Wearable energy-dense and power-dense supercapacitor yarns enabled by scalable graphene–metallic textile composite electrodes

Abstract

One-dimensional flexible supercapacitor yarns are of considerable interest for future wearable electronics. The bottleneck in this field is how to develop devices of high energy and power density, by using economically viable materials and scalable fabrication technologies. Here we report a hierarchical graphene–metallic textile composite electrode concept to address this challenge. The hierarchical composite electrodes consist of low-cost graphene sheets immobilized on the surface of Ni-coated cotton yarns, which are fabricated by highly scalable electroless deposition of Ni and electrochemical deposition of graphene on commercial cotton yarns. Remarkably, the volumetric energy density and power density of the all solid-state supercapacitor yarn made of one pair of these composite electrodes are 6.1 mWh cm−3 and 1,400 mW cm−3, respectively. In addition, this SC yarn is lightweight, highly flexible, strong, durable in life cycle and bending fatigue tests, and integratable into various wearable electronic devices.

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.…”

“…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 .…”

“…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 . Alternatively, incorporating pseudocapacitive materials into fiber m‐SCs is a superior solution to achieve high‐density energy due to 10–100 times higher theoretical capacitance than carbon materials 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36.…”

“…As compared, metallic scaffold was recognized as the best candidate for long‐range electron transport 31, 32, 33, 34, 35, 36. For instances, bare Ni wires were often utilized as conductive skeletons to load various active materials like Ni(OH) 2 /rGO,[[qv: 36b]] CuCo 2 O 4 nanowires,[[qv: 36c]] and rGO15 for fiber m‐SCs. However, these bare metallic wires are solid and often suffer from limited surface area,31, 32, 33, 34, 35, 36 also commonly seen in carbon‐based fiber electrodes 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30.…”

Microfluidic Patterning of Metal Structures for Flexible Conductors by In Situ Polymer‐Assisted Electroless Deposition

“…More recently, several advances in polymer‐assisted ELD16, 17, 18 have been accomplished for the fabrication of highly conductive metal structures for flexible and stretchable interconnects,19, 20, 21, 22 supercapacitors,23, 24 conductive textiles,25, 26 and optoelectronic devices 27, 28. The polymer‐assisted ELD typically involves three major steps: surface modification of functional polymer anchoring layers, loading of catalyst moieties to the polymer anchoring layer by ion exchange, and site‐selective metal electroless deposition.…”