NiCo-layered double hydroxide with cation vacancy defects for high-performance supercapacitors

Layered double hydroxides (LDHs) with high specific capacitances have proved to be promising electrode materials for supercapacitors. However, the drawbacks of their insulating nature and limited active sites hinder further capacity enhancement. Herein, the NiCo-LDH/NF with abundant cobalt ion vacancy defects (D-NiCo-LDH/NF) was synthesized based on the memory effect. Revealed by the density functional theory (DFT) calculations, the cobalt ion vacancy induces more active electrons to near the Fermi level, thus enhancing conductivity and accelerating charge transfer. Profiting from the optimized local electronic structure and more exposed active sites, the as-synthesized d-NiCo-LDH/NF exhibits unexpected specific capacity of 361 mAh g − 1 and specific capacitance of 3200 F g − 1 at the current density of 1 A g − 1, much higher than that of the pristine NiCo-LDH/NF electrode (282 mAh g − 1 and 2500 F g − 1 at 1 A g − 1). Furthermore, assembled asymmetric supercapacitor (ASC) with d-NiCo-LDH/NF and activated carbon (AC) working as the positive electrode and negative electrode material, respectively, displays a superior energy density of 53 Wh kg−1 under a power density of 752 W kg−1 with outstanding cycle stability of 94.7% retention after 5000 cycles.