Synergistic vacancy and sulfur modulation in Co₂CuS₄ nanorods for enhanced symmetric supercapacitor performance

The rapid proliferation of portable and high-power electronic devices has intensified the pursuit of advanced energy storage systems with high energy and power densities. Supercapacitors bridge this performance gap; however, their limited energy density remains a major challenge. Herein, a dual-engineering strategy is proposed to construct highly efficient symmetric supercapacitors based on Co₂CuS₄ nanorods derived from oxygen-deficient Co₂CuO₄ (O_V-Co₂CuO₄). The combined effects of oxygen vacancy creation and sulfur substitution synergistically tailor the electronic configuration, promote redox kinetics, enhance electrical conductivity, and increase the density of electroactive sites. As a result, the optimized O_V-Co₂CuS₄ electrode delivers an outstanding specific capacitance of 2293 F/g at 1 A/g and retains 62% of initial capacitance at 10 A/g. The assembled symmetric device achieves an energy density of 80.41 Wh/kg at 1.8 kW/kg and maintains 50.05 Wh/kg even at tenfold higher power, alongside excellent cycling stability (>94% after 10,000 cycles). This work demonstrates that the simultaneous tuning of lattice vacancies and anion composition provides a rational pathway to bridge the energy-power trade-off in supercapacitors, paving the way for scalable, binder-free energy storage devices.