Flexible Asymmetric Solid-State Supercapacitors by Highly Efficient 3D Nanostructured α-MnO₂ and h-CuS Electrodes

A simplistic and economical chemical way has been used to prepare highly efficient nanostructured, manganese oxide (α-MnO2) and hexagonal copper sulfide (h-CuS) electrodes directly on cheap and flexible stainless steel sheets. Flexible solid-state α-MnO2/flexible stainless steel (FSS)/polyvinyl alcohol (PVA)–LiClO4/h-CuS/FSS asymmetric supercapacitor (ASC) devices have been fabricated using PVA–LiClO4 gel electrolyte. Highly active surface areas of α-MnO2 (75 m2 g–1) and h-CuS (83 m2 g–1) electrodes contribute to more electrochemical reactions at the electrode and electrolyte interface. The ASC device has a prolonged working potential of +1.8 V and accomplishes a capacitance of 109.12 F g–1 at 5 mV s–1, energy density of 18.9 Wh kg–1, and long-term electrochemical cycling with a capacity retention of 93.3% after 5000 cycles. Additionally, ASC devices were successful in glowing seven white-light-emitting diodes for more than 7 min after 30 s of charging. Outstandingly, real practical demonstration suggests “ready-to-sell” products for industries.