Flexible Metal-Organic Frameworks-Based Carbonized Silk Textile for Long-Life Sodium Storage

Flexible sodium-ion batteries (SIBs) have gained significant attention as a viable option for energy storage, offering enormous potential in wearable flexible electronic devices. CoFe₂O₄ is recognized as a highly attractive anode candidate for SIBs because of its abundant resource availability as well as its high theoretical capacity. Nonetheless, the volume expansion during sodium ions insertion and extraction often leads to structural degradation and decline in capacity. Moreover, its relatively low conductivity limits ion and electron transport, thus affecting its rate performance. This research introduces a novel flexible material composed of biomass-derived carbonized silk textile (CST) and ZIF-67-derived CoFe₂O₄ (ZCFO), synthesized through processes of calcination, acid treatment, and in situ growth. The resulting materials synergistically integrate the high surface area and structural stability of ZIF-67 with the flexibility and conductivity of CST, effectively addressing the capacity degradation induced by volume expansion of CoFe₂O₄ during cycling. Furthermore, it enhances ion and electron transport by shortening the diffusion path, thus improving the overall electrochemical performance. The resulting CST/ZCFO anode shows exceptional stability over extended cycling, maintaining a capacity of 255 mA h g^-1 after 2000 cycles at 2 A g^-1, and demonstrates excellent rate capability, delivering a discharge capacity of 110 mA h g^-1 at 4 A g^-1.