Induction Effect of Fluorine-Grafted Polymer-Based Electrolytes for High-Performance Lithium Metal Batteries

Quasi-solid-state composite electrolytes (QSCEs) show promise for high-performance solid-state batteries, while they still struggle with interfacial stability and cycling performance. Herein, a F-grafted QSCE (F-QSCE) was developed via copolymerizing the F monomers and ionic liquid monomers. The F-QSCE demonstrates better overall performance, such as high ionic conductivity of 1.21 mS cm^-1 at 25 °C, wide electrochemical windows of 5.20 V, and stable cycling stability for Li//Li symmetric cells over 4000 h. This is attributed to the significant electronegativity difference between C and F in the fluorinated chain (‒CF₂‒CF‒CF₃), which causes the electron cloud to shift toward the F atom, surrounding it with a negative charge and producing the inductive effect. Furthermore, the interactions between Li⁺ and F, TFSI^‒, and C are enhanced, reducing ion pair aggregation (Li⁺‒TFSI^‒‒Li⁺) and promoting Li⁺ transport. Besides, ‒CF₂‒CF‒CF₃ decomposes to form LiF preferentially over TFSI^-, resulting in better interfacial stability for F-QSCE. This work provides a pathway to enable the development of high-performance Li metal batteries.