30 research outputs found
SENSING MECHANISM AND APPLICATION OF MECHANICAL STRAIN SENSOR: A MINI-REVIEW
This study reviews the potential of flexible strain sensors based on nanomaterials such as carbon nanotubes (CNTs), graphene, and metal nanowires (NWs). These nanomaterials have excellent flexibility, conductivity, and mechanical properties, which enable them to be integrated into clothing or attached to the skin for the real-time monitoring of various activities. However, the main challenge is balancing high stretchability and sensitivity. This paper explains the basic concept of strain sensors that can convert mechanical deformation into electrical signals. Moreover, this paper focuses on simple, flexible, and stretchable resistive and capacitive sensors. It also discusses the important factors in choosing materials and fabrication methods, emphasizing the crucial role of suitable polymers in high-performance strain sensing. This study reviews the fabrication processes, mechanisms, performance, and applications of stretchable strain sensors in detail. It analyzes key aspects, such as sensitivity, stretchability, linearity, response time, and durability. This review provides useful insights into the current status and prospects of stretchable strain sensors in wearable technology and human–machine interfaces
Effect of Mechanical Properties of Substrates on Flexibility of Ag Nanowire Electrodes under a Large Number of Bending Cycles
Ag nanowire electrodes have attracted considerable attention because of their potential applications in next-generation flexible electronics. However, there is a paucity of studies on the mechanical properties of Ag nanowire electrodes subjected to a large number of bending cycles. In this study, the effects of the substrate on the mechanical behavior of Ag nanowire electrodes were studied for a high bending frequency. The mechanical reliability of the Ag nanowire electrodes fabricated on a polyethylene terephthalate (PET) substrate was better than that for a polyimide (PI) substrate; the increase in the resistance of the PET-based Ag nanowire electrode was 1.07%, while that of the PI-based one was 1.23%. Nanoindentation tests showed that the elastic modulus of PI was larger than that of PET. This resulted in a lower bending strain on PET-based Ag nanowire electrodes compared to those on PI-based ones, because of the smaller distance from the neutral plane of the PET-based system. Our study showed that the mechanical properties of the substrate influenced the strain imposed on the thin layer on the substrates, which, in turn, determines the mechanical reliability of the thin-layer/substrate multilayer system
Polypyrrole–MnO<sub>2</sub>‑Coated Textile-Based Flexible-Stretchable Supercapacitor with High Electrochemical and Mechanical Reliability
Carbon-nanotube
(CNT)-based textile supercapacitors with MnO<sub>2</sub> nanoparticles
have excellent power and energy densities,
but MnO<sub>2</sub> nanoparticles can be delaminated during charge–discharge
cycles, which results in significant degradation in capacitance. In
this study, polypyrrole conductive polymer was coated on top of MnO<sub>2</sub> nanoparticles that are deposited on CNT textile supercapacitor
to prevent delamination of MnO<sub>2</sub> nanoparticles. An increase
of 38% in electrochemical energy capacity to 461 F/g was observed, while
cyclic reliability also improved, as 93.8% of energy capacity was
retained over 10 000 cycles. Energy density and power density
were measured to be 31.1 Wh/kg and 22.1 kW/kg, respectively. An in
situ electrochemical–mechanical study revealed that polypyrrole–MnO<sub>2</sub>-coated CNT textile supercapacitor can retain 98.5% of its
initial energy capacity upon application of 21% tensile strain and
showed no observable energy storage capacity change upon application
of 13% bending strain. After imposing cyclic bending of 750 000
cycles, the capacitance was retained to 96.3%. Therefore, the results
from this study confirmed for the first time that the polypyrrole–MnO<sub>2</sub>-coated CNT textile can reliably operate with high energy
and power densities with in situ application of both tensile and bending
strains
Highly Reliable Yarn-Type Supercapacitor Using Conductive Silk Yarns with Multilayered Active Materials
The fibrous supercapacitor is a promising candidate for wearable energy-storage systems due to excellent mechanical reliability under deformation. In this study, a mechanically reliable fibrous supercapacitor with high volumetric power density and energy density was developed using fiber electrodes composed of multilayered active materials coated on silk yarns. The conductive silk yarn electrodes are fabricated via a sequential dip-coating process of silver nanowires, multi-walled carbon nanotubes (MWCNT, three to seven walls), and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). The composite-coated silk yarn electrodes were stable under cyclic bending as well as under washing in water. Due to the synergetic effect of the three conducting materials, an excellent electrochemical performance was obtained resulting in high volumetric energy and power densities of 8–13 mWh cm−3 and 8–19\ua0W cm−3, respectively. A yarn-type supercapacitor was demonstrated by integrating composite-coated silk yarn electrodes with a hydrogel electrolyte, showing a promising stability as evidenced by the retention of over 94% and 93% of the specific capacitance after 90-degree bending and stretching
Three-Dimensional Nanofibrous Air Electrode Assembled With Carbon Nanotubes-Bridged Hollow Fe<sub>2</sub>O<sub>3</sub> Nanoparticles for High-Performance Lithium–Oxygen Batteries
Lithium–oxygen
batteries have been considered as one of the most viable energy source
options for electric vehicles due to their high energy density. However,
they are still faced with technical challenges, such as low round-trip
efficiency and short cycle life, which mainly originate from the cathode
part of the battery. In this work, we designed a three-dimensional
nanofibrous air electrode consisted of hierarchically structured carbon
nanotube-bridged hollow Fe<sub>2</sub>O<sub>3</sub> nanoparticles
(H-Fe<sub>2</sub>O<sub>3</sub>/CNT NFs). Composite nanofibers consisted
of hollow Fe<sub>2</sub>O<sub>3</sub> NPs anchored by multiple CNTs
offered enhanced catalytic sites (interconnected hollow Fe<sub>2</sub>O<sub>3</sub> NPs) and fast charge-transport highway (bridged CNTs)
for facile formation and decomposition of Li<sub>2</sub>O<sub>2</sub>, leading to outstanding cell performance: (1) Swagelok cell exhibited
highly reversible cycling characteristics for 250 cycles with a fixed
capacity of 1000 mAh g<sup>–1</sup> at a current density of
500 mA g<sup>–1</sup>. (2) A module composed of two pouch-type
cells stably powered an light-emitting diode lamp operated at 5.0
V