Fabrication and Electrochemical Characterization of Fiber-based Supercapacitors

Abstract

Supercapacitors (SCs) are suitable for energy storage of wearable devices because they are easy to fabricate using simple structure and flexible materials. It is possible to make SCs in the form of fibers or fabrics. Conventional fiber-type SCs (FSCs) have limited performance or complex and difficult processes to make them into fiber form. Therefore, it is necessary to develop a new structure of FSC. The bundles of fibers were spread and fixed, rolled up to form a fiber shape. The inside of FSC has a structure like a swiss roll, and the two electrodes are as close as possible to maintain a uniform distance. The distance between the electrodes affects the equivalent series resistance (ESR), which can improve the performance of the supercapacitor. Polyaniline (PANI) was synthesized on carbon fiber(CF) and used as the electrode. PVA/H2SO4 gel electrolyte was used to fabricate roll-type FSC. The fabricated roll-type FSC showed excellent durability and flexibility despite the complexity of the internal structure because it showed no performance deterioration even when it was bent to 30°. The performance of the roll-type FSC was compared with that of the conventional twist-type FSC and confirmed that it shows higher capacitance at the same current. The roll-type FSC showed lower ESR than the twist-type FSC. It was confirmed that the asymmetric roll-type FSC using PANI/CFs as the cathode and MoO3/CFs as the anode improved the performance by using a wider potential range. In order to apply an FSC directly to a garment, it needs to be fabricated as fabric. Conventional fabric-type SCs are fabricated in a sandwich form using two fabrics as electrodes. However, there is a disadvantage that the distance between the electrodes is long and the thickness of SC becomes thick due to two fabrics. To overcome these disadvantages and to maximize the performance of SCs, a new method for fabricating fabric-type SC was developed. Generally, the fabric is composed of warp and weft, and the SC consists of two electrodes, an electrolyte, and a separator. The warp and weft of the fabric are used as electrodes, respectively, a gel electrolyte acting as an electrolyte and a separator is used and the fabric itself could be used as a supercapacitor. Because it is a single fabric, the thickness is thin and the distance between the electrodes can be short. Symmetrical fabric-type SCs were fabricated using PANI/CFs and asymmetric fabric-type SCs were fabricated using MoO3/CFs as a cathode to confirm electrochemical performance. Also, it was confirmed that the performance was improved as the number of fibers per area of the fabric-type SC was controlled by adjusting the number of fibers and width entering the warp and weft. In the case of fabric-type SC, the larger the number of fibers per area, the more the effect of reducing the resistance of the SC itself due to the increase of the CFs as a collector, while the movement of the ions is impeded, and the electrochemical performance is improved because the ESR becomes smaller.