Miniaturized Stretchable and High-Rate Linear Supercapacitors

A Review of Yarn-Based One-Dimensional Supercapacitors

Energy storage in a one-dimensional format is increasingly vital for the functionality of wearable technologies and is garnering attention from various sectors, such as smart apparel, the Internet of Things, e-vehicles, and robotics. Yarn-based supercapacitors are a particularly compelling solution for wearable energy reserves owing to their high power densities and adaptability to the human form. Furthermore, these supercapacitors can be seamlessly integrated into textile fabrics for practical utility across various types of clothing. The present review highlights the most recent innovations and research directions related to yarn-based supercapacitors. Initially, we explore different types of electrodes and active materials, ranging from carbon-based nanomaterials to metal oxides and conductive polymers, that are being used to optimize electrochemical capacitance. Subsequently, we survey different methodologies for loading these active materials onto yarn electrodes and summarize innovations in stretchable yarn designs, such as coiling and buckling. Finally, we outline a few pressing research challenges and future research directions in this field.

Highly Stretchable and Strain-Insensitive Fiber-Based Wearable Electrochemical Biosensor to Monitor Glucose in the Sweat

Development of high-performance fiber-shaped wearable sensors is of great significance for next-generation smart textiles for real-time and out-of-clinic health monitoring. The previous focus has been mainly on monitoring physical parameters such as pressure and strains associated with human activities. Development of an enzyme-based non-invasive wearable electrochemical sensor to monitor biochemical vital signs of health such as the glucose level in sweat has attracted increasing attention recently, due to the unmet clinical needs for the diabetic patients. To achieve this, the key challenge lies in the design of a highly stretchable fiber with high conductivity, facile enzyme immobilization, and strain-insensitive properties. Herein, we demonstrate an elastic gold fiber-based three-electrode electrochemical platform that can meet the aforementioned criteria toward wearable textile glucose biosensing. The gold fiber could be functionalized with Prussian blue and glucose oxidase to obtain the working electrode and modified by Ag/AgCl to serve as the reference electrode; and the nonmodified gold fiber could serve as the counter electrode. The as-fabricated textile glucose biosensors achieved a linear range of 0-500 μM and a sensitivity of 11.7 μA mM^-1 cm^-2. Importantly, such sensing performance could be maintained even under a large strain of 200%, indicating the potential applications in real-world wearable biochemical diagnostics from human sweat.

A self-healing conductive and stretchable aligned carbon nanotube/hydrogel composite with a sandwich structure

Self-healing conductive elastomers have emerged as a class of novel materials that are important for fabricating human-motion sensors, soft robots and healthcare monitoring systems. Herein, we report on a hydrogel of modified poly(γ-glutamic) acid polymer chains crosslinked by coordination complexes, which exhibits good stretchability (1375%), long-term stability (more than 40 days), and self-healing ability (99.0 ± 1.5% in 3 h). Furthermore, a "sandwich" structure composite was fabricated, which is composed of self-healing hydrogels and Au nanograin-decorated aligned multiwall carbon nanotube sheets. It possesses fast self-healing ability, a low stable electronic resistance of 10 ± 1 Ω sq^-1, in the temperature range of -40-90 °C, the humidity range of 10-90%, and a stretching range up to 200%.

Modified Carbon Fiber Paper-Based Electrodes Wrapped by Conducting Polymers with Enhanced Electrochemical Performance for Supercapacitors

An easy approach to fabricating carbon fiber paper (CFP) based electrodes has been developed. This method can be mainly divided into two steps, for which the mixture of cellulose nanofibers (CNFs) and carbon nanotubes (CNTs) was first deposited on the surface of carbon fiber paper through a vacuum filtration device followed by immersing the hybrid paper into concentrated aniline solution to polymerize polyaniline (PANI). Compared to carbon fiber paper, the acid-treated carbon fiber paper (A-CFP)-based electrode provides more active sites, which are beneficial for the polymerization of polyaniline. The mixture of CNFs and CNTs could coat on the A-CFP by vacuum-filtration due to the high hydrophilicity of A-CFP improved by acid-treatment. PANI with different polymerization time was in-situ synthesized on the surface of the hybrid paper to form a three-dimensional cross-linked structure that greatly enhanced the electrochemical performance of the electrode by improving high capacitance, high rate-capability, and long cycle-life. Moreover, the assembled symmetrical supercapacitor showed a high area capacitance of 626 mF·cm^-2 and an energy density of 87 µWh·cm^-2. This facile, easy performed, and low-cost strategy may provide a feasible method for the production of supercapacitor electrodes.