| Author: | Guo, Qianyi |
| Title: | High-performance flexible electrodes for lithium batteries |
| Advisors: | Zheng, Zijian (ABCT) |
| Degree: | Ph.D. |
| Year: | 2022 |
| Subject: | Lithium ion batteries -- Materials Electric batteries -- Electrodes Hong Kong Polytechnic University -- Dissertations |
| Department: | School of Fashion and Textiles |
| Pages: | xx, 127 pages : color illustrations |
| Language: | English |
| Abstract: | The urgent growing demand for flexible and portable electronic devices imposes a great necessity in the development of high-energy storage devices. The Lithium batteries are promising candidates to serve as power sources with flexibility, cost-effectiveness, and high energy density. Over decades, lithium-ion batteries (LIBs) have successfully commercialized and dominated the electronic and electric vehicle industries due to their stable cycling performance, lightweight and good safety. Nevertheless, the bottleneck of theoretical energy density (< 300 Wh kg-1) in LIBs urges the exploration of next-generation Li-based battery systems with higher energy density. Hence, Li-metal, lithium-sulfur batteries (LSBs), and dual-ion batteries (DIBs) have been developed. Despite various strategies that have been proposed, it remains a challenge for these batteries to achieve the milestone of > 500 Wh kg-1. To further enhance the high energy density, it's efficient to construct thick electrodes in these Li-based batteries to reduce the ratio of inactive materials at the cell level. However, it is hard for the thick electrodes to simultaneously achieve high mass loading, high performance, and good mechanical flexibility. Hence, we tried to construct a 3D thick electrode with good flexibility and easy tunability. Through special modification and adjustment of the fabrication processes, the designed electrodes can achieve flexibility, high loading, and high energy density in different Li-based cell systems. First, a freestanding carbon-based host compositing of carbon fibers (CF), carbon nanotube (CNT), and holey reduced graphene oxide (HrGO) was constructed. The self-assembled hosts (CF-CNT-HrGO) showed 3D interconnected skeleton with a hierarchical pore structure. With the unique lamellar 3D architecture, the as-fabricated ternary-phase host exhibited a polar surface with rich functional groups, large surface area, and good electric conductivity even upon repeated bending for 10000 cycles (resistance retention: ~100%). The as-obtained flexible composite could be applied as the thick hosts in diverse battery chemistries. For the LSBs, we designed a flexible 3D CF/sulfur covalently immobilized CNT/HrGO (CF-SKCNT-HrGO) cathode with both dissolution- and diffusion-limiting abilities for high performance in the thick loading condition. The functional groups in composite hosts provided surface covalent binding and chemical adsorption of sulfur species, enabling the electrodes with dissolution-limiting function. While the unique high-tortuosity design of ultrathick electrodes enabled it with polysulfide-blocking function. With these rational designs, the CF-SKCNT-HrGO processed an ultrahigh capacity of 13.0 mAh cm-2 (1444.3 mAh g-1), and a high energy density of 2888.6 Wh kg-1 and 1232.2 Wh L-1 at the high loading of 9.00 mg cm-2. For the LMBs, the CF-CNT-HrGO electrode could be acted as a high-loading hybrid Li-ion/Li-metal anode. With the Li-ion/Li-metal hybrid design, it could maintain the good stability of LIBs with additional energy capacity complemented by the Li metal. Upon the intercalation/deintercalation of Li ions, the thick CF-CNT-HrGO showed a largely improved specific capacity of 223.2 mAh gele-1 (13.39 mAh cm-2) even at a high loading of 60 mg cm-2. The energy density of whole cells could increase by 8% compared to that of conventional LFP||graphite batteries. During the plating/stripping of Li metal, the 3D hosts could homogenously deposit Li metal even at a high areal capacity of 12 mAh cm-2. The hybrid electrode could pair with the high-capacity LFP cathodes to achieve a stable and high capacity of 3.18 mAh cm-2 with a capacity retention of 99.91% per cycle. For the dual-ion batteries, the ternary-phase CF-CNT-HrGO cathode was demonstrated to process remarkably improved capacity and energy density. The combination of three types of carbon avoided the shortages of the individual components, for example, the low capacity of CF, the poor capacity stability of CNT, and the low conductivity of HrGO. Finally, the optimized ternary-phase cathode enabled a wide working window (1.5-5.0 V), a high reversible capacity and energy density (518.69 mAh g-1, 1191.46 Wh kg-1), good stability (373.01 mAh g-1 and 880.00 Wh kg-1 after 300 cycles). The unique electrode design addressed the main bottleneck of low energy density in DIBs. It is a significant step toward the practical application of the dual-ion battery system. In conclusion, we offered a promising and tailorable avenue to construct flexible and thick electrodes with superior performance, which solved the trade-off between mass loading and capacity. The as-developed electrode design was demonstrated to be available in diverse Li-based systems, including LSBs, LMBs, and DIBs. |
| Rights: | All rights reserved |
| Access: | open access |
Copyright Undertaking
As a bona fide Library user, I declare that:
- I will abide by the rules and legal ordinances governing copyright regarding the use of the Database.
- I will use the Database for the purpose of my research or private study only and not for circulation or further reproduction or any other purpose.
- I agree to indemnify and hold the University harmless from and against any loss, damage, cost, liability or expenses arising from copyright infringement or unauthorized usage.
By downloading any item(s) listed above, you acknowledge that you have read and understood the copyright undertaking as stated above, and agree to be bound by all of its terms.
Please use this identifier to cite or link to this item:
https://theses.lib.polyu.edu.hk/handle/200/12174