Nano‐Interfacial Supramolecular Adhesion of Metal–Organic Framework‐Based Separator Enables High‐Safety and Wide‐Temperature‐Range Lithium Batteries

Polyolefin separators are the most commonly used separators for lithium batteries; however, they tend to shrink when heated, and their Li⁺ transference number (t _Li ⁺) is low. Metal-organic frameworks (MOFs) are expected to solve the above problems due to their high thermal stability, abundant pore structure, and open metal sites. However, it is difficult to prepare high-porosity MOF-based membranes by conventional membrane preparation methods. In this study, a high-porosity free-standing MOF-based safety separator, denoted the BCM separator, is prepared through a nano-interfacial supramolecular adhesion strategy. The BCM separator has a large specific surface area (450.22 m² g^-1) and porosity (62.0%), a high electrolyte uptake (475 wt%), and can maintain its morphology at 200 °C. The ionic conductivity and t _Li ⁺ of the BCM separator are 1.97 and 0.72 mS cm^-1, respectively. Li//LiFePO₄ cells with BCM separators have a capacity retention rate of 95.07% after 1100 cycles at 5 C, a stable high-temperature cycling performance of 300 cycles at 80 °C, and good capacity retention at -40 °C. Li//NCM811 cells with BCM separators exhibit significantly improved rate performance and cycling performance. Pouch cells with BCM separators can work at 120 °C and have good safety at high temperature.