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-VO2@CNF, through electrospinning and thermal conversion of vanadium-based metal–organic framework (V-MOF). The resulting architecture consists of MOF-derived VO2 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 VO2 and CNF. Density functional theory (DFT) calculations reveal that a built-in electric field forms at the VO2/CNF interface, which significantly enhances the charge transfer kinetics and strengthens the adsorption of Zn ions. Benefiting from these synergistic effects, the MD-VO2@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.