Large-Scale, Lightweight, and Robust Nanocomposites Based on Ruthenium-Decorated Carbon Nanosheets for Deformable Electrochemical Capacitors.

Despite the increase in demand for deformable electrochemical capacitors as a power source for wearable electronics, significant obstacles remain in developing these capacitors, including their manufacturing complexity and insufficient deformability. With recognition of these challenges, a facile strategy is proposed to fabricate large-scale, lightweight, and mechanically robust composite electrodes composed of ruthenium nanoparticles embedded in freestanding carbon nanotube (CNT)-based nanosheets (Ru@a-CNTs). Surface-modified CNT sheets with hierarchical porous structures can behave as an ideal platform to accommodate a large number of uniformly distributed Ru nanoparticles (Ru/CNT weight ratio of 5:1) while improving compatibility with aqueous electrolytes. Accordingly, Ru@a-CNTs offer a large electrochemically active area, showing a high specific capacitance (∼253.3 F g-1) and stability for over 2000 cycles. More importantly, the exceptional performance and mechanical durability of quasi-solid-state capacitors assembled with Ru@a-CNTs and a PVA-H3PO4 hydrogel electrolyte are successfully demonstrated in that 94% of the initial capacitance is retained after 100 000 cycles of bending deformation and a commercial smartwatch is charged by multiple cells. The feasible large-scale production and potential applicability shown in this study provide a simple and highly effective design strategy for a wide range of energy storage applications from small- to large-scale wearable electronics.

Laser-Ablated Red Phosphorus on Carbon Nanotube Film for Accelerating Polysulfide Conversion toward High-Performance and Flexible Lithium-Sulfur Batteries.

The use of a conducting interlayer between separator and cathode is one of the most promising methods to trap lithium polysulfides (LiPSs) for enhancing the performance of lithium-sulfur (Li-S) batteries. Red phosphorus nanoparticles (RPEN )-coated carbon nanotube (CNT) film (RPEN @CF) is reported herein as a novel interlayer for Li-S batteries, which shows strong chemisorption of LiPSs, good flexibility, and excellent electric conductivity. A pulsed laser ablation method is engaged for the ultrafast production of RPEN of uniform morphology, which are deposited on the CNT film by a direct spinning method. The RPEN @CF interlayer provides pathways for effective Li+ and electron transfer and strong chemical interaction with LiPSs. The S/RPEN @CF electrode shows a superior specific capacity of 782.3 mAh g-1 (3 C-rate) and good cycling performances (769.5 mAh g-1 after 500 cycles at 1 C-rate). Density functional theory calculations reveal that the morphology and dispersibility of RPEN are crucial in enhancing Li+ and electron transfer kinetics and effective trap of LiPSs. This work demonstrates the possibility of using the RPEN @CF interlayer for the enhanced electrochemical performances of Li-S batteries and other flexible energy storage devices.

Flexible Thin Carbon Nanotube Web Film for Curved Heating Elements Under High Temperature Conditions.

Heating elements need a rapid heating property and long-term cycle stability when subjected to extreme temperatures. Carbon nanotube-based films can be used as ideal heating units owing to their superior electrical and thermal properties. However, carbon nanotube polymer composites are not appropriate for extreme conditions such as high temperatures (300 °C) due to the poor thermal stability of the polymer matrix. In this study, we fabricated a carbon nanotube web film, comprising heating elements consisting of pure carbon nanotubes, through the direct spinning method. The carbon nanotube web film has a microscale thickness. The carbon nanotube web film showed flexibility at high temperatures, while a fracture occurred in the case of the carbon nanotube polymer composite. We conducted electrical heating experiments on the curved carbon nanotube web film to observe the heating uniformity and flexibility. The heating test is conducted on various curved form heaters. The carbon nanotube web film showed rapid heating properties and a uniform heat distribution (temperature departure of less than 3%) without thermal aggregation. The curved heating units can be utilized in various applications such as functional clothes and de-icing systems having curved surfaces.

Effects of the aspect ratio of the conductive agent on the kinetic properties of lithium ion batteries.

We fabricated lithium-ion batteries (LIBs) using the Super P and carbon nanotubes (CNTs) as conductive agents to investigate the effect of the aspect ratio of conductive agent on the kinetic properties of LIB. The electrode fabricated with CNTs, which have a high aspect ratio (length: 200 µm), exhibited outstanding rate capability at 30C despite of their low concentration, while the electrode fabricated with the carbon black showed poor rate capability. These results indicate that the aspect ratio of conductive agent influence the diffusion coefficient of lithium ions, which is calculated from the galvanostatic intermittent titration technique analysis, and that conductive agent should have high aspect ratio to improve the kinetic properties of LIBs. This study provides insights that are useful for designing high-performance LIBs by reducing the amount of conductive agent, leading to increased loading of active material.

Carbon-Nanosheet Based Large-Area Electrochemical Capacitor that is Flexible, Foldable, Twistable, and Stretchable.

With the growing demand for wearable electronics, developing new compatible energy systems is a prominent topic of research. Energy systems mounted on wearable electronics should exhibit high cost efficiency, mechanical robustness, and high electrochemical activity. Herein, all-carbon-based large-area nanocomposites for freely deformable electrochemical capacitors are suggested to address these requirements. The three-dimensionally integrated, self-supported nanocomposites consist of activated carbons (ACs) distributed in direct spinning-derived carbon nanotube (DS-CNT) sheets without any additives, including conducting agents or binders. Owing to synergetic effects of the highly porous AC particles, high electron transport kinetics of CNTs, and facile ion accessibility resulting from acid treatment, the nanocomposites show a greatly improved specific capacitance of 128 F g-1 , compared to that of pristine ACs (62 F g-1 ), based on the total mass of the electrodes. The exceptional mechanical stability of the nanocomposites, which are attached on prestretched elastomer substrates, is confirmed; only a ≈15% increase in the electrical resistance is observed under a tensile strain of 100%, and the initial resistance is fully recovered after releasing. Finally, the outstanding durability and electrochemical performance of the deformable all-carbon-based symmetric capacitors under various mechanical deformations of bending, folding, twisting, and stretching are successfully demonstrated.