Electrochemically triggered rational design of bismuth copper sulfide for wearable all-sulfide semi-solid-state supercapacitor with a wide operational potential window (1.8 V) and ultra-long life

There has been a growing need for supercapacitors (SCs) as a promising energy storage device with high energy and power densities. For this reason, electrodes with a wide operational potential window (OPW) and high capacity are desirable for energy storage. Previously, carbon-based electrodes were mostly used as a negative electrode in SCs, but their low capacity and narrow OPW hindered the performance of the SCs. Hence, a novel binder-free faradaic type bismuth copper sulfide (BCS) electrode has been synthesized in 600 s at room temperature via a simple and swift electrodeposition (ED) method. The effect of the Bi and Cu molar concentrations in the growth solution (Bi_xCu_3−xS₃) on its crystal structure and surface morphology is investigated during the ED process to further understand the synergistic benefits of Bi and Cu ions for enhanced electrochemical performance. The optimized BCS electrode exhibits excellent electrochemical properties with a wide OPW of 1.2 V and a specific capacity of 290 mA h g⁻¹. Additionally, nickel sulfide (NS) as a faradaic type positive electrode is synthesized via the ED. The BCS and NS electrodes are employed as negative and positive electrodes, respectively, to fabricate a novel gel electrolyte-based wearable all-sulfide semi-solid-state SC (ASSSC). The ASSSC device maintains ∼100% capacitance retention across the 40 000 charge-discharge cycles. Furthermore, two serially connected ASSSC devices are attached to the human fingers to power the electronic gadgets using various finger movements.