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

Abstract

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.