Abstract
Lithium (Li), a pivotal element in contemporary rechargeable batteries, has experienced unprecedented demand with the rise of electric vehicles, portable electronics, and renewable energy storage systems. This trend further accelerated the concern of global land Li reserves as well as massive energy consumption and environmental pollution caused by traditional large-scale exploitation process, either hard rock mineral deposits or brine deposits. Recognizing the vast untapped potential of Li reserves in the ocean, estimated to be four orders of magnitude greater than on land (approximately 2300 billion tons), and devoid of geographical constraints, this thesis introduces renewable-powered seawater Li extraction systems, aiming for the sustainable and co-friendly extraction in both Li and energy sources.Initially, an innovative unassisted photoelectrochemical (PEC) Li extraction system is presented based on an III-V-based triple-junction (3J) photoelectrode and a Li+ selective membrane, powered solely by sunlight. A decoupling strategy for light-harvesting and catalysis was employed, resulting in the 3J photoelectrode with superior light absorption and catalysis reaction capabilities, and superb stability over the 840 h of the extraction process. It allows the system to successfully enrich seawater Li by 4,350 times (i.e., from 0.18 ppm to 783.56 ppm) after three extraction stages. The overall reaction of the unassisted PEC green Li extraction system achieved 2.08 mg kJ-1 of solar-to-Li efficiency and 3.65% of solar-to-hydrogen efficiency.
Secondly, another seawater Li extraction process method was introduced, integrating an electrical pumping membrane process with a solar panel system. Three distinct Li+ selective membranes were developed to balance the “trade-off” between selectivity and permeation, meeting the different requirements of each stage. This approach achieved a Li concentration elevation from 0.21 ppm in seawater to an impressive 9,234.9 ppm under sunlight illumination, while significantly reducing interference ions. The time required for the Li extraction process was shortened by half, and the total energy consumption required for enriching Li was reduced by 48% in comparison with that required in a previous study relying on municipal electricity.
lastly, we demonstrated a self-powered Li extraction system that capitalizes on ocean wave energy. This system comprises a swing-structured fur-based triboelectric nanogenerator (SSF-TENG) coupled with a Li extraction electrolysis cell to continuously mine Li from seawater. By optimizing the energy storage component and calibrating the output of the SSF-TENG, we ensured compatibility with the energy requirements of the electrolysis cell, thereby maximizing Li production efficiency. The system can enhance Li production from seawater by 60-folds with a high purity of 96 % after three extraction stages. Following an evaporating process, battery-grade Li2CO3 was precipitated with a recovery rate of 77 %.
This thesis presents groundbreaking methodologies for Li extraction from seawater, leveraging renewable energy sources and innovative technologies. The proposed systems not only address the imminent challenges of Li scarcity and environmental concerns but also set new efficiency benchmarks. By harnessing sunlight and ocean wave energy, these methods offer a sustainable and eco-friendly approach to Li extraction, potentially revolutionizing the energy storage industry. The research underscores the importance of interdisciplinary innovation and paves the way for further advancements in sustainable resource extraction and renewable energy integration.
| Date of Award | 22 Apr 2024 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Jr-Hau HE (Supervisor) |