Electrospun MOF/PAN composite separator with superior electrochemical performances for high energy density lithium batteries

A composite separator is prepared with polyacrylonitrile (PAN) and metal-organic framework (MOF) particles by electrospinning, and its physical properties, battery performances and the mechanism of how it improves the performance of high energy density lithium battery are studied. The MOF/PAN separator shows an outstanding thermal stability, an ultra-high electrolyte uptake (794±30%), a high ionic conductivity (2.83 mS cm−1 at 25 °C) and a wide electrochemical window (5.2 V vs. Li+/Li). The Li||separator||Li half-cell can operate stably for 1000 h at 5 mA cm−2. A strong electrostatic interaction between MOF and PF6- in the electrolyte inhibits movement of the anions and enhances the Lithium-ion transference number (tLi+) up to 0.74, which is 64.4% higher than that of PAN separator. After 200 cycles at 0.2 C, the interfacial resistance between separator and electrode only increases from 22.00 to 30.58 Ω. The initial discharge capacity of the NCM811||10% MOF/PAN separator||Li battery system is 166.3 mAh g−1 with 81.3% capacity retention after 250 cycles at 5 C. This research offers an idea to design MOF-based composite separator that makes NCM811||Li battery outstanding in electrochemical stability and high rate performance.