MIL-53(Fe) anode for lithium-ion batteries with the capacity self-activation effect based on electrochemically induced crystalline-to-amorphization transformation

The relationship between structural changes and electrochemical properties of flexible metal-organic framework materials is a striking phenomenon. We synthesized a highly ordered flexible metal-organic framework called MIL-53(Fe) as an anode for lithium-ion batteries. MIL-53(Fe) 's cyclic performance exhibits capacity self-activation traits. At 100 mA g−1 current density, the specific discharge capacity of 100 cycles is 931.23 mAh g−1, the coulomb efficiency is 98.53%, and the capacity retention rate is 92.60%. The evolution of MIL-53(Fe) throughout the cycle was observed using X-ray diffraction, Raman spectroscopy, and high-resolution transmission electron microscopy. It was discovered that the structure of MIL-53(Fe) experienced an electrochemically induced transition from a crystalline state to an amorphous state. After amorphous conversion, the electrochemical transfer impedance of the material is reduced from 177.2 Ω to 40.6 Ω, the diffusion coefficient of lithium-ion is increased from 3.32 × 10−14 cm2/s to 1.10 × 10−13 cm2/s, and the mass transfer capacity is improved. The results show that MIL-53(Fe) has unique electrochemical properties, and the feasibility of amorphous transition as a mechanism to enhance the electrochemical properties is found.