Phosphate ion-functionalized nickel-cobalt layered double hydroxide nanosheets derived from metal-organic framework compounds for high-performance asymmetric supercapacitors

Abstract

The modification by functionalized ions (surface modification or doping) presents facile and efficient access to enhance the electrochemical performance of electrode materials. However, the effect of functionalized ions on the structure-performance relationship of electrode materials is not yet apparent. Herein, we develop a novel phosphate ion-functionalized nickel-cobalt layered double hydroxide nanosheet (Ni-Co-P80) derived from metal-organic framework compounds prepared as anode material for supercapacitors. The obtained Ni-Co-P80 not only remains characterized by high specific surface area and porosity, but also possesses more active sites and higher electrical conductivity with phosphate modification, thus improving the charge transfer kinetics. The electrochemical test results show that the highest specific capacitance of Ni-Co-P80 modified with phosphate ions increases by 49.7% compared to pure phase LDH. More impressively, the assembled asymmetric supercapacitor exhibits an excellent energy density of 64.89 Wh kg-1 at a power density of 1600 W kg-1 with an ultralong cyclic performance of 77.78% capacitance retention after 5000 cycles. This study explicitly demonstrates the remarkable enhancement of specific capacitance of layered double hydroxide following modification with phosphate ions. It brings a prospective pathway toward the rational design of LDH-based high-performance asymmetric supercapacitors.