Integrated electrode-electrolyte optimization to fabricate pinewood-derived carbon-permeated CoNi3S4(P) hybrid nanocomposites as redox-rich electrode materials for ultra-high energy density hybrid supercapacitors

Aqueous supercapacitors are considered feasible energy storage devices due to their high safety, nontoxicity, and affordability. However, real-world applications are hindered by the long-term cycling stability of the electrode materials. This study demonstrates the rational design of hybrid CoNi 3 S 4 (P)@pine wood-derived carbon (PWC) nanocomposite (CNSP@PWC), which operates effectively in hybrid electrolytes. The inner core of Co/Ni nanoparticles , combined with the nanostructured outer surface of the carbon materials, synergistically enhances conductivity and accelerates charge transfer. The hybrid electrolyte-electrode design has been strategically developed to facilitate efficient cation desorption, thereby preventing anode dissolution and structural distortion. The hybrid nanocomposite attains a high capacity of 801 C/g at a current density of 0.5 A/g when tested in a hybrid electrolyte solution containing 1.0 M potassium hydroxide (KOH) and sodium sulfate (Na 2 SO 4 ), which outperforms its capacity in individual electrolytes. Moreover, the hybrid supercapacitor device exhibits excellent rate capability, achieving an ultra-high energy density of 141 Wh/kg at a current density of 0.5 A/g and high power density of 18000 W/kg at current density of 15 A/g. With a wide potential window (2.4 V) and impressive capacity retention of 90 % at 10 A/g for 5000 cycles, the device demonstrates an advancement in supercapacitor design and exceptional performance. The present study develops a high-performing hybrid nanocomposite electrode material integrated with an optimized electrolyte to meet the demands of practical energy storage devices. • Porous carbon nanostructure (CNSP@PWC) provides more active sites and fast redox reactions. • Hybrid electrolyte electrode design is developed to facilitate efficient cation desorption. • Hybrid nanocomposite in a hybrid (KOH + Na 2 SO 4 ) electrolyte results in a higher capacity. • HSC device exhibits ultra high energy density (141 Wh/kg) and power density (18,000 W/kg).