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.