A simple and chemical-free recycled carbon-ZnMn2O4 powder (composite) from the spent Zn-carbon batteries is proposed as an effective active material for the supercapacitor. This approach may amplify the economic and environmental benefits of the recycling process. We also synthesized the spherical MnOx nanoparticles by the calcination followed by the chemical treatment. Recycled composite and the MnOx nanoparticles were comprehensively characterized. Symmetrical supercapacitors with the composite and the MnOx nanoparticles show specific capacitances of 118 F g-1 and 88 F g-1 at 0.1 A g-1, respectively. Also, the supercapacitor with the composite offers a specific energy of 8.0Whkg-1 at 0.1A g-1 while 4.3Whkg-1 is obtained for MnOx nanoparticles. The stable cell potential limits of 1.4 V and 1.2 V were established for the supercapacitors of the composite and MnOx nanoparticles with the capacitance retention of 83% and 96%, respectively at the end of 100,000 cycles at 2.5Ag-1. Also, the excellent energy efficiencies of 80% and 72% with the coulombic efficiency of 100% are estimated for the supercapacitors of the composite and the MnOx nanoparticles, respectively. Finally, in situ gas analysis of the symmetrical supercapacitors are carried out using the differential electrochemical mass spectrometry. The proposed approach may be more economical and the environmentally benign recycling of spent Zn-carbon battery for circular economy and sustainability.