Graphene Scroll‐Coated α‐MnO2 Nanowires as High‐Performance Cathode Materials for Aqueous Zn‐Ion Battery

The development of manganese dioxide as the cathode for aqueous Zn‐ion battery (ZIB) is limited by the rapid capacity fading and material dissolution. Here, a highly reversible aqueous ZIB using graphene scroll‐coated α‐MnO2 as the cathode is proposed. The graphene scroll is uniformly coated on the MnO2 nanowire with an average width of 5 nm, which increases the electrical conductivity of the MnO2 nanowire and relieves the dissolution of the cathode material during cycling. An energy density of 406.6 Wh kg−1 (382.2 mA h g−1) at 0.3 A g−1 can be reached, which is the highest specific energy value among all the cathode materials for aqueous Zn‐ion battery so far, and good long‐term cycling stability with 94% capacity retention after 3000 cycles at 3 A g−1 are achieved. Meanwhile, a two‐step intercalation mechanism that Zn ions first insert into the layers and then the tunnels of MnO2 framework is proved by in situ X‐ray diffraction, galvanostatic intermittent titration technique, and X‐ray photoelectron spectroscopy characterizations. The graphene scroll‐coated metallic oxide strategy can also bring intensive interests for other energy storage systems. Graphene scroll‐coated α‐MnO2 nanowires are studied as the cathode material for an aqueous Zn‐ion battery. The graphene layer increases the electrical conductivity of MnO2 nanowire and relieves the dissolution of the cathode material. An energy density of 406.6 Wh kg−1 can be reached, which is the highest specific energy value among all the cathode materials for aqueous Zn‐ion batteries so far.