Boosting Low‐Temperature Ionic Conductivity in MOF‐Based Solid‐State Electrolytes via Tailored Fluoro‐Ligand Incorporation Into Crystal Frameworks

Abstract The stable operation of solid‐state electrolytes (SSEs) at low temperature is critical for expanding the application of solid‐state lithium batteries (SSLBs) in cold climates. However, there are few relevant literature reports. Herein, a breakthrough is realized to directly address this challenge through tailored fluoro‐ligand incorporation into the crystal framework of MOF‐808. A series of fluorinated MOF‐808 (MOF‐808‐хF, x = 3, 5, 7) are rationally constructed with fluorinated carboxylic acid of different chain lengths through fluorination engineering at the molecular level to precisely modulate the channels surface environment. Specifically, the chemical anchored F groups effectively promote the capture of anions and transport of Li + , while endowing the MOF‐808 with excellent mechanical strength and flexibility, thereby improving the performances of SSEs in operation at low temperature. As a result, the optimized MOF‐808‐5F achieves remarkable ionic conductivity (1.25 × 10 −4 S cm −1 ), high Li + transference number (0.58) and wide electrochemical window (5.4 V) at −40 °C. Furthermore, fluorinated MOF‐808 contributes to LiF solid electrolyte interphase (SEI) formation and effectively inhibits Li dendrites growth, enabling Li|MOF‐808‐5F|Li cell to realize a stable plating/stripping cycling over 1000 h at 0.2 mA cm −2 . Such results provide an insight on the design of electrolytes for SSLBs operating under low temperatures.