Effect of reaction temperature on the amorphous-crystalline transition of copper cobalt sulfide for supercapacitors

Abstract

Amorphous and crystalline copper cobalt sulfides are successfully synthesized via a hydrothermal method at different temperatures and researched as electrode materials for supercapacitor. The reaction mechanisms during the sulfidation and hydrothermal processes are investigated and clarified. It is demonstrated that the hydrothermal temperature is a crucial factor for the crystallinity, morphology and electrochemical performance of CuCo2S4. Among all the samples, the CuCo2S4 synthesized at 150 °C shows the highest specific capacitance of 515 F g-1 at 1 A g−1 as well as good cycling stability with ∼93.3% capacitance retention after 10000 cycles at 5 A g−1. An asymmetric device which is assembled by using optimized CuCo2S4 electrode as positive electrode and activated carbon as negative electrode material is able to deliver an ultrahigh energy density of 50.56 Wh kg−1 at a power density of 4.6 kW kg−1, and remains 20.93 Wh kg−1 at a high power density of 22.5 kW kg−1, with ∼99% capacity retention after 10000 cycles. Based on the results above, the CuCo2S4 materials prepared by our method possess a considerable potential as electrode materials for supercapacitor applications.