Rationally Designed Fluorinated Polycation Electrolytes for High-Rate, Dendrite-Free Lithium Metal Batteries

The investigation of high-performance polymer-based electrolytes holds significant importance for advancing the development of next-generation lithium metal batteries (LMBs). In this work, a quasi-solid-state electrolyte (EFA-G) comprising pyrrolidinium type polymeric ionic liquids and fluoropolymers was synthesized through a photoinitiated free radical copolymerization process in the presence of solvate ionic liquids. EFA-G not only exhibited high ionic conductivity (9.87 × 10^-4 S cm^-1) but also had a wide electrochemical stability window (0-5.0 V vs Li⁺/Li). The improvement in Li⁺ transport number (t_Li⁺ = 0.33) of EFA-G was attributed to the enhancement of the Li⁺ migration ability and the hindrance of anion mobility. Due to the shielding effect of the polymeric ionic liquid on the lithium electrode and the formation of a LiF-rich solid electrolyte interphase (SEI), EFA-G supported stable long-term plating/stripping cycling (>1000 h) of lithium symmetric cells. Li/LFP cells assembled with EFA-G at 30 °C exhibited excellent battery performance with a discharge specific capacity of 78.1 mA h g^-1 at 8 C and long cycling life (>600 cycles) with high discharge specific capacity (127.8 mA h g^-1 after 600 cycles). EFA-G also enabled decent performance for high-voltage cathode batteries. This work provides insights into the design of high-performance polymer-based electrolytes for LMBs.