Mitigation on self-discharge behaviors via morphological control of hierarchical Ni-sulfides/Ni-oxides electrodes for long-life-supercapacitors.

• Heterostructure of Nickel Sulfides on NiO oxides by the hydrothermal and SILAR process. • Morphological control via SILAR overcoating tuning the electrochemical performance of the nanocomposite of NS/NO. • SILAR overcoating modulates nanostructure of CO facilitating short diffusion paths and abundant electroactive sites. • The GCD, voltage holding and self-discharge study performed on both NS20/NO and NO SCs for 4 cycles. • This study proposes the behind mechanism self-discharge and the current leakage during voltage holding revealed the sound architecture of SC assembly. • The symmetric supercapacitor showed a high energy density 148.20 W h kg⁻¹ and power density of 3500 W kg⁻¹. • LED demonstration powered by NS20/NO and NO based SSC shows an improvement of 35% in LED lit timing. To cope up with the sustainable energy storage goals for supercapacitors (SCs), the self-discharge in SC electrodes is a significant hurdle, and thereby, nickel sulfide (NS) with high conductivity is adopted as a test vehicle for understanding the morphological evolution effects for long-life SCs. Herein, honeycomb-like NS is hierarchically formed over hydrothermally grown nickel oxide (NO) via successive ionic layer adsorption reaction (SILAR) method. Their heterostructure shows a fivefold improvement in specific capacitance from 348 F g⁻¹ to 2077 F g⁻¹ at 1 mV s⁻¹ over bare NO. Furthermore, the remarkable upliftment of capacitance retention is achieved from 60.7% to 92.3% even after 3000 cycles via morphological control of NS/NO hetero-structure with the help of highly conductive NS. More importantly, the self-discharge behaviors and synergistic role of leakage current associated with morphological evolution via NS overcoating are studied in detail. In particular, the self-discharge mitigation from 45% (NO) to 35% (NS20/NO) due to the NS/NO heterostructure and the behind mechanism are ascribed to the activated-controlled Faradaic reaction coupled with a charge redistribution. This study emphasizes the potential importance of composite heterostructure by tuning the electrical conductivity and morphological adjustment NO via consecutive overcoating of NS through SILAR as a novel strategy. This enhances charge storage, redox kinetics, and the mitigation of self-discharge properties of the active electrode materials. For practical validation on sustainable energy storage, NS20/NO supercapacitors illuminate the LED for 35% longer than NO after one-time charging, potentially beneficial for the next generation SCs. [ABSTRACT FROM AUTHOR]