Strategic design of binary transition metal sulfides for superior asymmetric supercapacitors†

Abstract

Transition metal sulfides have emerged as promising materials for asymmetric supercapacitors due to their excellent electrochemical properties, including high specific capacitance and superior cycling stability. These characteristics offer significant potential for advancing energy storage technologies with improved performance and efficiency. In this study, a series of bimetallic sulfides were synthesized by systematically varying the nickel-to-cobalt ratio, starting from individual phases of NiS₂ and CoS₂. Among the prepared compositions, Ni_0.5Co_0.5S₂ demonstrated the most outstanding electrochemical behavior, achieving a high specific capacity of 1710 C g⁻¹ at a scan rate of 0.002 V s⁻¹. When employed as the anode material in an asymmetric supercapacitor device, it delivered an impressive energy density of 120 W h kg⁻¹ at a power density of 1020 W kg⁻¹. Notably, even at a high power density of 8510 W kg⁻¹, the device retained a substantial energy density of 36 W h kg⁻¹. Furthermore, the device exhibited excellent long-term cycling performance, maintaining 96% of its initial capacity after 4000 continuous charge–discharge cycles at a current density of 10 A g⁻¹. These findings highlight the strong potential of Ni_0.5Co_0.5S₂ as an efficient and durable electrode material for next-generation high-performance asymmetric supercapacitor systems.