Zn doping induced local lattice expansion for hierarchical hollow NiCo-LDH toward enhanced electrochemical performance in asymmetric supercapacitors

The exploration of transition metal-based electrode materials for asymmetric supercapacitors has garnered considerable interest owing to their potential to achieve high-energy storage and demonstrate outstanding electrochemical performance. In this study, we designed and synthesized Zn-doped NiCo layered double hydroxide (LDH), a hollow supercapacitor electrode material, through a facile ion exchange method at room temperature. Doping Zn ions results in an increased interlayer spacing expanding from 0.815 nm (ZIF-67@NiCo-LDH) to 0.874 nm (ZnNiCo-LDH-7), which facilitates sufficient penetration of the electrolyte and accelerates the charge transfer kinetics. Moreover, by employing the metal-organic framework ZIF-67 as a precursor, ZnNiCo-LDH nanosheets assembled in hollow nanocages exhibit remarkable electrochemical performance due to their large contact area with electrolytes and superior electrical conductivity. The synthesized ZnNiCo-LDH electrode material achieves a high specific capacitance of 1908 F g−1 at 1 A g−1. When integrated into an asymmetric supercapacitor, in combination with activated carbon (AC), the device delivers an outstanding energy density of 41.5 Wh kg−1 at a power density of 825 W kg−1. Notably, the assembled device shows exceptional cycling stability, retaining 120 % of its initial specific capacitance even after 5000 cycles at a current density of 5 A g−1. The extraordinary performance and remarkable stability are mainly due to Zn ion doping-induced local lattice expansion and the hierarchical hollow nanocage structure, which underscores its highly promising potential in supercapacitor applications.