Interfacial Engineering of Hierarchical VO 2 @Carbon Nanofiber Heterostructures for Ultrahigh Capacity Flexible Zn-Ion Batteries

The advancement of flexible energy storage devices relies critically on the development of a flexible cathode that combines high specific capacity with long-term cycling stability. Here, we report the rational design and fabrication of a freestanding flexible cathode material for Zn-ion batteries (ZIB), denoted as MD-VO 2 @CNF, through electrospinning and thermal conversion of vanadium-based metal–organic framework (V-MOF). The resulting architecture consists of MOF-derived VO 2 nanoparticles uniformly anchored within a conductive carbon nanofiber (CNF) network. This hierarchical structure not only facilitates efficient exposure of active sites and accommodates volume variations during cycling, but also establishes abundant heterointerfaces between VO 2 and CNF. Density functional theory (DFT) calculations reveal that a built-in electric field forms at the VO 2 /CNF interface, which significantly enhances the charge transfer kinetics and strengthens the adsorption of Zn ions. Benefiting from these synergistic effects, the MD-VO 2 @CNF cathode delivers a high specific capacity of 425.8 mAh g –1 at 0.2 A g –1 and exceptional cycling stability, retaining 236 mAh g –1 after 2000 cycles at 5 A g –1 . When integrated into a quasi-solid-state flexible zinc-ion battery, the electrode maintains stable performance under mechanical deformation and achieves a high energy density of 248 Wh kg –1 . This work offers a feasible strategy for designing high-performance flexible energy storage materials and provides fundamental insights into heterointerface engineering for metal oxide-carbon composite systems.