Proton Insertion Promoted a Polyfurfural/MnO2 Nanocomposite Cathode for a Rechargeable Aqueous Zn–MnO2 Battery

Rechargeable aqueous Zn–MnO2 batteries using a mild electrolyte have attracted considerable interest because of their high output voltage, high safety, low cost, and environmental friendliness. However, poor cycling stability remains a significant issue for their applications. Equally, the energy storage mechanism involved is still controversial thus far. Herein, porous polyfurfural/MnO2 (PFM) nanocomposites are prepared via a facile one-step method. When tested in a rechargeable aqueous Zn–MnO2 cell, the PFM nanocomposites deliver high specific capacity, considerable rate performance, and excellent long-term cyclic stability. Based on the experimental results, the role of the hydrated basic zinc sulfate layer being linked to the cycling stability of the aqueous rechargeable zinc-ion batteries is revealed. The mechanistic details of the insertion reaction based on the H+ ion storage mechanism are proposed, which plays a crucial role in maintaining the cycling performance of the rechargeable aqueous Zn–MnO2 cell. We expect that this work will provide an insight into the energy storage mechanism of MnO2 in aqueous systems and pave the way for the design of long-term cycling stable electrode materials for rechargeable aqueous Zn–MnO2 batteries.