Ultrathin MnO2 nanoflakes grown on N-doped hollow carbon spheres for high-performance aqueous zinc ion batteries

The use of MnO2 as a promising cathode material for aqueous zinc ion batteries (AZIBs) remains challenging, because its inherent poor electrical conductivity and huge volume changes lead to a fast capacity decay, short cycle life, and sluggish electrode kinetics. In this study, ultrathin MnO2 nanoflakes grown on N-doped hollow carbon spheres (defined as MnO2-NHCSs) were prepared via a simple solution-phase route and subsequent hydrothermal process, and then evaluated for their potential as a cathode for AZIBs. Ultrathin MnO2 nanoflakes decorated on NHCSs endow the overall electrode with abundant exposed active sites and excellent electrical conductivity, which could buffer the volumetric expansion and facilitate the charge-transfer kinetics. Owing to these favorable structural characteristics, the as-synthesized MnO2-NHCS composite can display a high discharge capacity of 349 mA h g(-1) at 0.1 A g(-1) after 80 cycles. Significantly, ultra-stable long-term cycling performance of 100 mA h g(-1) with a superior capacity retention of 78.7% is achieved after 2000 cycles at 2.0 A g(-1). Such notable electrochemical properties of MnO2-NHCSs are demonstrated to be superior to that of pure MnO2 hollow spheres (MnO2-HSs) and other previously reported manganese-based oxide cathodes, which is promising for practical applications.