Strongly coupled zinc manganate nanodots and graphene composite as an advanced cathode material for aqueous zinc ion batteries

Manganese-based oxides with high capacity and moderate operation voltage have been extensively studied as promising cathode materials for aqueous zinc ion batteries (ZIBs). However, the inherent poor electrical conductivity, sluggish reaction kinetics, huge volume expansion and dissolution of manganese species in electrolyte greatly restrict their practical applications. Herein, ultrasmall ZnMn2O4 nanodots uniformly anchored on reduced graphene oxide with strong interfacial interaction (ZnMn2O4 NDs/rGO composite) is synthesized. Compared with the pure ZnMn2O4 microspheres, the ZnMn2O4 NDs/rGO composite displays a much higher discharge capacity of 207.6 mA h g(-1) at a current density of 0.2 A g(-1), as well as better rate capability and long-term cycling stability. Impressively, the aqueous Zn//ZnMn2O4 NDs/rGO battery exhibits a high energy density of 266 W h kg(-1) at a power density of 137 W kg(-1), indicating great potential for practical applications. The excellent performance could be attributed to the abundant active sites, shortened ion diffusion pathway, improved electrical conductivity and good structure stability. Furthermore, electrochemical analyses reveal that favorable reaction kinetics towards efficient zinc ion storage is achieved in the composite. The present work might shed light on the rational design and synthesis of advanced strongly coupled graphene based composites as cathode materials for aqueous ZIBs.