Sonochemical synthesis of battery-type ZnCo2O4 electrode material with huge specific surface area for advanced hybrid supercapacitors

Sonochemistry is a novel and efficient method for the synthesis of electrode materials within micro-/nano-scale. In this work, the ZnCo2O4 nanoparticles (NPs) and chain-like ZnCo2O4 nanostructures, namely ZnCo2O4–7.5 and ZnCo2O4–9.5, were sonochemically prepared by controlling the pH value of reaction system combined with an extra calcination. The ZnCo2O4–7.5 NPs exhibited a larger specific surface area (SSA) of 148.77 m2 g−1, and presented better electrochemical properties such as a high specific capacity (Cs) of 331.2C g−1 under 2 A g−1 along with 82.5 % rate performance at 10 A g−1. As for the ZnCo2O4–9.5 nanostructure, it delivered an inferior Cs of 274.8C g−1 and showed a moderate rate capability with 75.6 % capacity retention, accordingly. The hybrid supercapacitor (HSC) device was assembled using such ZnCo2O4–7.5 NPs (ZnCo2O4–9.5 nanostructure) as cathode and activated carbon (AC) as anode to explore the application potential in the field of electrochemical energy storage. After 7000 cycles at the current density of 8 A g−1, both ZnCo2O4–7.5//AC and ZnCo2O4–9.5//AC HSCs showed outstanding cyclic stabilities with 100.4 % and 105.1 % of initial capacity retention, respectively. Meanwhile, the ZnCo2O4–7.5//AC HSC delivered a high energy density (Ed) of 38.1 W h kg−1 at the power density (Pd) of 1002.0 W kg−1, and it could still hold 26.3 W h kg−1 at the higher Pd of 9136.5 W kg−1. In contrast, the ZnCo2O4–9.5//AC HSC presented a slightly inferior Ed of 36.8 W h kg−1 at 1104.7 W kg−1. The both types of ZnCo2O4–7.5 and ZnCo2O4–9.5 electrode materials demonstrate excellent electrochemical property, and they can be expected to show brilliant application potential in the field of electrochemical energy storage & conversion when served as electrode materials for high-performance hybrid supercapacitors.