Upcycling zinc-carbon batteries for tunable manganese dioxides and zinc electrolytes in rechargeable batteries.

A key challenge in battery recycling is the development of processes that can transform waste materials into value-added electrode materials for use in rechargeable batteries. Here, we demonstrate a novel upcycling approach of spent zinc-carbon batteries to enable phase-controlled synthesis of MnO2 polymorphs (α-, γ-, β-, and λ-MnO2) as cathode materials in rechargeable zinc-ion batteries. Through manual dismantling under controlled condition and selective separation, manganese was recovered and converted into high-purity MnO2 polymorphs using simple precipitation and hydrothermal methods under oxidizing acidic conditions. Their distinct crystal structures and morphologies were characterized using XRD, SEM, and TEM. The BET surface area of MnO2 polymorphs was found to be 70.51 m2/g for α-phase, 57.64 m2/g for γ-phase, 8.25 m2/g for β-phase, and 23.53 m2/g for λ-phase. All MnO2 polymorphs exhibited similar electrochemical behavior during discharge, delivering comparable specific capacity ranging from 200-300 mAh/g for the tunnel-type structures and approximately 47 mAh/g for the spinel-type structure. Moreover, the storage mechanism of upcycled α-MnO2 electrode assembled with electrolytes obtained from the leaching solution was associated with the reversible co-intercalation and extraction of H+ and Zn2+ ions. Notably, the presence of Mn2+ in the recycled electrolyte can significantly enhance the structural stability and cycling performance of α-MnO2 electrode with 63.47 % capacity retention over 200 cycles. This current work demonstrates a novel approach of material upcycling from spent primary batteries toward phase-controlled synthesis of pure MnO2 polymorphs with promising electrochemical performance for rechargeable zinc-ion batteries.