Facile synthesis of Cu_1.96S nanoparticles for enhanced energy density in flexible all-solid-state asymmetric supercapacitors

The exploration of copper sulfide materials have attracted significant attention for flexible all-solid-state asymmetric supercapacitor (FASC) application due to their advantages of cheapness and low toxicity. In this paper, three types of Cu_1.96S samples with different morphologies were successfully fabricated by a facile hydrothermal method. The obtained Cu_1.96S-12 nanoparticles (NPs) product exhibits a higher specific capacitance of 1928.6 F/g at a current density of 1 A/g, better rate capability (retain 79.2% of initial capacitance at the current density of 5 A/g) as well as much excellent cycling performance with 90.1% retention after 1000 cycles than those of Cu_1.96S-6 and Cu_1.96S-15 samples, which can be attributed to the unique structural properties (nanoparticle structure and well-developed mesoporous structure) and large specific surface area. Hence, a FASC device with high energy density has been successfully assembled using Cu_1.96S-12 NPs as the positive electrode and active carbon (AC) as the negative electrode. The Cu_1.96S-12//AC with an output voltage of 1.5 V shows superior electrochemical performance such as a high specific capacitance of 9.33 F/g at 1 A/g, excellent cyclability of 88.8% retention after 1000 charge/discharge cycles at a constant current density of 10 A/g, remarkable rate performance (~ 91.1% retention is obtained), outstanding flexibility (~ 99.1% specific capacitance maintained at the angle of 360°) and a high energy density of 10.50 Wh/kg compared to other recently reported data. This work provides a new insights into the actual application of Cu_1.96S cathode materials for FASC devices and other energy storage devices.