Sodium ion-stabilized 2 × 4 tunnel manganese oxide nanorods as cathodes for high-performance aqueous zinc-ion batteries

Manganese dioxide nanorods (Na0.4MnO2) with a typical 2 × 4 tunnel structure are successfully synthesized by the simple hydrothermal method in the presence of 5 M NaCl. The nanorods are about 30 nm in diameter. ZIBs (zinc-ion batteries) with Na0.4MnO2 display a specific capacity of 274.6 mA h g−1 at 0.2 A g−1 and have a high reversible capacity of 182.6 mA h g−1 after 1400 charge–discharge cycles at 1 A g−1 with a capacity retention of 96.5%. The unique morphology endows abundant electrochemical active sites and facile ion diffusion kinetics, which contributes to high specific capacity and stability. Both Zn2+ and H+ are inserted/extracted during the discharging/charging processes, and the crystalline structure and morphology of the nanorods do not change after repetitive cycling. The Na0.4MnO2 with the 2 × 4 tunnel structure is a promising candidate as the electrode material for ZIBs.