Using Ca2.9Nd0.1Co4O9+δ Perovskites to Convert a Flexible Carbon Nanotube Based Supercapacitor to a Battery-Like Device

Abstract This work reports the electrochemical performance of flexible carbon nanotube (CNT) based energy storage devices fabricated with and without Ca2.9Nd0.1Co4O9+δ perovskite microplates. According to the scanning electron microscopy (SEM), the perovskite microplates have irregular edges and most of them (65%) have sizes in the range of 1-3 µm. The analysis by X-ray diffraction revealed that the perovskite microplates have a monoclinic structure. The electrochemical studies demonstrated that the flexible device made exclusively with CNT's electrodes store charge by electric double layer mechanisms and showed a maximum capacitance and energy density of 53.6 F/g and 16.7 Wh/Kg, respectively. This last device behaved as a typical supercapacitor. Surprisingly, the capacitance and energy density of the device increased ≈10.57 and ≈4.68 times, respectively, after introducing the perovskite microplates into the anode electrode. The enhancement of both parameters in the device fabricated with perovskite was associated with the fact that the device stored charge efficiently by simultaneous redox reactions of the Ca, Nd, and Co elements (this was confirmed by XPS measurements). The perovskite based device behaved as a battery since stabilization of the output voltage was observed after releasing all the energy stored by redox reactions (capacitive part). Hence, the results showed in this work give an insight about how to use perovskite materials to increase the capacitance and energy density of flexible energy storage devices by redox reactions.