Coaxial wet-spun yarn supercapacitors for high-energy density and safe wearable electronics

Abstract

Yarn supercapacitors have great potential in future portable and wearable electronics because of their tiny volume, flexibility and weavability. However, low-energy density limits their development in the area of wearable high-energy density devices. How to enhance their energy densities while retaining their high-power densities is a critical challenge for yarn supercapacitor development. Here we propose a coaxial wet-spinning assembly approach to continuously spin polyelectrolyte-wrapped graphene/carbon nanotube core-sheath fibres, which are used directly as safe electrodes to assembly two-ply yarn supercapacitors. The yarn supercapacitors using liquid and solid electrolytes show ultra-high capacitances of 269 and 177 mF cm−2 and energy densities of 5.91 and 3.84 μWh cm−2, respectively. A cloth supercapacitor superior to commercial capacitor is further interwoven from two individual 40-cm-long coaxial fibres. The combination of scalable coaxial wet-spinning technology and excellent performance of yarn supercapacitors paves the way to wearable and safe electronics.

A General Electrode Design Strategy for Flexible Fiber Micro‐Pseudocapacitors Combining Ultrahigh Energy and Power Delivery

“…The specific areal capacitance of our solid‐state fiber device with PVA/KOH electrolyte at 0.41 mA cm −2 is ≈2–350 times of previously reported solid‐state fiber SCs measured at much lower rates (typically 0.01–0.1 mA cm −2 ) reported so far (see Table S1, Supporting Information) 1, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36. More importantly, both the areal energy and power densities of 18.83 µWh cm −2 and 16.33 mW cm −2 based on the device (75.32 µWh cm −2 and 65.32 mW cm −2 based on one electrode) are substantially higher than those of previous advanced fiber devices using hollow rGO/PEDOT: PSS fiber (6.8 µWh cm −2 , 0.166 mW cm −2 ),30 rGO/MnO 2 /PPy@metal yarn (9.2 µWh cm −2 , 1.5 mW cm −2 ),31 MnO 2 /CNT fiber (8.5 µWh cm −2 ),20 PPy@CNTs@urethane elastic fibers (6.13 µWh cm −2 , 0.133 mW cm −2 ),26 GO/CNT@carboxymethyl cellulose fibers (3.84 µWh cm −2 , 0.19 mW cm −2 ),5 and nanoporous Au wire@MnO 2 //CNT/carbon fibers (5.4 µWh cm −2 , 2.53 mW cm −2 ) 36. To our knowledge, the areal energy and power densities for our prototype device represent the highest values among all solid‐state symmetric fiber SCs (Table S1, Supporting Information).…”

“…However, the major bottleneck for the existing fiber m‐SCs lies in their much lower areal energy density relative to routine planar SCs8 or batteries 2. In this context, considerable efforts were concentrated on exploring proper fiber electrode materials with large capacitance for improving the energy density, while maintaining high power density 1, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17. Various carbonaceous materials like activated carbon,9, 10 carbon nanotubes (CNTs),11, 12, 13 reduced graphene oxide (rGO),14, 15, 16 and our recently developed rGO/CNT hybrids17, 18 were exploited as active materials for fiber m‐SCs, yet their applications are restricted by the low capacitance of <200 mF cm −2 .…”

“…As expected, the CV curves for the constructed fiber SC at various scanning rates (5–100 mV s −1 ) present a nearly rectangular shape in the potential window of 0–0.8 V (Figure S7, Supporting Information), while the GCD curves as a function of the applied current densities ( Figure 4 a) have a triangular‐like shape with a small IR‐drop voltage, suggesting good reversibility and charge propagation in the fiber‐like format. Despite the fact that the solid‐state electrolytes have poorer ion diffusivity relative to the liquid electrolyte, the MnO 2 /porous Ni wire electrode still yields a remarkable specific areal capacitance as high as 847.22 mF cm −2 at 0.41 mA cm −2 with the corresponding length capacitance of 79.81 mF cm −1 , which is substantially higher than those of previous MnO 2 ‐based fiber electrodes such as MnO 2 /rGO fibers (9.6 mF cm −2 ),24 MnO 2 /CNT yarn (61.25 mF cm −2 ),21 polypyrrole(PPy)/MnO 2 /rGO/metal yarns (411 mF cm −2 at 0.092 mA cm −2 ),31 and other representative high‐performance fiber electrodes measured at much lower current densities (0.01–0.1 mA cm −2 ) such as hollow rGO/poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS) fibers (304.5 mF cm −2 at 0.08 mA cm −2 ),30 CNT/Co 3 O 4 fibers (52.6 mF cm −2 at 0.053 mA cm −2 ),23 CNT/polyaniline fibers (38 mF cm −2 at 0.01 mA cm −2 ),27 CNT/activated carbon yarns (31.7 mF cm −2 at 0.05 mA cm −2 ),13 and rGO/CNT@ carboxymethyl cellulose fibers (177 mF cm −2 at 0.1 mA cm −2 ),5 and even superior to some MnO 2 ‐based macroscopic SCs using MnO 2 /nickel wire arrays/Ti foil (750 mF cm −2 ) and MnO 2 /nickel foam (557 mF cm −2 ) 41, 42. More significantly, our fiber device can operate even at a very high current density up to 16.33 mA cm −2 .…”

“…To our knowledge, the areal energy and power densities for our prototype device represent the highest values among all solid‐state symmetric fiber SCs (Table S1, Supporting Information). 1, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36 …”

Fiber‐Type Solar Cells, Nanogenerators, Batteries, and Supercapacitors for Wearable Applications

“…Typically used active materials are carbon nanoparticles, metal oxides, and conducting polymers 144, 149, 150, 151. Several device architectures have been developed for yarn supercapacitor, such as biscrolled or two‐ply yarn, multi‐ply yarn, braided, core–shell, and coaxial yarns 134, 152, 153, 154, 155, 156…”