One of the most worrying environmental issues affecting all forms of life, the economy, and natural ecosystems globally is the accumulation of polyethylene (PE) plastic garbage. Creating peaceful and environmentally friendly alternatives to conventional disposal techniques, like transforming plastic waste into cherished carbonaceous nanomaterials, is of utmost importance considering this threat. The current study carefully employed a cleaner upcycling technique to create carbon-based nanomaterials (CNMs) for supercapacitors. Using solvothermal/hydrothermal synthetic techniques, the PE waste was transformed into CNMs used in energy storage supercapacitors application. With an energy density of 21.6 W h kg−1 and a current density of 0.25 A g−1, the electrochemical test showed a specific capacitance of 155.5 F g−1. Additionally, the materials demonstrated 98.5% capacitance retention after 9000 cycles at a constant current density of 1.0 A g−1.