Full metadata record
| DC Field | Value | Language |
|---|---|---|
| dc.contributor | Department of Industrial and Systems Engineering | en_US |
| dc.contributor.advisor | Xu, Zheng-long (ISE) | en_US |
| dc.contributor.advisor | Chan, Kang Cheung (ISE) | en_US |
| dc.creator | Chen, Feiyang | - |
| dc.identifier.uri | https://theses.lib.polyu.edu.hk/handle/200/14328 | - |
| dc.language | English | en_US |
| dc.publisher | Hong Kong Polytechnic University | en_US |
| dc.rights | All rights reserved | en_US |
| dc.title | Electrolyte engineering for magnesium rechargeable batteries | en_US |
| dcterms.abstract | Achieving carbon neutrality hinges on the widespread adoption of clean renewable energy sources, which in turn necessitates the development of electrochemical storage devices with high energy density, safety, and cost-effectiveness. To meet decarbonization goals, research is increasingly focused on electrochemical storage systems beyond lithium-ion batteries (LIBs), which face limitations due to scarce lithium resources, safety concerns, and potential environmental impacts. Magnesium rechargeable batteries (MRBs) are promising alternatives owing to magnesium’s abundance, high volumetric capacity, and superior safety. However, the development of MRBs is still in its infancy, with several challenges impeding their practical applications. In conventional electrolytes, Mg²⁺ exhibits a stronger polarizing effect compared to lithium ions, which, along with surface passivation on magnesium metal anode, often result in sluggish diffusion kinetics and suboptimal Mg²⁺ storage performance. Thus, designing electrolytes compatible with both high-capacity cathodes and anodes is crucial for advancing MRBs. This thesis presents a comprehensive study on developing new electrolytes for MRBs. By optimizing the chemical structures of the electrolytes and exploring their interface characteristics, a series of formulations have been developed that enable reversible MRBs with excellent electrochemical performance. This breakthrough is expected to significantly facilitate the commercialization of MRBs. | en_US |
| dcterms.abstract | Firstly, a novel Mg²⁺-conducting solid-state electrolyte (MCE) is introduced, created by directly crystalizing deep eutectic solvents composed of Mg(TFSI)₂ and urea at room temperature for safe and sustainable solid-state magnesium rechargeable batteries (SSMRBs). The abundant amine and carbonyl groups in urea ligands greatly tailored the intermolecular frameworks of MCE, resulting in anion-rich groups within the Mg²⁺ solvation sheath. This structure mitigates surface passivation caused by solvent decomposition that commonly observed in liquid electrolytes, i.e., Mg(TFSI)₂/PC. Consequently, when applied in the Mg//Mg symmetric cells, an appreciable cycle life of more than 120 h at 25 μA cm⁻² can be achieved. The improved electrochemical performance is attributed to the F-rich and porous organic/inorganic hybrid interface layer, which effectively activates Mg metal and facilitates rapid Mg²⁺ transport across the interface. Finally, solid-state Mg//V2O5 full cells were constructed to demonstrate the practical feasibility of MCE, achieving a high capacity of 172 mAh g⁻¹ at 20 mA g⁻¹. This work is anticipated as the way of developing novel solid-state electrolytes for safer MRBs. | en_US |
| dcterms.abstract | Secondly, a cosolvent electrolyte composed of Mg(TFSI)₂ salt combined with ethylene glycol (EG) and 1,2-dimethoxyethane (DME) cosolvents is investigated. This formulation tackles the issues of sluggish Mg²⁺ desolvation at cathode-electrolyte interface (CEI) and the TFSI⁻-induced surface passivation in typical Mg(TFSI)₂/DME electrolyte. Hydroxyl-rich EG molecules destabilize unfavorable [Mg(DME)₃]²⁺ complexes and form hydrogen bond networks, thereby facilitating Mg ion migration and suppress TFSI⁻ decomposition. As a result, the co-solvent electrolyte achieves a high reversible capacity of 258 mAh g⁻¹ for VO₂ cathodes, with an exceptionally low capacity degradation rate of 0.0078 % per cycle over 2000 cycles at 500 mA g⁻¹, comparable to state-of-the-art Mg ion battery cathodes. The practical applicability of this electrolyte is further demonstrated by Mg//VO₂ full cells, which maintain capacities above 160 mAh g⁻¹ over 50 cycles. This work establishes a new benchmark for effective electrolytes in MRBs, offering both long cycle life and high energy density. | en_US |
| dcterms.abstract | Thirdly, a novel sulfolane hydrated eutectic electrolyte (HEE) consisting of optimized ratios of Mg(ClO4)₂·6H₂O and sulfolane (SL) is explored, which can comprehensively reduce V2O5 cathode dissolution and achieve a stable and high capacity output for MRBs. In bulk electrolyte, the S=O group in the sulfolane disrupts the continuous hydrogen bonding network among water molecules, thereby reducing water activity. Additionally, its participation in Mg²⁺ solvation structure decreases interfacial bound water content and facilitates Mg²⁺ de-solvation at the CEI. Furthermore, sulfolane’s preferential adsorption on the CEI protects V2O5 from water exposure, strengthening the structural stability of the cathode. As a result, the optimized HEE enables V2O5 cathode to achieve a high capacity of 322.7 mAh g⁻¹ at 50 mA g⁻¹ and exceptional lifespan lasting for over 5000 cycles with a minimal capacity degradation rate of 0.0061% per cycle at 1000 mA g⁻¹. As a proof of concept, a full PTCDA//V2O5 battery with HEE demonstrates a capacity exceeding 190 mAh g⁻¹ for over 200 cycles. This electrolyte represents a new avenue for developing high-energy and high-stable multivalent ion batteries. | en_US |
| dcterms.extent | xix, 129 pages : color illustrations | en_US |
| dcterms.isPartOf | PolyU Electronic Theses | en_US |
| dcterms.issued | 2025 | en_US |
| dcterms.educationalLevel | Ph.D. | en_US |
| dcterms.educationalLevel | All Doctorate | en_US |
| dcterms.LCSH | Storage batteries -- Materials | en_US |
| dcterms.LCSH | Electrodes | en_US |
| dcterms.LCSH | Magnesium | en_US |
| dcterms.LCSH | Hong Kong Polytechnic University -- Dissertations | en_US |
| dcterms.accessRights | open access | en_US |
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