Fluoride-substituted Li6.4La3Zr1.4Ta0.6O12 with delocalized electron-share accelerates Li+ desolvation kinetics for high-voltage lithium metal batteries

Abstract

Metallic lithium is regarded as the ideal anode material for high-specific-energy batteries. However, the Li(solvents)_x⁺ formation in the liquid-state lithium metal batteries (LMBs) results in sluggish ion transport kinetics and continuous interface deterioration. Herein, an ion-kinetics promoter with delocalized-electron-sharing is designed to reduce the desolvation energy barrier, accelerate interfacial lithium diffusion, and achieve a stable interface. Specifically, the F-substituting Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (named as LLZTO_xF_y) breaks the electron-confined state of the original metal–O (M–O). It induces electron redistribution at the central metal sites, thereby releasing more delocalized electrons. The relationships between charge transfer and ionic desolvation under the delocalized-electron-shared type promoter are comprehensively understood through theoretical calculations and in situ characterization. The F-substitution activates the O–M–F site activity of LLZTO_xF_y, thereby enhancing the binding of solvent CO bonds to these sites, resulting in a high Li⁺ transference number (0.68). Consequently, the lithium–lithium symmetric cell based on LLZTO_0.95F_0.05@PP can stabilize cycling for 1400 h with a lower overpotential (7.3 mV). Meanwhile, the Li|LLZTO_0.95F_0.05@PP|LiCoO₂ full cell can retain a high specific capacity of 88.2% after the 500th cycle at 1.0C under a high voltage of 4.6 V. Therefore, this strategy contributes to achieving long-cycle stability of anodes in LMBs.