Air-Stable, High-Performance, Flexible Microsupercapacitor with Patterned Ionogel Electrolyte

We describe the fabrication of air-stable, high-performance, planar microsupercapacitors (MSCs) on a flexible poly­(ethylene terephthalate) substrate with patterned ionogel electrolyte, i.e., poly­(ethylene glycol) diacrylate/1-ethyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide, and electrodes of spray-coated multiwalled carbon nanotubes. The flexible MSC showed good cyclability, retaining ∼80% of initial capacitance after 30 000 cycles, and good mechanical stability down to a bending diameter of 3 mm under compressive stress; 95% of the initial capacitance was retained after 1000 bending cycles. The MSC had high electrochemical stability with retaining 90% of its initial capacitance for 8 weeks in air. Furthermore, vertical stacking of MSCs with patterned solid film of ionogel electrolyte could increase the areal capacitance dramatically. This flexible MSC has potential applications as an energy-storage device in micro/nanoelectronics, without encapsulation for air stability

Wire-Shaped Supercapacitors with Organic Electrolytes Fabricated via Layer-by-Layer Assembly

A wire-shaped supercapacitor (WSS) has structural advantages of high flexibility and ease of incorporation into conventional textile substrates. In this work, we report a thin reproducible WSS fabricated via layer-by-layer (LbL) assembly of multiwalled carbon nanotubes (MWCNTs), combined with an organic electrolyte of propylene carbonate (PC)–acetonitrile (ACN)–lithium perchlorate (LiClO₄)–poly­(methyl methacrylate) (PMMA) that extends the voltage window to 1.6 V. The MWCNTs were uniformly deposited on a curved surface of a thin Au wire using an LbL assembly technique, resulting in linearly increased areal capacitance of the fabricated WSS. Vanadium oxide was coated on the LbL-assembled MWCNT electrode to induce pseudocapacitance, hence enhancing the overall capacitance of the fabricated WSS. Both the cyclic stability of the WSS and the viscosity of the electrolyte could be optimized by controlling the mixing ratio of PC to ACN. As a result, the fabricated WSS exhibits an areal capacitance of 5.23 mF cm^–2 at 0.2 mA cm^–2, an energy density of 1.86 μ W h cm^–2, and a power density of 8.5 mW cm^–2, in addition to a high cyclic stability with a 94% capacitance retention after 10 000 galvanostatic charge–discharge cycles. This work demonstrates a great potential of the fabricated scalable WSS in the application to high-performance textile electronics as an integrated energy storage device

Encapsulated, High-Performance, Stretchable Array of Stacked Planar Micro-Supercapacitors as Waterproof Wearable Energy Storage Devices

We report the fabrication of an encapsulated, high-performance, stretchable array of stacked planar micro-supercapacitors (MSCs) as a wearable energy storage device for waterproof applications. A pair of planar all-solid-state MSCs with spray-coated multiwalled carbon nanotube electrodes and a drop-cast UV-patternable ion-gel electrolyte was fabricated on a polyethylene terephthalate film using serial connection to increase the operation voltage of the MSC. Additionally, multiple MSCs could be vertically stacked with parallel connections to increase both the total capacitance and the areal capacitance owing to the use of a solid-state patterned electrolyte. The overall device of five parallel-connected stacked MSCs, a microlight-emitting diode (μ-LED), and a switch was encapsulated in thin Ecoflex film so that the capacitance remained at 82% of its initial value even after 4 d in water; the μ-LED was lit without noticeable decrease in brightness under deformation including bending and stretching. Furthermore, an Ecoflex encapsulated oximeter wound around a finger was operated using the stored energy of the MSC array attached to the hand (even in water) to give information on arterial pulse rate and oxygen saturation in the blood. This study suggests potential applications of our encapsulated MSC array in wearable energy storage devices especially in water