A true cable assembly with a carbon nanotube sheath and nickel wire core: a fully flexible electrode integrating energy storage and electrical conduction

Abstract

Fiber-shaped supercapacitors integrating energy storage and electrical conduction are new forms of energy supplying devices that would occupy minimum space and would be of minimum cost. The bottleneck in this field is the lack of structurally innovative electrode materials. Herein, we describe a fully flexible cable with excellent mechanical strength and conductivity. The sheath of the cable is composed of an interconnected carbon nanotube (CNT) network with a packing density comparable to highly aligned CNT forests, which is directly coupled to the underlying Ni wire core via a spontaneous solution process with scalability on an industrial scale. The wire-shaped capacitors using two parallel CNT@Ni cables and KOH/polyvinyl alcohol gel electrolyte offer remarkable electrochemical performances, including a wide voltage window (>1.4 V), high volumetric capacitance (13.8 mF cm⁻³ at 95 mA cm⁻³), and long cycle life. Moreover, the device can deliver an energy density of 3.8 mW h cm⁻³ and a power density of 1590 mW cm⁻³. The energy density is comparable to that of a 4 V/500 μA h thin-film lithium battery, while the power density is two orders of magnitude higher than that of the battery. More impressively, the CNT@Ni cable-based supercapacitor can utilize the Ni wire to transport the energy while storing charges in the CNT sheath simultaneously.