Compact and porous 3D MnO2/holey graphene films for high areal and volumetric performance in supercapacitors with high-thick electrodes

Most manganese oxide-based electrodes used for energy-storage applications suffer from poor ion and electron transport, particularly at high mass loadings and with thick electrodes. To counter this issue, 3D electrodes were developed; however, enhancing their areal and volumetric performance at high mass loadings is still a challenge. In this study, highly compact and 3D porous manganese dioxide and holey reduced graphene oxide (3D MnO2/ HRGO) composite films were developed to ensure a high performance in supercapacitors at electrode thicknesses greater than 100 pm. The thick composite films were fabricated by the self-limiting deposition of MnO2 on 3D HRGO hydrogel scaffolds followed by capillary evaporation-induced drying. The 3D MnO2/HRGO electrodes optimized at a thickness of 216 mu m showed outstanding specific areal and volumetric capacitances of 2.3 F cm-2 and 108.0 F cm-3 at 1 mA cm-2 and an impressive rate capability with a capacitance retention of 72.2% in the range of 1-40 mA cm-2. Furthermore, supercapacitors assembled with the 3D MnO2/HRGO electrodes with high mass loadings exhibited impressively high areal and volumetric energy densities of 149.7 mu Wh cm-2 and 2.8 mWh cm-3, respectively.