Highly flexible and large areal/volumetric capacitances for asymmetric supercapacitor based on ZnCo2O4 nanorods arrays and polypyrrole on carbon cloth as binder-free electrodes

Abstract

Flexible asymmetric supercapacitor (FAS), as a promising candidate for wearable or flexible electronic devices, draws great attention since it exhibits the flexibility and enhanced areal/volumetric capacitances comparing with the symmetrical Faraday capacitors. Herein, we grow unique ZnCo2O4 nanorods arrays on carbon cloth (ZnCo2O4-CF) by a simple hydrothermal method, and the electrode exhibits a remarkable areal (volumetric) capacitance of 5.18 F cm−2 (167.5 F cm−3) at 5 mA cm−2 and exceptional capacitance retention of 92.8% after 3000 cycles. A FAS was fabricated using ZnCo2O4-CF as the positive and PPy-CC (deposition of Polypyrrole on carbon cloth) as negative electrodes, respectively. Especially, the asymmetric electrodes help the device to exhibit a wide potential window of 1.6 V and a high areal (volumetric) capacitance of 1.8 F cm−2 (148 F cm−3). As a result, the FAS shows a maximum energy of 2.3 mW h cm−2 (18.9 mW h cm−3) at a power density of 7.82 mW cm−2 (82.2 mW cm−3) and a good stability after 5000 cycles at a current density of 5.0 A cm−2. Furthermore, the FAS shows good flexibility and can withstand bending at different angles while keeping electrochemical performance constant.