Design of Hierarchical NiCo@NiCo Layered Double Hydroxide Core–Shell Structured Nanotube Array for High-Performance Flexible All-Solid-State Battery-Type Supercapacitors

A novel hierarchical nanotube array (NTA) with a massive layered top and discretely separated nanotubes in a core–shell structure, that is, nickel–cobalt metallic core and nickel–cobalt layered double hydroxide shell (NiCo@NiCo LDH), is grown on carbon fiber cloth (CFC) by template-assisted electrodeposition for high-performance supercapacitor application. The synthesized NiCo@NiCo LDH NTAs/CFC shows high capacitance of 2200 F g⁻¹ at a current density of 5 A g⁻¹, while 98.8% of its initial capacitance is retained after 5000 cycles. When the current density is increased from 1 to 20 A g⁻¹, the capacitance loss is less than 20%, demonstrating excellent rate capability. A highly flexible all-solid-state battery-type supercapacitor is successfully fabricated with NiCo LDH NTAs/CFC as the positive electrode and electrospun carbon fibers/CFC as the negative electrode, showing a maximum specific capacitance of 319 F g⁻¹, a high energy density of 100 W h kg⁻¹ at 1.5 kW kg⁻¹, and good cycling stability (98.6% after 3000 cycles). These fascinating electrochemical properties are resulted from the novel structure of electrode materials and synergistic contributions from the two electrodes, showing great potential for energy storage applications.