MIL‐88B‐NH ₂ (Fe)‐Based Fiber‐Reinforced Polymer Electrolytes for Li‐Metal Batteries

The rational design of solid fillers is an effective route to improve the electrochemical performance of solid polymer electrolytes (SPEs). Here we demonstrate that an Fe‐based metal organic framework, MIL‐88B‐NH 2 (Fe), with a fibrous structure, enhances both interfacial stability and ion transport when incorporated into SPEs. MIL‐88B‐NH 2 (Fe) is rich in open metal sites, which increase the ionic conductivity and the Li + transference number. In addition, a stable Fe 3+ /Fe 2+ interfacial layer derived from the MOF metal nodes provides electrostatic shielding, helping to suppress Li dendrite growth and maintain uniform Li deposition. As a result, the designed SPEs achieve an ionic conductivity of 1.1 × 10 −3 S cm −1 at 60°C and a Li + transference number of 0.33, enabling uniform Li + flux and stable cycling. Pouch‐type cells retain 153.7 mAh g −1 after 1500 cycles at 0.5 C and 60°C, highlighting the practical robustness of this electrolyte design.