Freestanding, Hierarchical, and Porous Bilayered NaxV2O5•nH2O/rGO-CNT Composite as High-Performance Cathode Materials for Nonaqueous K-ion Batteries and Aqueous Zinc-ion Batteries.

The rational design and convenient fabrication 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 NaxV2O5•nH2O(NVO) nanobelts, carbon nanotubes (CNT), 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 1D (NVO nanobelts) and 3D (CNT-rGO) scaffold provide efficient pathways for ion/electron transportation as well as a robust buffer to accommodate the 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 mAhg-1 at 100 mAg-1, rate capability of 53.2 mAhg-1 at 3000 mAg-1, and superior cycling stability of 59.7 mAhg-1 at 500 mAg-1 after 600 cycles. In the AZIBs, a capacity of 459.1 mAhg-1 at 0.5 Ag-1, rate capability of 352.5 mAhg-1 at 10 Ag-1, and 83.1% retention after 1800 cycles at 10Ag-1 are observed. Our results reveal the advantages of the 3D CNT-rGO platform for 1D vanadium-based oxide nanostructures and provide insights into the design and fabrication of efficient cathode materials in high-performance AZIBs and nonaqueous KIBs.