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.