High Interspace-Layer Manganese Selenide Nanorods as a High-Performance Cathode for Aqueous Zinc-Ion Batteries

This study presents a low-cost and straightforward α-MnSe-nanorod (NR) cathode active material (CAM) with superior function in rechargeable aqueous zinc-ion batteries (AZIBs). The facile two-dimensional Zn2+ transport channels, tunnel type, and layered structure render such CAMs as the potential cathode materials embedded in AZIBs. However, their practical usage has been limited by either poor cycling stability or low capacity. We are the first to develop an α-MnSe-NR cathode synthesized by a facile hydrothermal method with lengths up to 100 nm and diameters around 30 nm for ZIBs, featuring a large tunnel diameter of 6.07 Å and an interlayer spacing of 0.91 nm. During the in situ electrochemical activation process, the α-MnSe-NR is electrochemically oxidized to MnSe (MnSe-EO). This reflects the higher Zn2+ storage capacity in MnSe-EO cathodes. Besides, the higher pseudocapacitive performance of MnSe-EO compared to the α-MnO2 gives rise to a much higher rate of charge/discharge. The developed cathode presents a high reversible capacity (309 mA h g–1) and durable cyclability by 83.4% capacity retention after 1000 cycles at 5 A g–1. In addition, a detailed study of the coinsertion process of hydrated H+/Zn2+ in MnSe-EO was conducted, clarifying the self-regulating mechanism of electrolyte-involved production of flake-like zinc hydrogen sulfate. The preferential embedding process and low adsorption energy of zinc ions were confirmed by density functional theory analysis, which may further enhance Zn2+ migration and adsorption abilities in the cathode structure, which is primarily responsible for the corresponding superior performance. Electrochemical measurements confirmed the favorable pseudocapacitive functions and the superior Zn2+ migration kinetics.