Cotton yarns modified with three-dimensional metallic Ni conductive network and pseudocapacitive Co-Ni layered double hydroxide nanosheet array as electrode materials for flexible yarn supercapacitors

Tip effect of NiCo-LDH with low crystallinity for enhanced energy storage performance of yarn-shaped supercapacitors

Layered double hydroxides (LDHs) are considered promising materials for supercapacitor applications. However, the development of yarn-shaped supercapacitors (YSCs) with high electrochemical performance utilizing LDHs remains challenging. In this study, the NiCo-LDHs with various morphologies (nano-needles, nano-sheets, needle-sheet composites, and nano-flowers) were grown on carbon nanotubes (CNTs)-functionalized cotton yarn via a co-precipitation technique for YSC applications. Among these, the yarn incorporating nano-needle NiCo-LDHs exhibited reduced crystallinity yet demonstrated a superior areal capacitance compared to other morphologies, following a diffusion-controlled process. Finite element simulations were subsequently conducted to investigate this phenomenon, revealing that the lower-crystallinity nano-needle NiCo-LDHs accumulated a greater charge at their tips, thereby enhancing redox reactions and achieving higher energy storage capacitance. Subsequently, the yarns with nano-needle NiCo-LDHs were assembled into flexible quasi-solid-state symmetric YSCs, achieving a peak areal capacitance of 124.27 mF cm-2 and an exceptionally high energy density of 39.4 μWh cm-2 at a current density of 0.2 mA cm-2. Furthermore, our YSCs can be scaled up through serial or parallel connections and integrated into fabrics, making them suitable for wearable energy storage applications. This work provides an efficient method for fabricating high-performance YSCs and demonstrates significant potential for wearable energy storage devices.

Core-shell heterostructured Ni(OH)2@activation Zn-Co-Ni layered double hydroxides electrode for flexible all-solid-state coaxial fiber-shaped asymmetric supercapacitors

The increasing requirements for wearable and portable electronics are driving the interests of high performance fiber supercapacitor. Layered double hydroxide (LDH) is broadly used in electrode materials, owing to the adjustability of components and the unique lamellar structure. However, limited active sites and poor electrical conductivity hinder its applications. Herein, the core-shell heterostructured Ni(OH)2@activation Zn-Co-Ni layered double hydroxides (Ni(OH)2@A-ZnCoNi-LDH) electrode was fabricated by loading pseudocapacitance material on the A-ZnCoNi-LDH to improve the electrochemical performance. Significantly, benefits from the synergistic effect of the multi-metal ions and the core-shell heterostructure, the electrodes demonstrated a capacitance of 2405 mF·cm-2 at 1 mA·cm-2. Furthermore, Ni(OH)2@A-ZnCoNi-LDH was used as the core electrode and carbon nanotube (CNT) film coated with Fe2O3@reduced graphene oxide (rGO) was wrapped around the core electrode to assemble coaxial fiber asymmetric supercapacitor, which illustrated an ultrahigh energy density of 177.7 µWh·cm-2 at 0.75 mW·cm-2. In particular, after consecutive charging and discharging 7000 cycles, the capacitance retention of the device was 95 %, indicating the excellent cycling stability. Furthermore, the device with high flexibility can be woven into textiles in different shapes. The fabricated device has an excellent development prospect as an energy source in wearable electronic devices.

Smart Electronic Textile-Based Wearable Supercapacitors

Electronic textiles (e-textiles) have drawn significant attention from the scientific and engineering community as lightweight and comfortable next-generation wearable devices due to their ability to interface with the human body, and continuously monitor, collect, and communicate various physiological parameters. However, one of the major challenges for the commercialization and further growth of e-textiles is the lack of compatible power supply units. Thin and flexible supercapacitors (SCs), among various energy storage systems, are gaining consideration due to their salient features including excellent lifetime, lightweight, and high-power density. Textile-based SCs are thus an exciting energy storage solution to power smart gadgets integrated into clothing. Here, materials, fabrications, and characterization strategies for textile-based SCs are reviewed. The recent progress of textile-based SCs is then summarized in terms of their electrochemical performances, followed by the discussion on key parameters for their wearable electronics applications, including washability, flexibility, and scalability. Finally, the perspectives on their research and technological prospects to facilitate an essential step towards moving from laboratory-based flexible and wearable SCs to industrial-scale mass production are presented.

Surface Modification of Commercial Cotton Yarn as Electrode for Construction of Flexible Fiber-Shaped Supercapacitor

In this study, we report on the rational design and facile preparation of a cotton-reduced graphene oxide-silver nanoparticle (cotton-RGO-AgNP) hybrid fiber as an electrode for the building of a flexible fiber-shaped supercapacitor (FSSC). It was adequately characterized and found to possess a well-defined core−shell structure with cotton yarn as a core and a porous RGO-AgNP coating as a shell. Thanks to the unique morphological features and low electrical resistance (only 2.3 Ω·cm−1), it displayed attractive supercapacitive properties. When evaluated in a three-electrode setup, this FSSC electrode delivered the highest linear and volumetric specific capacitance of up to ca. 12.09 mF·cm−1 and ca. 9.67 F·cm−3 with a satisfactory rate capability as well as a decent cycling stability. On the other hand, an individual parallel symmetric FSSC cell constructed by this composite fiber fulfilled the largest linear and volumetric specific capacitance of ca. 1.67 mF·cm−1 and ca. 0.67 F·cm−3 and offered the maximum energy density, as high as ca. 93.1 μWh·cm−3, which outperformed a great number of graphene- and textile yarn-based FSSCs. Impressively, bending deformation brought about quite a limited effect on its electrochemical behaviors and almost no capacitance degradation took place during the consecutive charge/discharge test for over 10,000 cycles. Consequently, these remarkable performances suggest that the currently developed cotton-RGO-AgNP fiber has considerable application potential in flexible, portable and wearable electronics.

Superior performance of flexible solid-state supercapacitors enabled by ultrafine graphene quantum dot-decorated porous carbon spheres

Graphene quantum dot-decorated porous carbon spheres were synthesized via a facile and green route in this study.

Nanoneedle-decorated NiCo-layered double hydroxide microspheres tuned as high-efficiency electrodes for pseudocapacitors

Nanoneedle-decorated flower-like NiCo-LDH microspheres are tuned by varying the amounts of NH₄F, providing tunable electrochemical performance for their use as electrodes for pseudocapacitors.