Oxygen-Deficient Bismuth Oxide/Graphene of Ultrahigh Capacitance as Advanced Flexible Anode for Asymmetric Supercapacitors

Oxygen-deficient bismuth oxide (r-Bi₂O₃)/graphene (GN) is designed, fabricated, and demonstrated via a facile solvothermal and subsequent solution reduction method. The ultrafine network bacterial cellulose (BC) as substrate for r-Bi₂O₃/GN exhibits high flexibility, remarkable tensile strength (55.1 MPa), and large mass loading of 9.8 mg cm⁻². The flexible r-Bi₂O₃/GN/BC anode delivers appreciable areal capacitance (6675 mF cm⁻² at 1 mA cm⁻²) coupled with good rate capability (3750 mF cm⁻² at 50 mA cm⁻²). In addition, oxygen vacancies have great influence on the capacitive performance of Bi₂O₃, delivering significantly improved capacitive values than the untreated Bi₂O₃ flexible electrode, and ultrahigh gravimetric capacitance of 1137 F g⁻¹ (based on the mass of r-Bi₂O₃) can be obtained, achieving 83% of the theoretical value (1370 F g⁻¹). Flexible asymmetric supercapacitor is fabricated with r-Bi₂O₃/GN/BC and Co₃O₄/GN/BC paper as the negative and positive electrodes, respectively. The operation voltage is expanded to 1.6 V, revealing a maximum areal energy density of 0.449 mWh cm⁻² (7.74 mWh cm⁻³) and an areal power density of 40 mW cm⁻² (690 mW cm⁻³). Therefore, this flexible anode with excellent electrochemical performance and high mechanical properties shows great potential in the field of flexible energy storage devices.