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

Abstract

The low Li⁺ transference number (t_Li⁺), 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 t_Li⁺ is increased by 100%. The MOF-functionalized nanocomposite separator with high t_Li⁺ 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.