A Structurally Stable α-MnO2 nanorod Cathode for Enhanced Reversible Divalent Zinc Storage

In this study, a nanorod-type α-MnO₂ cathode prepared by a facile hydrothermal reaction was utilized for rechargeable aqueous zinc-ion battery (ZIB) applications. Electron microscopy studies revealed rod-type particles with approximately 20 and 200 nm of width and length, respectively. When tested for zinc storage properties, the nanorod cathode exhibited an initial discharge capacity of 176.8 mAh/g at a current density of 83 mA/g and demonstrated nearly 100% Coulombic efficiencies under prolonged cycling. Further, rate performance measurements revealed that specific capacities of 43.33 and 31.48 mAh/g were attained at current densities as high as 1333 and 1666 mA/g. Ex-situ XAS investigations confirmed the reversibility of electrochemical Zn-insertion into the a-MnO₂ electrode. Moreover, a combination of ex-situ synchrotron XRD studies, visualization and pattern-fitting software programs not only established the electrochemical Zn-insertion into the host a-MnO₂ structure but also indicated that the unit cell volume of the [2x2] tunnels in the a-MnO₂ host expands by approximately 3.12% during Zn-insertion. The present study thus paves the way for further development of aqueous ZIB as an ideal energy storage system due to its excellent safety and reliability.