Building defect-rich oxide nanowires@graphene coaxial scrolls to boost high-rate capability, cycling durability and energy density for flexible Zn-ion batteries

Transition metal oxides with earth abundance and high theoretical capacity have received ever-growing interests as promising cathode materials for aqueous zinc-ion batteries (ZIBs). However, their semiconducting nature and poor conductivity lead to the kinetically sluggish rate and poor electrochemical reversibility. Herein, a novel defect-rich oxide nanowire filled graphene scrolls (denoted as DNGS) is introduced as a high-performance cathode for ZIBs. The 1D ultrathin oxide nanowires with defective nature are enwrapped in the center of the graphene scrolls, forming the core-shell coaxial scrolls. Benefitting from the highly conductive graphene network and 1D structured oxide with defect-rich structure, the DNGS hybrid scrolls achieve fast electron/ion transport, high electrochemical reversibility and superior energy storage capability. For the first time, the defect-rich vanadate oxide (V6O13-delta) is employed to construct the DNGS structure. The evolution of the DNGS structure is probed and the sequential mechanism based on the oriented growth, self-assembly and self-rolling process is disclosed. Both experimental and theoretical analyses demonstrate the significant increase in the electronic conductivity, ionic diffusion capability and electrochemical properties of the DNGS hybrid scrolls in comparison with the reference ones. The DNGS sample achieves ultrafast discharge capability and excellent deep cycling stability. Moreover, the flexible ZIBs based on the DNGS cathode display excellent high-rate long-term cycling stability (97% after 1000 cycles at alternative 13 and 4 A g(-1)) and admirable energy density (max. 231 mWh cm(-3)). Even under severe external deformation, the superior properties are well-retained which prove their high reliability. Therefore, this work not only provides a highly efficient structure to improve properties of oxides, but also propel the development of ZIBs for broadened applications.