High-performance magnesium ion asymmetric Ppy@FeOOH//Mn3O4 micro-supercapacitor

Abstract

Micro-supercapacitors (MSCs) are attractive electrochemical energy storage devices owing to their high power density and extended cycling stability. However, relatively low areal energy density still hinders their practical applications. Here, an asymmetric Mg ion MSC with promising high energy density is fabricated. Firstly, indium tin oxide (ITO) NWs were synthesized by chemical vapor deposition as the excellent current collector. Subsequently, nanostructured Mn3O4 and Ppy@FeOOH were deposited on the laser-engraved interdigital structure ITO NWs electrodes as the positive and negative electrodes, respectively. Beneficial from the hierarchical micro-nano structures of active materials, high conductive electron transport pathways, and charge-balanced asymmetric electrodes, the obtained MSC possesses a high potential window of 2.2 V and a high areal capacitance of 107.3 mF cm−2 at 0.2 mA cm−2. The in-situ XRD, VSM, and ex-situ XPS results reveal that the primary energy storage mechanism of Mg ions in negative FeOOH electrode is Mg ions de-/intercalation and phase transition reaction of FeOOH. Furthermore, the MSC exhibits a high specific energy density of 71.18 μWh cm−2 at a power density of 0.22 mWh cm−2 and capacitance retention of 85% after 5000 cycles with unvaried Coulombic efficiency. These results suggest promising applications of our MSC in miniaturized energy storage devices.