Graphene-Composite δ-MnO2 Nanoflower Cathode Enhances Zinc Storage Performance and Cycling Stability in Aqueous Zinc Ion Batteries

MnO 2 is the most promising cathode material for aqueous zinc ion batteries (AZIBs), but poor conductivity, structural instability, and slow Zn 2+ kinetics in MnO 2 -based AZIBs still limit their practical use. Here, we present the introduction of graphene (Gr) into δ-MnO 2 with a layered structure designed for AZIBs to understand the effect of carbon materials on the electrochemical behavior of δ-MnO 2 cathodes. Nanoflower-structured δ-MnO 2 composites with graphene were fabricated via a one-step hydrothermal synthesis method. Owing to the incorporation of Gr, the cycling stability, rate performance, and reversibility of δ-MnO 2 have been significantly enhanced. The results show that at a current density of 0.5 A g − 1 , the δ-MnO 2 -1.5 h/Gr electrode exhibits a specific capacity of 125 mAh g − 1 with a capacity retention of 53.4% and a high Coulombic efficiency of 99.2%. At a higher current density of 1 A g − 1 , this electrode delivers a specific capacity of 142.5 mAh g − 1 after 1000 cycles, substantially higher than that of the δ-MnO 2 -1.5 h electrode. In addition, electrochemical data show that δ-MnO 2 -1.5 h/Gr possesses a higher pseudo-capacitance percentage and best rate performance. This study confirms that incorporating carbon materials is an effective strategy for enhancing the energy storage performance of δ-MnO 2 in AZIBs and understanding its charge-discharge mechanism. Graphical The incorporation of graphene (Gr) improved the cycling stability, rate capability, and reversibility of δ-MnO2. δ-MnO2/Gr possessed higher ion diffusion rates and higher pseudo-capacitance occupancy, and exhibited the best rate performance. Thus, improving the zinc storage performance and cycling stability of zinc ion water batteries.