Nickel-manganese-cobalt oxide (NMC) cathode materials have been applied in most Li-ion batteries, but there are nevertheless some concerns regarding the stability of this material. High voltage and high temperature during charging have been shown to accelerate the dissolution of NMC due to the release of more acidic components because of rapid electrolyte decomposition. Mn-contaminants (Mn2+) are hypothesized to diminish the diffusion coefficient of Li+ in the electrolyte attributed to the competitive interaction between Mn2+ ions and Li+ ions. With characterizations including 7Li and 1H pulsed field-gradient nuclear magnetic resonance (PFG-NMR) spectroscopy, we demonstrated the Mn (II)-contaminants effect on diffusion coefficient on Li+ dynamics. Under the influence of deliberate manganese salt-additive to the electrolyte, the coin cell shows a capacity fading and unstable charging behavior. The PFG-NMR measurements also validated our hypotheses, as the results showing that Mn-containment causes decrease ~15% in the diffusion coefficient on Li-self diffusion. The activation energy for lithium-ion transport over the temperature range of (273 K - 303 K), was not changed by the presence of the Mn-contaminant electrolyte, which indicates the Mn (II) does not affect the Li-ion transport mechanism. The relative test also includes comparisons with other contamination, such as iron contamination from stain-less steels spacers and copper contamination from the current collector. Additionally, the lithium self-diffusion coefficient was tested before and after charging using a full battery configuration. In electrolytes containing manganese contaminants, a more significant decrease in the diffusion coefficient was observed after charging. Ideally, operando experiments can be used to observe the impact of manganese ions on the SEI. By combining both types of experiments, a closer approximation to the actual application conditions of market-used batteries can be achieved. / Thesis / Master of Science (MSc) / The increasing maturity of lithium battery technology has also promoted the advancement of the electric vehicle manufacturing industry. As an excellent new energy material, the application and development of lithium batteries will be the main trend in the future. However, while improving battery capacity and energy density, lithium batteries also face many challenges.
The entire thesis work discusses how electrolyte degradation at high temperatures and high voltages accelerates the dissolution of transition metal manganese ions in NMC materials. The dissolution of manganese ions into the electrolyte creates a competitive effect with lithium ions, thereby reducing the performance of lithium batteries. Here, NMR technology was used to measure the negative effect of manganese ions on the self-diffusion coefficient of lithium ions in the electrolyte. Additionally, a set of operando experiments conducted at different discharge rates demonstrated the changes in mossy lithium and the solid electrolyte interface during the charge and discharge phases caused by pulse discharge. This also proved that such experimental designs can track the impact of manganese ions on the solid electrolyte interface and test the dissolution behavior and impact of manganese ions under different charge and discharge rates.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/30179 |
| Date | 11 1900 |
| Creators | Zheng, Runze |
| Contributors | Goward, Gillian |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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