Hollow-porous nanospheres of ZnMn2O4 spinel: A high energy density cathode for rechargeable aqueous battery

Well-controlled hollow-porous nanostructures can provide enhanced charge storage capacity owing to the rapid diffusion of electrolyte ions into their interior. However, interface engineering of stable hollow-porous nanostructures with reversible faradaic reactions for efficient energy conversion/storage devices is still a challenge. Herein, we report solvothermal synthesis of spinel ZnMn2O4 with a hollow-porous spherical (ZMOHS) morphology. The formation mechanism of such a hierarchical nanostructure has been discussed. The ZMOHS exhibits a specific capacity of ~187 mAh g−1 at a current density of 2 A g−1 when tested as a faradaic electrode (vs Pt) for a rechargeable aqueous battery (RAB) in alkaline electrolyte. Furthermore, a full cell RAB constituting of ZMOHS//activated carbon (AC) demonstrates energy and power densities of ~215.7 Wh Kg−1 and ~1184.5 W kg−1 respectively, with ultra-long cycling stability (~106% capacitance retention after 10,000 cycles), making it a very promising material for next-generation energy storage device applications.