Abstract
Supercapacitor, also named as ultracapacitor or electrochemical capacitor, has emerged as a potential energy storage device to bridge the gap between the traditional capacitors and batteries, owing to its intrinsic characteristics, for instance, high power density and outstanding cycling stability. Recently, the fabrication of linear-shaped supercapacitors (e.g. wire- and fiber/yarn-shaped) has aroused increasingly more attention, because of their tiny volume, superior flexibility and outstanding capacitive performance, demonstrating great application potential in powering portable meanwhile wearable electronics that is an attractive research focus in energy storage. Moreover, it will be even more desirable to embed additional functionalities into these linear-shaped supercapacitors, and consequently exploiting their application area.Polypyrrole (PPy), one interesting conducting polymers, has its unique advantages over other contenders (e.g. metal oxides) when applied in supercapacitor as active material, such as environmental stability, high conductivity, good redox properties, and simple synthetic procedures. Higher electrochemical performance can be achieved by the introduction of nanostructured PPy and its nanocomposites into the supercapacitors. Thus, it is a splendid topic to fabricate high performance multi-functional linear-shaped supercapacitors based on PPy and its composites, meeting the requirements of practical application. In this thesis, two types of multi-functional linear-shaped supercapacitor have been attentively designed and successfully developed by using PPy and its composites as the loaded active materials: a self-healable prototype and a shape-memory prototype.
During their long life cycle, these linear supecapacitors unavoidably face the risks of accidental damages (e.g. tearing) when integrated in the wearable electronics, which seriously affects reliability of the whole device. So, it is with great realistic significance to embed mechanical and electrical self-healing properties in the linear supercapacitor, as an effective remedy for damaged device. Herein, a self-healable yarn-based supercapacitor that ensures the reconnection of the broken electrodes has been successfully developed by wrapping magnetic electrodes (PPy@Fe3O4) around a self-healing polymer shell (Polyurethane, PU). The strong force from magnetic attraction between the broken yarn electrodes benefits reconnection of fibers in the yarn electrodes during self-healing and thus offers an effective strategy for the restoration of electric conductivity, whereas the polymer shell recovers the configuration integrity and mechanical strength. With the brilliant design, the specific capacitance of prototype can be restored up to 71.8 % even after four breaking/healing cycles with great maintenance of the whole device’s mechanical properties.
As aforementioned, exceptionally long cycle life is one of the advantages of linear supercapacitor. During long-time practical application, these delicate devices unavoidably experience all kinds of repeated deformations (e.g. bending). These deformations would become irreversible under the long-term stress concentration, leading to structure and functional fatigue. A shape memory supercapacitor (SMSC) has been fabricated to solve this problem. The SMSC is flexible and easily deformed below its activation temperature. Once it is heated over the trigger temperature, it would automatically recover to original shape, meanwhile restoring all the deformations. By embedding with shape memory functions, all potential damages to the supercapacitor would be nipped in the bud, and simultaneously prolonging the life span of the device.
Even though high performance linear-shaped supercapacitors with multiple functions have been presented above, the fabrication process is obviously too complicated and far from satisfaction. Therefore, a novel modularization approach is also introduced in this thesis, which can realize fast assembling of multi-functional linear-shaped supercapacitors that saves materials and reduces workload in the same time. This facile approach is based on the usage of common module, a self-standing PPy-based tube, obtained from a reciprocal formwork construction technique. With the assistance of elastic solid electrolyte and flexible graphene, integrity of the inner PPy film in this common module will be perfectly retained even after detachment, which ensures outstanding performance of the resultant functional devices. By combining this common module with other building blocks, three kinds of linear prototypes are easily obtained, including shape memory supercapacitor, supercapacitor yarn and asymmetric supercapacitor, meeting the requirements of different applications.
In summary, different multi-funtional linear supercapactitors have been studied in depth in this thesis, aiming at obtaining high energy stroage capability together with improved damage management property. It is believed that the described strategies would inspire the ingenious designs of other multi-functional devices in the near future.
| Date of Award | 18 Aug 2016 |
|---|---|
| Original language | English |
| Awarding Institution |
|
| Supervisor | Chunyi ZHI (Supervisor) |