Synergizing manganese oxide on hydrothermally reduced graphene oxide for high-performance cathodes in green zinc batteries

A broad tunnelled manganese oxide(a-MnO₂) as cathode material for the zinc ion batteries (ZIBs) is energy efficient, budget friendly, naturally abundant, safe, and greener energy source. The ZIBs can fulfil future electrical energy storage demands and efficacious candidates to compete with other metal ion batteries. However, the inferior conductivity of a-MnO₂ is a limitation which degrade the electrochemical performance for the practical application. Reduced graphene oxide is known for its excellent conductivity. When wrapped with a-MnO₂, it minimizes volume expansion caused due to intercalation process, adding stability and conductivity to structure. We studied impact of tuning reaction time for hydrothermally wrapped a-MnO₂ on reduced graphene oxide (HMGO) as cathode material in the ZIBs. The structural and morphological features of HMGO was investigated using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Nitrogen adsorption-desorption isotherms were used to investigate the Brunauer-Emmett-Teller (BET) surface area and pore structure. A series of samples were prepared with hydrothermal reaction time of 4, 6, and 8 hours, respectively. The HMGO sample for hydrothermal reaction time of 6 hour (HMGO₆) demonstrates attractive capacity of 333 mAh/g at the current density 200 mA/g. HMGO₆ has admirable cycling stability of 93% and coulombic efficiency of 92.5% for 500 cycles at 500 mA/g. It also demonstrates the remarkable energy density of 273.32 Wh/kg at the power density of 0.79 W/kg using HMGO ₆/Zn battery. (author)