2D nanocoin structure with binder-free CuS electrode for flexible symmetric solid-state supercapacitors

Copper-based chalcogenides are a popular choice for supercapacitor electrodes because of their unique electrochemical characteristics with ease of manufacture. We present a versatile, bendable solid-state device that incorporates a pliable polyvinyl alcohol (PVA) - Potassium hydroxide (KOH) membrane and copper sulphide (CuS) nanocoin electrodes on a stainless-steel current collector. One-pot colloidal synthesis is used to produce the CuS nanocoins, and a straightforward binder-free dip-and-dry technique is used to deposit them onto a flexible stainless-steel substrate. These nanocoins, with nanometric thickness (7.48 ± 1.49 nm) and lateral size (42.86 ± 1.14 nm), exhibit a highly crystalline structure with a promising electrochemically dynamic surface area of 551 m²/g that enhances charge storage, promoting pseudocapacitive behavior. This results in a high specific capacitance of 1159 F/g (811 mF/cm²) at a scan rate of 2 mV/s in a 1 M KOH electrolyte solution. Furthermore, we used the Trasatti approach to examine the different contributions that diffusion-limited and surface-controlled processes gave to the electrode's total charge storage capacity. We developed a flexible PVA-KOH membrane and employed it as a solid-state electrolyte to improve flexibility and device performance. This unique combination enables the flexible symmetric solid-state device to achieve an energy density of 11 Wh/kg and a power density of 900 W/kg, with a coulombic efficiency of 98 %. The device demonstrates remarkable long-term cyclic stability, retaining 89 % of its initial capacitance even after 10,000 charge-discharge cycles. The device's remarkable flexibility without performance loss further emphasizes its potential for energy storage and flexible electronics applications.