Enhanced Energy Density of All-Solid-State Asymmetric Supercapacitors Based on Morphologically Tuned Hydrous Cobalt Phosphate Electrode as Cathode Material

In the present investigation, microflowers-like hydrous cobalt phosphate is prepared via a facile single-step hydrothermal method on stainless steel substrate. The microflowers-like morphology of hydrous cobalt phosphate thin film consists of microplates and further microplates converted to flakes by means of a change in length, width, and thickness with urea variation. Hydrous cobalt phosphate thin film electrode demonstrates a high specific capacitance of 800 F g–1 at 2 mA cm–2 with 33.62 Wh kg–1 energy density and 3.12 kW kg–1 power density. By taking advantage of hydrous cobalt phosphate thin film (as a cathode electrode) and copper sulfide thin film (as an anode electrode), the asymmetric devices (aqueous/all-solid-state) are fabricated. Aqueous asymmetric device shows a high specific capacitance of 163 F g–1 at 2 mA cm–2 with an energy density of 58.12 Wh kg–1 and power density of 3.52 kW kg–1. Moreover, the all-solid-state asymmetric supercapacitor device delivers a high specific capacitance of 70 F g–1 at 2 mA cm–2 with 24.91 Wh kg–1 energy density and 2.63 kW kg–1 power density in PVA–KOH gel electrolyte. The long-term cyclic stability (94% after 3000 cycles) and actual practical demonstration (lightning 65 red LEDs) suggest an industrial application of the all-solid-state asymmetric device.