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.