Nickel cobaltite@poly(3,4-ethylenedioxypyrrole) and carbon nanofiber interlayer based flexible supercapacitors

Abstract

Binder free flexible symmetric supercapacitors are developed with nickel cobaltite micro-flower coated poly(3,4-ethylenedioxypyrrole) (NiCo₂O₄@PEDOP) hybrid electrodes. The free standing films of carbon nano-fibers (CNFs), synthesized by electrospinning, were sandwiched between the NiCo₂O₄@PEDOP hybrid and the electrolyte coated separators on both sides of the cells. The CNF film conducts both ions and electrons, and confines the charge at the respective electrodes, to result in an improved specific capacitance (SC) and energy density compared to the analogous cell without the CNF interlayers. A high SC of 1775 F g⁻¹ at a low current density of 0.96 A g⁻¹ and an SC of 634 F g⁻¹ achieved at a high current density of 38 A g⁻¹ coupled with an SC retention of ∼95% after 5000 charge–discharge cycles in the NCO@PEDOP/CNF based symmetric supercapacitor, are performance attributes superior to those achieved with NCO and NCO/CNF based symmetric cells. The PEDOP coating serves as a highly conductive matrix for the NCO micro-flowers and also undergoes doping/de-doping during the charge–discharge, thus amplifying the overall supercapacitor response, compared to the individual components. The CNF interlayers show reasonably high ion-diffusion coefficients for K⁺ and OH⁻ propagation, implying facile pathways available for the movement of ions across the cross-section of the cell, and they also serve as ion reservoirs. The electrode morphologies remain unaffected by cycling in the presence of the CNF interlayer. LED illumination and a largely unaltered charge storage response were achieved in a mutli-cell configuration, proving the potential for this approach in practical applications.