Integrating Activated Inorganic Fluoride Nanocrystals with Polar Polymer for Wide-Temperature Solid Lithium Metal Batteries

The sluggish ionic conduction kinetics and unstable solid electrolyte interface (SEI) inevitably bring about poor low-temperature electrochemical performance of solid-state lithium–metal batteries (SLMBs). In this work, we report a strategy to integrate Mg x Li 1–2 x F with a fluorinated polymer to develop a composite gel electrolyte for wide-temperature SMLBs. The hetero Mg ions induce lattice distortion and electron rearrangement in LiF, and thus, the interaction between the Mg x Li 1–2 x F nanofiller and the polar polymer matrix is awakened to release free F-ions. Consequently, the LiF-rich SEI could be rapidly generated on the Li anode to regulate the interfacial Li plating/stripping. Additionally, the Mg x Li 1–2 x F accelerates the Li-anion dissociation through the electron-deficient site surrounding the hetero-Mg 2+ to achieve low-barrier Li + transport, resulting in an ionic-conductivity of 0.44 mS cm –1 at −20 °C. At −20 °C, the electrolyte enables the LiFePO 4 cathode to operate stably for more than 500 cycles with a retention of 63% compared to its room-temperature capacity.