Full metadata record
| DC Field | Value | Language |
|---|---|---|
| dc.contributor | School of Fashion and Textiles | en_US |
| dc.contributor.advisor | Zheng, Zijian (SFT) | en_US |
| dc.creator | Yu, Wancheng | - |
| dc.identifier.uri | https://theses.lib.polyu.edu.hk/handle/200/14517 | - |
| dc.language | English | en_US |
| dc.publisher | Hong Kong Polytechnic University | en_US |
| dc.rights | All rights reserved | en_US |
| dc.title | Energy-dense flexible li-ion batteries based on ultralight metal-coated fabrics | en_US |
| dcterms.abstract | Li-ion batteries (LIBs) are the most essential energy storage devices in daily life because of their advantages of high energy density, no memory effect and mature production techniques. Besides increasing energy density, rendering the LIBs with high flexibility has become another critical research topic to power flexible or wearable electronics. Hundreds of works have been proposed to realize flexible lithium batteries (FLBs), and these methods can be simply classified into two major strategies: soft structure and soft materials. Structure design can protect the rigid parts of LIBs by controlling the distribution of stress, however, getting flexibility usually leads to lower energy density because of the introduction of inactive components or inferior electrochemical performance. Although using carbonaceous materials such as carbon nanotubes (CNTs) and graphene as current collectors can essentially improve the deformability of the battery, their preparations are complex and expensive. Hence, it is necessary to develop new kinds of current collectors that manifest comprehensive properties combined with low cost, low areal density, high conductivity, excellent flexibility, and outstanding electrochemical stability, to manufacture highly flexible and energy-dense FLBs. | en_US |
| dcterms.abstract | First, the polymer-assisted metal deposition (PAMD) method is adopted for wrapping metal layers (Cu and Ni) on thin glass-fiber fabrics (GFs). GFs are widely used as insulating material because of their high strength, deformability, and chemical stability. The polymer interlayer facilitates a more stable interfacial adhesion between the metal layer and GFs. As a result, metal-coated GFs (MGFs) exhibit qualified electrical conductivity and excellent mechanical durability. With much lower areal densities (2.9-3.2 mg cm⁻²) than Cu foil (7.5 mg cm⁻²) and Al foil (4.2 mg cm⁻²), the FLBs using MGFs show improvements of 9~18% on the energy density. In addition, the MGF-based pouch cell shows a high capacity retention of 94.1% after 500 bending cycles at radius of 5 mm and another 500 bending cycles at 2 mm. | en_US |
| dcterms.abstract | Then, a flexible and high-voltage current collector was fabricated by the modified electroless deposition (ELD) method. It was found that the working potential range of Ni-coated GF (NiGF) is just up to 4 V vs. Li/Li⁺, which can only support the lithium iron phosphate (LFP), a low-energy cathode material. Hence, Ni coating is replaced with the Ni/P composite to increase the anodic stability of the cathode current collector. The resultant Ni/P composite-coated GF (NiPGF) is proved to be a qualified high-voltage current collector with an onset anodic potential of ~4.7 V. Also, NiPGF-based electrodes display similar electrochemical performances to Al-based electrodes with lower areal density and much better flexibility. The atomic layer deposition (ALD) method protects the P from dissolution, resulting in a reasonable cyclic performance for the full cell using NiPGF. Dynamic bending test indicates the stable power output of the NiPGF-based pouch cell under a low bending radius of 5 mm. | en_US |
| dcterms.abstract | At last, the polymer fabrics substrate with lower areal density and better mechanical properties is applied to further increase the energy density and flexibility of the FLB. Unlike glass fiber, polyethylene terephthalate (PET) is soft in nature, which makes the resultant fabrics more resilient. However, PET is not as inertial as GFs so the side reactions become an urgent issue to be addressed. The degradation mechanism is clarified by the careful characterizations of the Fourier transform infrared spectroscopy (FTIR) and the morphology change of Cu-coated PET fabrics (CuPET) during the ELD process. After the additional electroplating of Cu, the PET substrate is fully covered and separated from the electrolyte. A high energy density of 207 Wh kg⁻¹ is achieved for the full cell using metal-coated PET fabrics (MPETs), which is 17% higher than that of the full cell using metal foils. By inheriting the excellent mechanical flexibility of PET fabrics, the pouch cell shows high capacity retention of ~80% after the bending test that 500 bending cycles for each bending radius (5 mm, 2mm and 1 mm) was conducted. In a rigorous and continuous bending process of 3 mm, the pouch cell maintains ~87% discharging capacity compared to the flat state. | en_US |
| dcterms.abstract | In summary, we propose a series of flexible, superlight, highly conductive, and electrochemically stable fabric-based current collectors. Compared to commercially used Cu and Al foils, they display much lower areal density and better deformability. It means that we can improve the energy density and flexibility of the FLB, simultaneously, by using fabric-based current collectors. The transplantable preparation and protection methods in this thesis pave the way for manufacturing textile-based current collectors for future large production of FLBs. | en_US |
| dcterms.extent | xxi, 180 pages : color illustrations | en_US |
| dcterms.isPartOf | PolyU Electronic Theses | en_US |
| dcterms.issued | 2024 | en_US |
| dcterms.educationalLevel | Ph.D. | en_US |
| dcterms.educationalLevel | All Doctorate | en_US |
| dcterms.accessRights | open access | en_US |
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