Inspired by the recycling approach of electronic waste, within this research paper, we extracted exhausted materials from spent primary zinc batteries and then annealed them in a modified condition, forming a ZnMn2O4/ C composite with a uniform nanoparticles’ porous morphology. The produced material has been examined as a supercapacitor active one, which showed promising electrochemical properties for supercapacitor application. At a current density of 3 A g− 1, it exerted a comparatively significant capacitance of 1696.88 F g− 1 along with a capacity of 807 C g− 1. Furthermore, the fabrication of a flexible all-solid-state symmetric supercapacitor prototype has been accomplished. It exhibited promising initial results that carried a specific energy of 76.75 Wh kg− 1 at a specific power of 333.86 W kg− 1. After 3000 cycles, it maintained an acceptable capacity. Thus, this eco-friendly approach can successfully convert the spent battery material to new value-added materials for supercapacitors in the clean energy area.