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 MgxLi1–2xF 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 MgxLi1–2xF 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 MgxLi1–2xF accelerates the Li-anion dissociation through the electron-deficient site surrounding the hetero-Mg2+ 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 LiFePO4 cathode to operate stably for more than 500 cycles with a retention of 63% compared to its room-temperature capacity.