Morphology-driven electrochemical properties of nickel-hydroxide and performance of asymmetric button-cell hybrid...

Nickel-hydroxides have garnered significant attention for energy storage applications owing to their unique interfacial characteristics and tunable structural properties. Despite this potential, precise morphological control of 3D/2D nanostructures remains a major challenge. In this study, we report a morphology-directed synthesis of nickel hydroxide (NH) nanostructures using two different halogen-containing precursors: ammonium iodide (AI) and ammonium chloride (ACl). The resulting AI-NH and ACl-NH samples exhibit distinct morphologies and physicochemical characteristics, influenced by the nature of the halide ions. Their electrochemical performance was systematically evaluated using both three-electrode and asymmetric button-cell configurations. Among the two electrodes, the ACl-NH electrode achieved a higher specific capacity of 795 C g^-1 at 1.5 A g^-1, compared to 601.5 C g^-1 for AI-NH, and retained 97% of its capacity over 6000 cycles at 24 A g^-1. This improvement is attributed to the increased surface area of ACl-NH (16.3 m² g^-1) versus AI-NH (9.58 m² g^-1). Furthermore, a asymmetric device assembled with AI-NH and ACl-NH electrodes delivered a specific capacitance of 106.5 F g^-1 at 1.5 A g^-1, an energy density of 37.8 Wh kg^-1 at a power density of 1975.3 W kg^-1, and maintained 78% capacity retention over 8500 cycles.