Anchoring anions with metal–organic framework-functionalized separators for advanced lithium batteries

The low Li+ transference number (tLi+), or the relatively small proportion of Li+ conductivity with respect to total ionic conductivity, has been identified as a key drawback of binary electrolytes. The lack of approaches to restrain anion mobility results in the poor cyclability of energy-dense electrodes as the high rate of anion movement induces concentration polarization. Herein, we propose regulating the ion conduction behavior using a nanocomposite separator fabricated via the functionalization of a glass fiber (GF) separator with a metal–organic framework(MOF). The open metal sites in the MOF serve as the anchoring sites for anions, and the resulting tLi+ is increased by 100%. The MOF-functionalized nanocomposite separator with high tLi+ substantially improves the electrochemical performance of a Li metal anode, with an areal capacity exceeding 2 mA h cm−2, and intercalation-type electrodes (LiFePO4 and Li4Ti5O12), with high active material loadings of 45 mg cm−2.