Facile Synthesis of 3D Cu(OH)2@NiCo-Binary Hydroxide Core-Shell Nanotube Arrays with High Mass Loading for High-Performance Asymmetric Supercapacitors

Reasonably designing nanostructures with high electrochemical activity is the key to improving the redox chemical properties of battery-type materials. In this work, three-dimensional layered Cu(OH)@NiCo double hydroxide nanotube arrays have been synthesized by in situ etching and solvothermal methods successively. The core-shell array of Cu(OH)(2) nanotubes was encapsulated by NiCo-binary hydroxide (NiCo-BH) nanosheets, with a mass load of 10.7 mg cm(-2), reaching a commercial level. The electrode material of the nanotube array structure exposes abundant active sites that are conducive to redox reactions and abundant microspaces for accelerating the electron and ion transport. Moreover, without adding conductive agents and binders but directly depositing on the current collector results in their homogeneous contact on the current collector and endows a binder-free electrode, further accelerates electron transport, and provides robust support. After optimization, the nickel cobalt content ratio in the Cu(OH)(2)@NiCo-BH electrode material is 2:1, and the mass load is 10.7 mg cm(-2). As verified by electrochemical testing, the material exhibits an ultrahigh area capacitance of 13.5 F cm(-2) (1262 F g(-1)) at 1 mA cm(-2), and its 85% capacitance maintenance is still achieved at 20 mA cm(-2). Meanwhile, it has remarkable stability in cycling, with a 94% of cap retention after 5000 cycles. In the asymmetric ultracapacitor constructed with Cu(OH)(2)@NiCo-BH//activated carbon (AC) as the positive electrode, it exhibits a high energy density of 0.762 mWh cm(-2) at 4 mW cm(-2), and the retention of capacitance is still maintained at 89% after 5000 cycles. Thus, the material shows significant potential for high-energy and high-power storage applications.