Freestanding, Hierarchical, and Porous Bilayered Na_xV₂O₅·nH₂O/rGO/CNT Composites as High-Performance Cathode Materials for Nonaqueous K-Ion Batteries and Aqueous Zinc-Ion Batteries

Rational design and convenient preparation of freestanding, hierarchical, and porous composites consisting of three-dimensional (3D) conductive carbon and low-dimension nanostructures with well-defined morphology and direct application as electrodes in rechargeable batteries are challenging. Herein, a freestanding, hierarchical, and porous composite composed of bilayered Na_xV₂O₅·nH₂O(NVO) nanobelts, carbon nanotubes (CNTs), and reduced graphene oxide (rGO) with a 3D cross-linked structure is prepared by simple one-pot hydrothermal self-assembly and vacuum filtration. The unique hierarchical nanoarchitecture of the hybrid one-dimensional (1D) (NVO nanobelts) and 3D (rGO/CNT) scaffold provides efficient pathways for ion/electron transportation as well as an elastic medium to buffer large volume change of the bilayered NVO nanobelts during cycling. The materials have excellent electrochemical properties as cathodes in the nonaqueous K-ion batteries (KIBs) and aqueous zinc-ion batteries (AZIBs). In the nonaqueous KIBs, the freestanding composite exhibits a high capacity of 119.9 mA h g^-1 at 0.1 A g^-1, a rate capability of 53.2 mA h g^-1 at 3 A g^-1, and a superior cycling stability of 59.7 mA h g^-1 at 0.5 mA g^-1 after 600 cycles. In the AZIBs, a capacity of 459.1 mA h g^-1 at 0.5 A g^-1, a rate capability of 352.5 mA h g^-1 at 10 A g^-1, and 83.1% retention after 1800 cycles at 10 A g^-1 are observed. Our results reveal the advantages of the 3D rGO/CNT platform for 1D vanadium-based oxide nanostructures and provide insights into the design and preparation of efficient cathode materials in high-performance AZIBs and nonaqueous KIBs.