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A study on multilayered MXenes for rechargeable battery electrodes through surface termination control
In the transition from fossil fuels to renewable energy sources, the demand for rechargeable batteries is rapidly increasing. To meet this demand, a diversification of battery chemistries will be essential, due to limited abundance of currently used battery materials. In addition to Li-ion batteries...
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| Format: | Dissertation |
| Language: | English |
| Online Access: | Request full text |
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| Summary: | In the transition from fossil fuels to renewable energy sources, the demand for rechargeable batteries is rapidly increasing. To meet this demand, a diversification of battery chemistries will be essential, due to limited abundance of currently used battery materials. In addition to Li-ion batteries (LiBs), rechargeable Mg batteries (RMBs) stand out as a theoretically promising battery chemistry, with the potential to yield high energy batteries based on abundant materials. However, to enable practical RMBs, competitive cathode materials need to be established. Potential candidates may come from the family of two-dimensional transition metal carbides and nitrides known as MXenes, which due to their high electrical conductivity, chemical tunability and ion intercalating properties, have been predicted to yield high intercalation capacities for a range of cations, including Mg-ions. Hence, this study aimed towards evaluating the feasibility of MXenes for rechargeable battery electrodes, and in particular for RMBs.
In the first paper of this work, the feasibility of MXenes as an RMB cathode was investigated by using two different MXene compositions: V2C and Ti3C2. To ensure the possibility for Mg-ion desolvation and migration, these electrodes were galvanostatically cycled in cells with four different electrolytes, and at both low (20 oC) and high (60 oC) temperatures. Still, only minimal capacities were obtained, indicating insignificant reversible Mg-intercalation in the MXene particles. However, by including Li-salts to the electrolyte, significant reversible capacities were measured, demonstrating the functionality of the MXene electrodes. To explain this difference, density functional theory (DFT) calculations were implemented and showed that the migration barriers for Mg-ions were significantly higher than for Li-ions, and that the termination groups attached to the surface of the MXene sheets strongly influenced the intercalation voltages for Li and Mg-ions. Denoted as "T" (i.e. V2CTx), these termination groups usually consist of a mixture of OH, O and F, and the DFT calculations showed that multilayered particles of O-terminated MXenes would be ideal for RMB cathodes. Hence, the focus of this work was directed towards controlling the termination groups of MXenes, and especially towards substituting F- with O-terminations.
In the second and third paper of this work, gas hydrolysation was explored as a post etching treatment to substitute F-terminations |
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