Carbon based self-supported electrodes for supercapacitors and batteries

• Main Author: Wang, Huanhuan
• Other Authors: Shen Zexiang
• Format: Theses and Dissertations
• Language: English
• Published: 2019
• Subjects: DRNTU::Engineering::Materials
• Online Access: https://hdl.handle.net/10356/104893; http://hdl.handle.net/10220/47832
• Institution: Nanyang Technological University

Electrochemical energy storage devices based on conducting polymers deliver higher specific capacity compared with carbon-based supercapacitors and superior kinetics compared to metal-based batteries, thus bridging the gap between capacitors and batteries. Polyaniline as a typical conducting polymer exhibits high pseudocapacitance in supercapacitors. In chapter 4, the binder-free supercapacitor electrodes of PANi and carbon black with high specific capacity and fully reversible feature are successfully synthesized via a one-step potentialdynamic co-deposition method. Significant effect of carbon black has been demonstrated, i.e., it plays an important role in producing high conductivity, porous and extended conformation structure with high oxidation state and depressed hydrolysis effect, leading to superior capacitive performance. This promotes better understanding about synergistic effect between different components in hybrid electrode materials and opens up new research in the following. In chapter 5, much efforts have been made on nanoscale engineering in designing novel self-supported electrode based on tin sulfide and PANi network. The combination of tin sulfide and polyaniline evokes synergistic effect to enhance the performance. On one hand, the polyaniline nanofibers facilitate the growth of tin sulfide flakes in nanosize, which is helpful for improving the capacity and stability of the electrode. On the other hand, unlike carbon additives, tin sulfide nanoflakes exhibit high capacity due to greatly decreased particle size and introduced mesopores, nanoclusters, and exposed edges. Benefiting from effective nanostructure engineering, good electrochemical performance has been demonstrated and a Na+ intercalation mechanism is unraveled. This is the first time that tin sulfide-based material is fabricated as a self-supported electrode for supercapacitors. Supercapacitors and batteries have been playing great roles in different energy supply demands due to different electrochemical features. Besides the morphological and structural design via nanoscale engineering, the fundamental studies are equally important to improve electrochemical performance of these energy storage devices. In chapter 6, the morphology/components and growth mechanism of solid electrolyte interface on carbon-based anode is investigated in KPF6 and KN(SO2F)2 (KFSI)-based organic electrolytes, aiming to unravel the SEI effect on K+ ion storage mechanism. Electrochemical characterizations disclose that the KFSI-based cells deliver improved electrochemical performance in terms of coulombic efficiency and cycling stability, compared to KPF6-based cells. Experimental results including depth-profiling XPS study, ex-situ TEM, SEM, and FTIR analysis, reveal that KFSI salt contributing to a thin, uniform and smooth SEI layer compared to KPF6 induced SEI layer, ensuring good cycling stability and high reversibility. Based on the optimized electrolyte in chapter 6, the nitrogen doping effect on K+ storage in graphite is explored. It is found that i) the induced holey active sites provide more sites for K+ storage, ii) the enlarged interlayer spacing facilitates K+ intercalation, and iii) the improved electronic conductivity ensures fast kinetics. All these features together, lead to superior electrochemical performance. Furthermore, the K+ storage behavior is strongly dependent on the both nitrogen concentrations and types. Specifically, the pyridinic/pyrrolic nitrogen doping is helpful in creating holey structures via high doping intensities to accommodate more K+. These results promote better understanding of K+ ion storage mechanism and provide guidance for optimized carbon-based electrode design.