Boosting ultra-fast charging in lithium metal batteries through enhanced solvent-anion interaction via conjugation effect

In pursuit of higher energy density, adopting a lithium metal anode holds promise for the evolving battery technology. Nevertheless, practical obstacles persist, including explosion hazards, restricted fast charging (>5C), and lithium metal compatibility issues. To tackle these challenges, we devised a non-flammable deep eutectic electrolyte (DEE) comprising lithium bisfluorosulfonimide (LiFSI) and prop-1-ene-1,3-sultone (PES). This DEE demonstrates exceptional attributes, including near 98.76% Coulombic efficiency and a high ionic conductivity of 1.96 mS cm(-1). We found that the electron-absorbing effect of the double-bonded structure enhances the interactions between PES and FSI-, releasing more free lithium ions and boosting the Li+ transference number of 0.78. Our engineered DEE fosters the formation of a robust organic-inorganic gradient solid electrolyte interphase (SEI) with a surface layer rich in organic species and an inner layer rich in inorganic species. The high Li+ transfer number and stable SEI together enable ultra-fast charging and sustained cycling, with 81.32% capacity retention after 1000 cycles at 10C in the LiFePO4 & Vert;DEE & Vert;Li battery. Meanwhile, the mechanistic reasons behind fast charging performance are elaborated by theoretical calculations, and its practical applicability is underscored through successful implementation in pouch cells with high loading and 30 mu m of Li metal.