High performance NiCo-LDH//Fe2O3 asymmetric supercapacitors based on binder-free electrodes with dual conductive networks

Freestanding and binder-free electrodes with dual conductive networks were designed and prepared for asymmetric supercapacitors (ASCs), within which hollow and porous carbon nanofiber cloth (CNFs) was employed as the inner-conductive and electrochemical-active substrate while a uniform and ultrathin graphene layer served as the conductive and protective outer layer, aiming to protect the volume contraction/expansion of oxide/ hydroxide during cycling and bridge the conductive path of fiber-to-fiber and (hydr)oxide-(hydr)oxide. The synergistic effect of substrate optimization, outer conductive network construction along with structural/ compositional modification give rise to enhanced electronic conductivity, increased electroactive reaction sites, improved structural stability as well as accelerated kinetics, leading to remarkably rate capability and outstanding cyclic stability. Based on the weight of the whole electrode (including CNFs substrate), Fe2O3@CNFs-rGO anode achieved an outstanding specific capacitance of 488F/g at 2 A/g and excellent cycling stability of 83.5% capacitance retention after 5000 cycles at 4 A/g, whereas the specific capacitance of Ni-Co LDH@CNFs-rGO cathode reached 932 and 396F/g at 2 and 20 A/g, respectively, showing superb rate performance. Impressively, the assembled Ni-Co LDH@CNFs-rGO//Fe2O3@CNFs-rGO supercapacitor delivered an energy density of 45 and 18.7 Wh/kg when the power density was 1528 and 35400 W/kg, respectively. Such a reasonable structure design of electrode materials provides a new way to improve the conductivity, cycling stability and even the electrochemical performance.

Automated summary

By designing freestanding and binder-free electrodes with dual conductive networks, using hollow and porous carbon nanofiber cloth and ultrathin graphene layer as the inner and outer conductive layers, the electronic conductivity, electroactive reaction sites, structural stability, and kinetics of asymmetric supercapacitors (ASCs) can be improved. This design enhances the rate capability and cyclic stability of ASCs.