. This is attributed to SWCNTs accelerating the conversion of new phases and facilitating lithium intercalation, which positively impacts the overall performance of the HEMD material. Secondly, a modified Swagelok cell with an included sensing electrode is proposed as an in-situ analytical tool for detecting the electrode dissolution, as well as measuring the potential of the individual electrode into a non-aqueous Li-ion system. This technique has been applied to detect dissolution from many Li-ion battery cathode systems, such as LiMn2O4, and MnO2 (polymorphs). For LiMn2O4 and MnO2 systems, results demonstrate that Mn(III) is the dissolution product instead of Mn(II), as shown by most recent studies.
- Subject
- lithium ion battery; cathode material; manganese dioxide; in-situ detection
- Identifier
- http://hdl.handle.net/1959.13/1510573
- Identifier
- uon:56429
- Rights
- Copyright 2024 Jialong Wang
- Language
- eng
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|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 9 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 172 KB | Adobe Acrobat PDF | View Details Download |