Hierarchical pipe cactus-like Ni/NiCo-LDH core–shell nanotube networks as a self-supported battery-type electrode for supercapacitors with high volumetric energy density

Abstract

High-performance yet thin hybrid supercapacitors (HSC) are urgently needed to meet the increasing demands of wearable and portable electronic devices. Nevertheless, most of the current electrode designs employed to enhance the electrode capacity and conductivity provide limited volumetric capacity because they commonly rely on macroscopic, heavy support materials such as nickel foam or carbon cloth. Hence, micro- and nanostructuring strategies towards tailored electrode architectures will be vital for their utilization in practical applications. Herein, a three-dimensional (3D) self-supported hierarchical electrode was obtained by directly growing NiCo layered double hydroxide (NiCo-LDH) nanosheets on a Ni nanotube network (Ni-NTNW) via electrodeposition. The resulting electrode takes advantage of the large interface and the high redox activity of the two-dimensional (2D) coating nanosheets, whose properties are augmented by the highly porous network architecture of the one-dimensional (1D) Ni-NTNW support, which enables fast mass transfer and acts as a “highway” for fast electron transfer. The fabricated NiCo-LDH@Ni-NTNW architecture replicates the thickness of the parent template (20 μm) employed for the electroless plating of the Ni-NTNW, resulting in an ultrathin battery-type electrode with a superb volumetric capacity of 126.4 C cm⁻³, remarkable rate capability, and outstanding cycling stability. Additionally, the assembled NiCo-LDH@Ni-NTNW//activated carbon (AC) HSC can deliver a high volumetric capacitance of 76.7 F cm⁻³ at a current density of 1 mA cm⁻². Meanwhile, it exhibits a high energy density of 14.7 mWh cm⁻³ with a maximum power density of 4769 mW cm⁻³, surpassing most state-of-the-art supercapacitors that deliver high volumetric energy density. As such, hybrid core–shell nanotube networks represent an up-and-coming design paradigm for high-performance supercapacitor devices in portable devices.