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 x V 2 O 5 •nH 2 O(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.

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Transition-metal oxides have attracted much attention as promising anode materials, owing to high theoretical specific capacity for lithium-ion batteries (LIBs). However, rapid performance degradation derived from poor electrical conductivity and drastic volume changes during the repeated lithium insertion/ extraction processes has limited their practical applications. In this work, we design and prepare pomegranate-like microspheres of nano-sized MnO particles with gaps among them as the core and porous carbon as the shell (designated as PCMS@MnO) by using a facile three-step process. In such unique PCMS@MnO, the porous carbon shell from phenolic resin is beneficial for the electronic conductivity and wettability, whereas the nano-sized MnO particles with gaps among them confined in the porous carbon shell can effectively prevent aggregation and pulverization of active materials. As an anode material for LIBs, the PCMS@MnO with a carbon content of about 12 wt % exhibits remarkably high reversible capability (935 mAh g À 1 at 100 mA g À 1 ), outstanding rate performance, and superior cycling stability (527 mAh g À 1 of 2000 mA g À 1 after 2000 cycles). Our results suggest a great potential of pomegranate-like transition-metal oxide-based composites as anode materials in high-performance LIBs.

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