Dual role of nickel foam in NiCoAl-LDH ensuring high-performance for asymmetric supercapacitors

Abstract

Sluggish ion diffusion and low electronic conductivity are two pivotal obstacles that prevent the realization of the theoretical capacitance of layered double hydroxides (LDHs). Herein, hierarchical three-dimensional (3D) porous networks of nickel–cobalt–aluminum layered hydroxide nanosheets (NSs) were sequentially grown and fabricated on a flexible conductive nickel foam substrate (NF) by a facile hydrothermal method. Within this material, the nickel foam acted as the structural support and at the same time as the slow-release nickel source, which could adjust the ratio of Ni and Co ions without changing the morphology of electrode materials. The NiCoAl-LDH/NF was demonstrated to have an ultra-high areal capacitance reaching 5691.25 mF cm⁻² at a current density of 1 mA cm⁻² when the ratio of Ni : Co was 1 : 1.5, which is due to the synergistic effect between Ni and Co ions. Moreover, the obtained NiCoAl-LDH/NF was used as the anode material while the porous activated carbon (PAC) was used as the cathode material and assembled into an asymmetric supercapacitor. The maximum energy density of the optimal NiCoAl-LDH/NF//PAC device was 41.44 W h kg⁻¹ at a power density of 799.9 W kg⁻¹, with the voltage window reaching 1.6 V. This strategy provides a simple method to synthesize LDH-based electrode materials with high-capacitance for supercapacitors.