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

In this paper, a novel Co3O4 micro-bundles structure (Co3O4 MBs) was obtained at 120 degrees C after a hydrothermal reaction for 24 h and followed by an annealing treatment at 300 degrees C in air. The unique Co3O4 MBs are constructed by many adjacent flakes with 0.4 mu m in thickness, and exhibit a large surface area of 81.2 m(2) 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.