Synergistic dual-potential pseudocapacitance of in situ grown NixSy-CuS nanospheres on laser-induced graphene for next-generation wearable electronics

Wearable electronic textiles are promising platforms for integrating flexible energy-storage devices into daily life. In this study, a high-performance nickel and copper sulfides nanostructure was directly grown on laser-induced graphene (LIG) through a simple binder-free process for flexible interdigitated micro-supercapacitor (FIMS) and flexible asymmetric sandwich supercapacitor (FASS) applications. The porous LIG network enabled in situ growth of Ni x S y -CuS nanospheres without hydrothermal treatment, providing abundant electroactive sites and rapid charge transport. Electrochemical evaluation showed excellent performance in both positive and negative potential windows, where NiS and Ni 3 S 2 enhanced redox activity at positive potentials while CuS improved electrochemical behavior at negative potentials. As a result, the Ni x S y -CuS@LIG electrode achieved high specific capacitances of 75.4 and 163.2 mF cm −2 in positive and negative regions, respectively. Dunn's and Trasatti's analyses confirmed dominant pseudocapacitive charge-storage behavior. The fabricated FIMS device exhibited long-term stability, retaining 86.4% of its initial capacitance with 95.92% coulombic efficiency after 3000 cycles at 0.6 mA cm −2 , and successfully powered LEDs and small electronic devices. Furthermore, the FASS device delivered an energy density of 7.3 mWh cm −2 and a power density of 303.4 mW cm −2 , demonstrating strong potential for wearable electronics.