Heterostructure of nickel cobalt metaphosphate nanoneedles decorated with NiMn layered double hydroxide nanosheets for supercapacitors

Abstract

Constructing heterostructured electrode materials with well-designed components and nanostructures is a promising strategy to enhance the electrochemical performance of supercapacitors. In this study, a rational heterostructured composite of nickel cobalt metaphosphate (Ni0.4Co0.6(PO3)2) nanoneedles decorated with NiMn layered double hydroxide (NiMn-LDH) nanosheets has been fabricated on carbon paper (CP) substrate by sequential hydrothermal method, phosphorization, and hydrothermal treatment. This well-aligned Ni0.4Co0.6(PO3)2@NiMn-LDH core–shell heterostructure not only exposes abundant electroactive sites to participate in reversible electrochemical reactions, but also offers short pathways for rapid electron/ion transport and buffers volume changes during charging/discharging processes. Benefiting from these structural merits and component synergistic effect, the self-supporting Ni0.4Co0.6(PO3)2@NiMn-LDH electrode displays a high capacity of 1147.9C/g (1913 mC cm−2) at 1 A/g and a capacity retention of 95.2 % after 5000 cycles in a tri-electrode cell. Besides, the assembled aqueous Ni0.4Co0.6(PO3)2@NiMn-LDH-based hybrid supercapacitor presents an energy density of 71.5 Wh kg−1 (0.24 mWh cm−2) at a power density of 732.9 W kg−1 (2.5 mW cm−2) and retains 94.4 % of the initial capacity over 10,000 cycles. This work provides an efficient hybridization approach to design high-performance electrode materials for advanced energy storage devices.