| Author: | Liu, Xinlong |
| Title: | Interfacial engineering of zinc anodes for high-performance aqueous zinc-ion batteries |
| Advisors: | Xu, Bingang (SFT) |
| Degree: | Ph.D. |
| Year: | 2025 |
| Subject: | Zinc ion batteries Electrolytes Corrosion and anti-corrosives Hong Kong Polytechnic University -- Dissertations |
| Department: | School of Fashion and Textiles |
| Pages: | xxix, 172 pages : color illustrations |
| Language: | English |
| Abstract: | Although zinc metal anode is promising for zinc-ion batteries (ZIBs) owing to high energy density, the reversibility is significantly obstructed by uncontrolled dendrite growth and parasitic reactions. Additionally, secondary reactions such as hydrogen evolution and corrosion occur on the electrode/electrolyte interphase can severely reduce the conversion efficiency and utilization (coulombic efficiency) of Zn metal. Therefore, the interface between the electrolyte and the electrode in zinc-ion batteries is crucial for the battery's electrochemical performance, efficiency, and longevity. During charging, zinc ions are reduced and ideally deposited uniformly on the zinc electrode. However, due to uneven current distribution and surface irregularities, zinc often deposits unevenly, forming needle-like dendrites that can pierce the separator and cause short circuits, leading to battery failure or safety hazards. The interface plays a vital role in promoting uniform zinc deposition to reduce dendrite formation. Additionally, zinc is prone to corrosion in aqueous electrolytes, forming zinc oxide or hydroxide, which consumes active material and reduces battery capacity. The interface affects the corrosion rate, and protective coatings or electrolyte additives can form a passivation layer to mitigate this issue. Furthermore, in aqueous electrolytes, water can be reduced to hydrogen gas at the zinc electrode, especially at high overpotentials, resulting in hydrogen evolution, which interferes with zinc deposition and decreases the battery's coulombic efficiency. Hydrogen evolution reaction (HER) can also cause gas buildup, increase internal pressure and potentially lead to mechanical failure. By engineering the electrolyte/electrode interface through material selection, surface modifications, and electrolyte formulation, it is possible to suppress HER and minimize dendrite formation and corrosion, thereby enhancing the battery's efficiency, capacity, and lifespan. Firstly, modifying the electrolyte is a simple and effective approach to tackle these problems simultaneously. On the other hand, the pH variation during charge/discharge process has a significant influence on the reaction processes through Zn2+ deposition, HER, and corrosion. Therefore, stabilizing the H+ concentration can simultaneously resolve those issues. In this research study, a multifunctional pH buffer was applied to regulate the reaction process, thereby increasing the anti-corrosion ability and inhibiting dendrite growth. Good's buffers, adopted as a novel additive, are initially introduced into conventional ZnSO4 electrolyte to ensure dendrite-free zinc anode surface, enabling stable Zn/electrolyte interface by controlling the solvated sheath through H₂O poor electric double layer (EDL) derived from zwitterionic groups. Moreover, this zwitterionic additive can balance localized H+ concentration of the electrolyte system, thus preventing parasitic reactions in damaging electrodes. DFT calculation proves that the 2-(N-morpholino)ethanesulfonic acid (MES) additive has strong affinity with Zn2+ and induces uniform deposition along (002) orientation. As a result, the Zn anode in MES-based electrolyte exhibits exceptional plating/stripping Zn||Zn lifespan. Secondly, a durable artificial ion-sieving layer made of MXene flakes (MXF), featuring numerous polar terminal groups, is developed to control the interfacial deposition behavior of Zn2+. In particular, the fragmented MXene flakes, produced by alkaline etching method, not only have strong Zn affinity to homogenize electric fields but also generate numerous zincophilic sites to reduce nucleation energy, thus securing a uniform dendrite-free surface during repeated stripping/plating process. Additionally, the porous and densely coated layer with polar groups allows the downward diffusion of Zn2+ to achieve bottom-up deposition and repels the excessive free water and anions to effectively prevent parasitic reactions. Therefore, the functional MXene flakes coated anode manifests a lower nucleation overpotential of 8.7 mV at 1.0 mA cm⁻² with 2700 h of stable plating/stripping in Zn||Zn cell. The ion-sieving effect of MXene flakes is firmly verified in cycling tests of the symmetric cells with an areal capacity of 10-40 mAh cm⁻² (1.0 mA cm⁻²) and 15-60% depth of discharge (DOD). Such a rational design of MXF protective layer breaks new ground in developing high plating capacity zinc anode for practical applications. Furthermore, MXene quantum dots (MQDs) are introduced as a multifunctional additive to build a robust solid electrolyte interphase (SEI) and a dynamic self-repairing interphase. Particularly, MQDs can effectively modify the H-bond environment, provide anti-corrosion benefits, and eliminate dendrites. The strong bonding of MQDs with free water molecules and metallic Zn enhances the electric double layer (EDL) and reconstructs the Helmholtz plane via modifying localized H-bond network. Depth profile analysis shows that Zn2+ plating coincides with SEI layer formation (ZHS/TiCO), resulting in uniform and dense deposition with mixed crystalline phases. Consequently, this additive strategy achieves dendrite-free deposition with a high Coulombic efficiency of 99.2%, a reversible lifetime of 3,700 hours in symmetric cells, anti-corrosion performance exceeding 4,000 hours, along with 3,900 hours of self-repairing cycling. Additionally, impressive full-cell cycling retention is further demonstrated with MnO₂, I₂, and PANI cathodes. This work paves the way for more efficient metallic anode in aqueous rechargeable batteries. Lastly, commercial glass fiber separators are hindered by zinc dendrite formation and low Coulombic efficiency, which compromise performance and safety. Cellulose-based separators have gained attention for their eco-friendliness, biodegradability, and cost-effectiveness. Notably, cellulose nanofibers (CNFs) offer strong anti-dendrite protection, but high production costs remain an issue. To address these, an all-cellulose membrane is introduced using affordable rice paper as the skeleton and CNFs as the functional material. This design significantly reduces costs while achieving excellent electrochemical performance, demonstrating impressive cycling stability and Coulombic efficiency. The all-cellulose membrane also provides superior mechanical strength and biodegradability, making it a promising candidate for sustainable battery applications. This work underscores the necessity of developing cost-effective, high-performance cellulose separators to advance ZIBs for practical and commercial use. |
| Rights: | All rights reserved |
| Access: | open access |
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