Aqueous Na-ion capacitor with CuS graphene composite in symmetric and asymmetric configurations

Abstract

Sodium ion capacitors (NICs) play a significant role in providing high energy and power densities in a single device at low cost. However, most of the work is focused on exploring the host material to store Na⁺ ions. This manuscript explores metal chalcogenide for NICs applications. Here, we successfully synthesized a pseudocapacitive copper sulphide (CuS) and its composite with graphene (CuS-G) electrode by a simple chemical route to store Na⁺ ions. A moderate crystallite size of 25 nm is found for CuS with spherical morphology. Electrochemical studies were performed in an aqueous medium for each of the two and three-electrode systems. The specific capacitances of 87 and 13 F g⁻¹ were obtained at 0.5 A g⁻¹ for the symmetric and asymmetric devices, respectively. For the asymmetric devices, an energy density of 2.6 W h kg⁻¹ (maximum) at a power density of 246 W kg⁻¹ was obtained and reduced to 1 W h kg⁻¹ at the highest power density of 2980 W kg⁻¹. The symmetric device shows a maximum energy density of 30 W h kg⁻¹ at a power density of 380 W kg⁻¹, which is reduced to 4 W h kg⁻¹ at the highest power density of 4224 W kg⁻¹. The cyclic stability for each device was performed up to 1000 cycles. A Coulombic efficiency of 100% is observed for both symmetric and asymmetric devices.