Manipulating intercalation-extraction mechanisms in structurally modulated δ-MnO2 nanowires for high-performance aqueous zinc-ion batteries

Abstract

Rechargeable aqueous zinc–ion batteries (ZIBs) have attracted wide attention recently because of their low cost, high safety, and environmental friendliness. However, manganese–based materials always suffer from irreversible structural transformation and sluggish reaction kinetics, resulting in low capacity and poor cycling stability, which hinders their practical application in large–scale energy storage. Herein, we demonstrate a structural modulation strategy to manipulate the electrochemical reaction mechanism in layered δ–MnO2 via Cu2+ intercalation. A favorable H+/Zn2+ intercalation–extraction mechanism is identified in structurally modulated δ–MnO2 electrode after the reversible Zn2+ intercalation and H+ conversion reaction in the initial several cycles, which is thoroughly investigated and demonstrated through multiple analytical means. The resulted δ–MnO2 cathodes deliver rapid and reversible Zn2+ storage, with a high reversible capacity of 398.2 mAh g−1 at 0.1 A g−1 and 90.1% capacity retention after 700 cycles at 5 A g−1. Further ex–situ characterization demonstrates the rapid and reversible H+/Zn2+ storage in the structurally modulated δ–MnO2 cathodes. Density functional theory calculations reveal Cu2+ intercalation in δ–MnO2 effectively enhances the structural stability of δ–MnO2 via the strong ionic bonds bonded with oxygen atoms, and also optimizes electronic bandgap and ion/charge state of δ–MnO2, thus attributing favorable ion intercalation–extraction mechanisms. This structural modulation strategy provides a new gateway to the development of robust–structured cathode materials by manipulating the electrochemical reaction mechanisms in electrode materials for ZIBs.