Template-free synthesis of novel Co3O4 micro-bundles assembled with flakes for high-performance hybrid supercapacitors

Abstract In this paper, a novel Co3O4 micro-bundles structure (Co3O4 MBs) was obtained at 120 °C after a hydrothermal reaction for 24 h and followed by an annealing treatment at 300 °C in air. The unique Co3O4 MBs are constructed by many adjacent flakes with 0.4 μm in thickness, and exhibit a large surface area of 81.2 m2 g−1 and a mean pore diameter of 6.14 nm, which may facilitate a sufficient contact with electrolyte and then shorten the diffusion pathway of ions. A remarkable electrochemical behavior including specific capacity of 282.3 C g−1 at 1 A g−1 and 205.9 C g−1 at 10 A g−1, and an excellent cycling performance with 74.6% capacity retention after 4000 charge-discharge process at 5 A g−1 are achieved when the test of Co3O4 MBs-modified electrode is performed using three-electrode configuration. Additionally, a hybrid supercapacitor (HSC) was fabricated with the obtained Co3O4 MBs as positive electrode and commercial activated carbon (AC) as negative electrode. The HSC exhibits a specific capacity of 144.1 C g−1 at 1 A g−1 and 126.4% capacity retention after 5000 cycles at 5 A g−1. An energy density of 38.5 W h kg−1 can be obtained at a power density of 962.0 W kg−1, and 29.5 W h kg−1 is still retained at 8532.5 W kg−1. The simple synthetic strategy can be applicable to the synthesis of other transition metal oxides with superior electrochemical performance.