Asymmetrically-Fluorinated Electrolyte Molecule Design for Simultaneous Achieving Good Solvation and High Inertness to Enable Stable Lithium Metal Batteries

Electrolyte molecule engineering, especially symmetrically fluorinated molecules, is recognized as an efficacious approach for solving the insufficient stability of conventional none-fluorinated electrolyte molecules to stabilize the energy-dense Li metal batteries (LMB). However, the weak solvation and low ionic conductivity of symmetrically fluorinated electrolyte molecules, and the formation of low-ionic-conductivity unstable interphase derived from the electrolyte, are the main challenges that limit the applications of symmetrically fluorinated electrolyte for improving LMB performance. Here, an asymmetrically-fluorinated electrolyte molecule design principle is proposed by combining a high-inertness fluorinated structure on one side of the molecule with a solvation-promoting none-fluorinated structure on the other side, successfully integrating the high stability of fluorinated electrolyte and strong solvation/ion-conduction advantages of none-fluorinated electrolyte while remedying their limitations at the same time. The LMB using asymmetrically-fluorinated electrolyte exhibits significantly improved performances of 98.97% Li plating/stripping Coulombic efficiency, decent cathode protection, 240 stable cycles in Li||LiNi0.8Co0.1Mn0.1O2 full-cell under ultralow anode amount, uniform Li deposition morphology and excellent fire-retardancy that overwhelm the similar electrolyte with none-fluorinated or symmetrically-fluorinated molecule structure. The asymmetrically-fluorinated electrolyte molecule design provides a new molecule-level understanding of fluorination degree/position-related structure-property relationship in electrolytes and solves the fluorination-related dilemma for achieving practical high-performance LMB. It proposes a novel asymmetrically-fluorinated electrolyte molecule design that combines the high stability merits of symmetrically-fluorinated and strong-solvation advantages of none-fluorinated electrolytes while addressing their limitations at the same time. The asymmetrically-fluorinated electrolyte exhibits significantly improved performances of 98.97% Li plating/stripping Coulombic efficiency, 240 stable cycles in high-voltage Li||NCM811 full-cell under ultralow anode amount, uniform Li deposition morphology and fire-retardancy.image