Regeneration of waste Zn-MnO2 batteries: Value-added transformation to regenerate essential materials for sustainable battery manufacturing

Abstract

Zn-MnO2 batteries have a 3–5 year shelf life and make up 75 % of portable batteries. Disposing of spent batteries is a global issue and demand for MnO2 cathode material is growing 9.6 % annually, causing increased resource use and potential toxic metal leaching risk. Eco-efficient practices are needed to reduce environmental impact through recycling and reusing end-of-life products. Herein, electrolytic manganese dioxide (EMD) of spent Zn-MnO2 batteries was recycled using a thermochemical process where the structure of EMD was upgraded resulting in improving its electrochemical performance. The applicability of the recycled EMD as cathode into a new battery was explored by examining the discharge behaviour of the Zn-MnO2 cell made in KOH electrolyte and the results were compared with the performance of an original battery/EMD. In the recycled EMD cell, γ-MnO2 transformed to Zn2Mn7O8.H2O upon discharge (with a capacity of 213 mAh.g−1) and no Mn3O4 was observed, whereas in the original EMD, discharge resulted in the formation of mainly ZnMn5O4 and Mn3O4 (with a capacity of 175 mAh.g−1). The reversibility of the intercalation of cations into the structure of γ-MnO2 and their rechargeability was further examined via charge-discharge cycles using LiOH electrolyte where the recycled EMD exhibited enhanced behaviour. This indicates that in the recycled EMD, ZnMnO2 was able to revert to the original γ-MnO2, whereas in the original EMD, the formed Mn3O4 seemed to be irreversible resulting in the poor rechargeability behaviour of such batteries. Conclusively, the proposed method is a more efficient solution for reducing environmental impacts in value-added manufacturing due to its fewer steps compared to conventional techniques.