Super Double Interfacial Stabilizer of Ether-Based Electrolyte in Lithium Metal Batteries

Ether-based electrolytes are widely used in lithium metal batteries (LMBs) due to their excellent compatibility with the lithium metal anode (LMA). However, their poor oxidation resistance significantly limits their operational conditions. In this study, we introduce a breakthrough in the design of multifunctional additive—2,4-bis(2-fluoroethoxy)-tetrafluorocyclotriphosphazene (DFEPN)—that overcomes the critical limitations of ether-based electrolytes in LMBs. Leveraging its highly fluorinated molecular structure, DFEPN resolves the long-standing issue associated with the poor oxidation stability in ether-based electrolytes. Remarkably, the fluoroethoxy functionality of DFEPN was found to be compatible with LMA and to regulate the Li⁺ solvation structure through steric effects, demonstrating an innovation path of molecular design for LMBs. On top of that, the fluorinated cyclotriphosphazene ring was recognized to be able to stabilize the cathode interface via a unique dual-protection effect on both electrode–electrolyte interfaces. By incorporating DFEPN into the conventional Dimethoxyethane/1,3-Dioxolane ether-based electrolyte system, the Li/LiFePO₄ full battery exhibits a dramatic leap in performance, i.e., its cycle life surges from severe degradation within merely 75 cycles with only 27.5% capacity retention to 200 cycles with an exceptional 96.4% capacity retention. This study advances the industrial use of LMBs and makes them one step closer to practical implementation.