A Robust Metal-Organic Framework Derived Bioinspired Metal-Polyphenol Network Interface for Enhanced Sodium Storage

The development of flexible anode materials for sodium-ion batteries (SIBs) is crucial for next-generation flexible and wearable electronics. However, conventional flexible current collectors such as carbon cloth and aerogels still suffer from poor interfacial stability and limited mechanical properties. Inspired by biomineralization principles, a bionic metal-phenolic network (MPN) interfacial engineering is introduced to achieve controllable integration of metal-organic framework (MOF) coatings on flexible substrates. A one-step calcination-sulfidation treatment transforms the MOF precusor into uniformly dispersed high-capacity Fe₇S₈ nanoparticles anchored on carbonized silk fabric. The MPN self-assembled through coordination between tannic acid and Fe³⁺, directs uniform growth of MIL-88A, and subsequently converts into an amorphous carbon shell. This carbon interlayer provides strong anchoring of active materials, forms continuous electron-transport pathways, and enhances interfacial stability. The optimized MSMF-2 composite maintains structural integrity after 2000 bending cycles and retains a specific areal capacity of 1.40 mAh cm^-2 after 200 cycles at 0.3 mA cm^-2, while demonstrating 97.3% capacity retention after 1000 cycles at 5 mA cm^-2. Furthermore, solid electrolyte interphase composition and phase-transition mechanisms are systematically investigated, revealing stable interfacial passivation and dual intercalation-conversion storage behavior. This work demonstrates an effective strategy that integrates biomimetic interfacial regulation with MOF-derived active materials.