Synthesis of high-performance NiO/ZnO composite for asymmetric supercapacitors

The electrode material's design and structure greatly influence supercapacitor efficacy. This study employed a novel 2-step hydrothermal and calcination approach to synthesize NiO/ZnO composites with a hierarchical microflower-wrapped spherical structure. The effect of varying the Ni/Zn ratio was systematically investigated, and the optimized NiO/ZnO-3 electrode exhibited excellent electrochemical properties, including a low equivalent series resistance (R_s) of 0.73 Ω, a minimal charge-transfer resistance (R_ct) of 0.55 Ω, and a specific capacitance of 243 F g⁻¹ at 1 A g⁻¹. The electrode exhibited excellent cycling stability, retaining 87.2% of its capacitance after 5000 cycles at 15 A g⁻¹. The NiO/ZnO-3//AC asymmetric supercapacitor achieved 28.4 Wh kg⁻¹ energy density at 1170.1 W kg⁻¹ power density, retaining 114.8% capacitance after 10,000 cycles. This work highlights the synergistic effect of NiO/ZnO composites and introduces a scalable, cost-effective synthesis strategy that improves cycling stability and recyclability, advancing next-generation energy storage systems.