New insight into the effect of fluorine doping and oxygen vacancies on electrochemical performance of Co₂MnO₄ for flexible quasi-solid-state asymmetric supercapacitors

Anion doping and oxygen-defect creation have been extensively employed to modify the electronic properties and increase concentration of electrochemically active sites of electrode materials for electrical energy storage technologies; however, comprehensive study of the roles of anion doping and oxygen vacancy on the enhancement of electrochemical performance is not clear. Herein, we provide new insight into the effect of fluorine dopant and oxygen vacancy on electrochemical performance of fluorine-doped oxygen-deficient Co2MnO4 (F-Co₂MnO_4-x) nanowires grown on carbon fiber (CF) as advanced electrode materials for supercapacitor. An experimental and theoretical study reveals that the structural and electronic properties in F-Co₂MnO_4-x is effectively tuned by introducing F dopants and oxygen vacancies, synergistically increasing electrical conductivity and providing rich Faradaic redox chemistry. The resultant F-Co2MnO4-x achieves a high specific capacity of 269 mA h g⁻¹ at 1 A g⁻¹, and superior cyclic stability with 93.2% capacity retention after 5000 cycles at 15 A g⁻¹. A flexible quasi-solid-state asymmetric supercapacitor (ASC) is constructed with F-Co₂MnO_4-x/CF as the positive electrode and Fe₂O₃/CF as the negative electrode. The ASC device exhibits a high energy density of 64.4 W h kg−1 at a power density of 800 W kg⁻¹. Significantly, the device yields 89.9% capacitance retention after 2000 bending tests at a bending angle ranging from 0 to 30°, demonstrating the high integration of excellent mechanical flexibility and cycling stability.