Fabrication of dual-hollow heterostructure of Ni2CoS4 sphere and nanotubes as advanced electrode for high-performance flexible all-solid-state supercapacitors

High-energy-density and flexible supercapacitors have shown numerous application potential in modern portable electronics. However, the relatively low specific capacity, poor rate retentions, and limited durability have hindered their implement. Herein, a novel hierarchical dual-hollow electrode, composed of a hollow Ni2CoS4 sphere and outer hollow Ni2CoS4 nanotubes (Ni2CoS4HS-HTs), is elaborately constructed. The Ni2CoS4HS-HT-5 exhibits a high specific capacity of 817.5 C g(-1) at a current density of 1 A g(-1) with remarkable rate retention of 75.3% at 50 A g(-1). In an all-solid-state asymmetric supercapacitor of Ni2CoS4HS-HT-5//CAC, a high capacitance of 1511.5 mF cm(-2) at 5 mA cm(-2) is obtained with an exceptional energy density of 13.6 mWh cm(-3) at a power density of 92.6 mW cm(-3). In addition, the capacity retention reaches 96% over 2000 cycles at 20 mA cm(-3) , implying the outstanding durability. The flexibility and mechanical stability are demonstrated by the intact electrochemical performances under different bending angles. As a proof-of-concept, two Ni2CoS4HS-HT-5//CACs in series could successfully illuminate 31 LED indicators for more than 8 mins. These fascinating electrochemical performances benefit from the novel electrode structure and depict great potential for modern energy storage applications. (C) 2019 Elsevier Inc. All rights reserved.