Flexible and wearable textile-based supercapacitors

Abstract

Nowadays, more and more attention has been drawn to the area of flexible and wearable electronics, which are found to have vast application possibilities such as in medical sensors or implants, portable military equipment and electronic textiles (E-textile) fields. Considering the exploitation of electronic technologies and the booming of the wearable electronic market, the development of wearable energy storage devices with the metrics of lightweight, flexibility, good safety level, and high energy/power performance is of great significance. Among them, textile-based electrochemical energy storages, particularly the textile-based supercapacitors (SCs), is one of the ideal candidates for wearable applications owing to their potentially excellent wearability and high integration feasibility. However, challenges remain in well balancing their electrochemical performances, mechanical properties and processing technologies. To address these challenges, this thesis focuses on developing the fully textile-based SCs through the utilization of textile materials, structures and processing technologies in the facile and continuous manners. Two major types of textile-based SCs, which were developed based on different commercial textile materials and facile fabrication techniques, are demonstrated. Firstly, metallic textiles were fabricated by means of polymer-assisted metal deposition (PAMD). By grafting the polymer brush and conducting the electroless metal deposition (ELD), Ni-coated cotton (Ni-Cotton) fabrics and yarns were obtained. These as-prepared Ni-Cotton textiles were highly electrically conductive, durable, and preserved textile-like flexibility. Subsequently, fabric-shaped SCs were developed based on Ni-Cotton fabrics. One-step direct electrospinning method was adopted to directly electrospin the carbon web with interconnected carbon nanofiber framework onto the Ni-Cotton fabric to form the composite electrode fabric. SC fabrics assembled with such fabric electrodes exhibited competitive electrochemical performance as well as good flexibility. They were also integrated into wearable form by simple sewing technology. Another type of SC fabric was directly assembled by yarn-shaped electrodes onto the arbitrary fabric substrate. Additive embroidery manufacturing (AEM) technique was developed for the fabrication of composite electrode yarns, the assembly and integration of device as well as its final encapsulation for wearing purpose. As proof of concept, SCs based on many kinds of electrode yarns were tailored on different fabric substrates. The as-made devices showed the reasonable capacitive performance and durability. Moreover, their washing ability was studied, showing the great application potential in the real scenarios of E-textiles. In summary, this work studied the feasibility of developing fully textile-based SCs from textile material, structural and processing technological points of view. Various types of flexible textile-based SCs have been successfully demonstrated. Such devices showed satisfactory electrochemical performance, excellent integration ability as well as potential wearability. This study opens a new avenue to incorporate traditional textile technologies and advanced material science for fabricating SC textiles with arbitrary architectures that are suitable for E-textile applications. In principle, fabrication and integration strategies reported in this research are also versatile to other electronic devices based on textile substrates. Therefore, the work presented here is expected to have significant impact on the fields of flexible and wearable electronics, and smart textiles and clothing.