Unraveling the Role of Nitrogen‐Doped Carbon Nanowires Incorporated with MnO2 Nanosheets as High Performance Cathode for Zinc‐Ion Batteries

Abstract

Manganese‐based cathode materials are considered as a promising candidate for rechargeable aqueous zinc‐ion batteries (ZIBs). Suffering from poor conductive and limited structure tolerance, various carbon matrix, especially N‐doped carbon, were employed to incorporate with MnO2 for greatly promoted electrochemical performances. However, the related underlying mechanism is still unknown, which is unfavorable to guide the design of high performance electrode. Herein, by incorporating layered MnO2 with N‐doped carbon nanowires, a free‐standing cathode with hierarchical core‐shell structure (denoted as MnO2@NC) is prepared. Benefiting from the N‐doped carbon and rational architecture, the MnO2@NC electrode shows an enhanced specific capacity (325 mAh g−1 at 0.1 A g−1) and rate performance (90 mAh g−1 at 2 A g−1), as well as improved cycling stability. Furthermore, the performance improvement mechanism of MnO2 incorporated by N‐doped carbon is investigated by X‐ray photoelectron spectroscopy (XPS), Raman spectrums and density functional theory (DFT) calculation. The N atom elongates the Mn‐O bond and reduces the valence of Mn4+ ion in MnO2 crystal by delocalizing its electron clouds. Thus, the electrostatic repulsion will be weakened when Zn2+/H+ insert into the host MnO2 lattices, which is profitable to more cation insertion and faster ion transfer kinetics for higher capacity and rate capability. This work elucidates a fundamental understanding of the functions of N‐doped carbon in composite materials and shed light on a practical pathway to optimize other electrode materials.