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

Oxygen‐deficient bismuth oxide (r‐Bi 2 O 3 )/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‐Bi 2 O 3 /GN exhibits high flexibility, remarkable tensile strength (55.1 MPa), and large mass loading of 9.8 mg cm −2 . The flexible r‐Bi 2 O 3 /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 Bi 2 O 3 , delivering significantly improved capacitive values than the untreated Bi 2 O 3 flexible electrode, and ultrahigh gravimetric capacitance of 1137 F g −1 (based on the mass of r‐Bi 2 O 3 ) can be obtained, achieving 83% of the theoretical value (1370 F g −1 ). Flexible asymmetric supercapacitor is fabricated with r‐Bi 2 O 3 /GN/BC and Co 3 O 4 /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.