Printed flexible solid-state microsupercapacitor with highly-stable aqueous cobalt-based inks

Abstract

Cobalt-based nanomaterials are among the most noticed candidates for manufacturing supercapacitive electrodes. Inkjet-printing is an emerging technique for fabricating miniaturized devices. In this work, highly flexible microsupercapacitors (MSCs) are manufactured, using a pseudocapacitive (C = 900 F‌ g−1 at 1 A g−1) Co-oxide-hydroxide water-based and ultra-stable (up to 12 months) ink on paper. The synthesized capacitive active material consists of cobalt-oxide nanocubes and cobalt-hydroxide hexagonal nanoflakes. Conductive (Rs = 13 Ω/□) silver nanowire networks serve as current collectors, and the morphology of cobalt oxide-hydroxide structures and the developed ink features, allow for printing well-detailed and homogeneous patterns. The inkjet-printed symmetric and asymmetric devices show notable areal specific capacitances of 35.68 mF cm−2 and 23.60 mF cm−2 at a current density of 0.1 mA cm−2, respectively. The asymmetric devices deliver impressive energy and power densities of 2.76 μW h cm−2 (4.10 W h kg−1) and 646 μW cm−2 (959 W kg−1), respectively. A thorough study on the cyclic and mechanical stability of the flexible devices resulted in perfect capacitance maintenance of 94.3 % after 10,000 charge and discharge cycles and retention of over 80 % even after 1000 cycles of successive bending and folding. The extensive study of capacitance retention following folding under various obtuse and reflex angles, which can be regarded as an important step toward characterizing flexible devices suitable for being utilized in wearable electronics, is carried out for the first time to the best of our knowledge. The findings of this study clearly illustrate the prospects of using the inkjet-printing technique to fabricate high-performance MSC devices appropriate for integration with flexible and wearable electronics.