In situ construction of ball-in-ball structured porous vanadium pentoxide intertwined with carbon fibers induces superior electronic/ionic transport dynamics for aqueous zinc-ion batteries

Using V2O5 as an aqueous zinc-ion battery (ZIB) cathode has major drawbacks, including inferior electrode/electrolyte contact interfaces, morphological and structural deterioration, and unsatisfactory conductivity. Purposeful construction of ball-in-ball structured V2O5 with porous and void architectures wrapped with carbon fibers is expected to overcome the drawbacks, thus bringing the electrochemical performance of V2O5 into full play.In situ construction of ball-in-ball structured porous V2O5 wrapped by intertwined carbon fibers (V2O5@void@V2O5@CFs) is implemented through a simple combined hydrothermal and calcination route. A combination of in/ex situ analytical methods and density functional theoretical calculations are performed to clarify the energy storage mechanism of the material for aqueous ZIBs.The reversible reaction to generate ZnxV2O5·nH2O executes during the zinc ion insertion/extraction procedure in V2O5@void@V2O5@CFs. Benefitting from the synergistic effect of the porous ball-in-ball structure with void space and the wrapped CFs, the material exhibits boosted specific capacity (455 mAh g-1 after 100 cycles and 149 mAh g-1 after 2000 cycles at 4 and 25 A g-1, respectively), cyclic stability, rate ability and energy density (355 Wh kg-1 at 739 W kg-1) when used for aqueous ZIBs due to improved capacitive contribution, fast zinc ion transport dynamics, and enhanced conductivity.