S. Lee, C. Park, H. Ahn
Keywords: ammonium vanadate, conducting polymer, intercalation pseudocapacitance, nanofiber, sonochemical method
Summary:The low electrical conductivity and slow rate capability of vanadium oxide limit its utilization in high rate energy storage applications. Many studies are trying to overcome these drawbacks, but it remains a challenge. In this study, we propose a simple strategy to produce conducting polymer-intercalated ammonium vanadate nanofiber composites exhibiting high capacitance and high rate capability. Ammonium vanadate nanofibers (S-AVNFs) are easily prepared in aqueous solution by ultrasonicating a mixture of vanadium pentoxide and ammonium persulfate in water for 30 min. In addition, the poly(3,4-ethylene dioxythiophene) (PEDOT)-intercalated ammonium vanadate nanofiber composites are prepared by ultrasonicating the S-AVNF solution with 3,4-ethylene dioxythiophene (EDOT) monomers for 3 hrs. PEDOT-intercalated ammonium vanadate nanofiber composites (S-EAVNF) synthesized using the sonochemical method are utilized as a pseudocapacitive material, and they exhibit high rate supercapacitive performances. The electrochemical charge storage mechanism of the S-EAVNF was analyzed by sweep analysis, and it revealed a pseudocapacitive current contribution of 81% of the total charge at a scan rate of 30 mV s-1. The S-EAVNF electrode showed higher rate capability and specific capacitance than S-AVNF. This is because the electrical conductivity was improved by the intercalation of PEDOT, and the diffusion of K+ ions was enhanced by expansion of the interlayer distance of the lattice of vanadate nanofibers. In addition, the ex-situ XRD analysis confirmed that the intercalation/de-intercalation of K+ ions reversibly occurred in an S-EAVNF electrode. The AC//S-EAVNF asymmetric device showed a maximum energy density of 20.7 Wh kg-1 (27.9 μWh cm-2) at a power density of 600 W kg-1 (0.8 mW cm-2) and an energy density of 8.2 Wh kg-1 (11.2 μWh cm-2) even at an extremely high power density of 18,000 W kg-1 (24.3 mW cm-2), signifying the high rate capability of the AC//S-EAVNF asymmetric device. Moreover, it shows excellent capacitance retention of 87% after 1,000 cycles. These results suggest that the conducting polymer-intercalated ammonium vanadate nanofiber composites are promising candidates for high rate and high energy storage devices.