Flexible Asymmetric Micro‐Supercapacitors Based on Bi2O3 and MnO2 Nanoflowers: Larger Areal Mass Promises Higher Energy Density

A flexible asymmetric supercapacitor (ASC) with high energy density is designed and fabricated using flower‐like Bi₂O₃ and MnO₂ grown on carbon nanofiber (CNF) paper as the negative and positive electrodes, respectively. The lightweight (1.6 mg cm^?2), porous, conductive, and flexible features make the CNF paper an ideal support for guest active materials, which permit a large areal mass of 9 mg cm^?2 for Bi₂O₃ (≈85 wt% of the entire electrode). Thus, the optimal device with an operation voltage of 1.8 V can deliver a high energy density of 43.4 μWh cm^?2 (11.3 W h kg^?1, based on the total electrodes) and a maximum power density of 12.9 mW cm^?2 (3370 W kg^?1). This work provides an example of large areal mass and flexible electrode for ASCs with high areal capacitance and high energy density, holding great promise for future flexible electronic devices.