| dc.description.abstract | Supercapacitors (SCs) as a new class of energy storage devices have attracted great attention in industry and academia community due to their higher energy density than dielectric capacitors, higher power density than rechargeable batteries, long cycle life, safety and environment friendliness. Although they have many attractive advantages and much work has been done to improve their performance, their relatively low energy density compared with batteries has severely limited their practical applications to some extent. At the same time, the rapid development of micro-electromechanical systems (MEMS), portable/wearable electronic devices, and self-powered systems have stimulated new demands for SCs with small size, various shapes, lightweight, flexibility as well as compatibility. However, the current development of SCs with large size, heavy weight and rigid nature clearly lags behind these new requirements. To address these issues, it is highly desired to develop new-concept SCs by innovating upon their design from various aspects (e.g., electrode materials, electrode configuration, and preparation technology), thus matching these new demands and endowing the obtained SCs with real applications.
Based on the above considerations, my thesis mainly focuses on the development of new-concept SCs by exploring alternative electrode materials with unique structure and texture, introducing new energy storage mechanism, and designing new electrode configuration to overcome the abovementioned limitations and meet these new requirements:
(1) To increase the energy density of SCs, lithium ion hybrid supercapacitors (LIHSs) as a new-concept energy storage system have been constructed by consisting of a battery-type anode (3D graphene-wrapped MoO3 nanobelts foam) and a capacitor-type cathode (3D graphene-wrapped polyaniline nanotube derived carbon). From the viewpoint of material design, it is expected to effectively take the advantage of each component and synergistic effect to endow the resulting materials with excellent electrochemical performance. Encouragingly, benefiting from these unique structures and configuration, the obtained LIHSs exhibit large operating voltage (up to 3.8 V), high energy and power densities, and long cycling stability.
(2) To match these emerging portable/wearable electronic devices, a flexible fiber-shaped micro-supercapacitor (MSC) has been rationally designed and successfully prepared with coaxial human hair/Ni/graphene/MnO2 fiber as positive electrode and coaxial human hair/Ni/graphene fiber as negative electrode. With the facile fabrication technique (e.g., self-assembly, chemical bath) and the unique morphology and structure of electrode materials as well as the asymmetrical configuration, the as-prepared MSCs display extraordinary flexibility and outstanding electrochemical performance including a wide potential window, an excellent rate capability, a fast frequency response (τ0 = 55 ms), a high volumetric energy density, and a long cycle life.
(3) In the last section, the surface and structural engineering strategies by downsizing to quantum dot scale, doping heteroatoms, creating more defects, and introducing more rich functional groups are employed to tailor the physicochemical properties of 2D materials (e.g., graphene, MoS2), thereby boosting the electrochemical performance of in-plane MSCs. Notably, the resulting nitrogen-doped graphene quantum dots (N-GQDs) and molybdenum disulfide quantum dots (MoS2-QDs) show outstanding electrochemical performance as negative and positive electrode materials, respectively. Importantly, the obtained N-GQDs//MoS2-QDs asymmetric in-plane MSCs exhibit a large operating voltage up to 1.5 V (far exceeding that of most reported MSCs), an ultrafast frequency response (with a short time constant of 0.087 ms), a high energy density, and a long-term stability. | en |
