Wet Chemical Method ZnF₂ Interlayer for High Critical Current Density Lithium Metal Batteries Utilizing Ba and Ta–Doped Li₇La₃Zr₂O₁₂ Garnet Solid Electrolyte

Abstract Li metal batteries with garnet‐type solid electrolytes have the potential to increase specific energy and power densities of current Li‐ion batteries. Li metal batteries have been hampered by the poor wettability of solid electrolyte with elemental lithium. Here, to resolve the solid garnet electrolyte/Li interface issue, a scalable, cost‐effective, and efficient surfactant‐assisted wet‐chemical strategy is developed. A ZnF 2 interlayer coating is applied on Ba and Ta ‐co‐doped Li 7 La 2.75 Ba 0.25 Zr 1.75 Ta 0.25 O 12 that formed LiF and Li‐Zn alloy upon contact with molten Li. Conformal contact applying a homogenous surfactant‐assisted ZnF 2 coating reduced the interfacial resistance from 87 to 15.5 Ω cm 2 which enhanced critical current density to a record high value of 5 mA cm −2 at room temperature. Dense and Li 2 CO 3 free garnet solid electrolyte assisted in achieving long‐term stability for 1000 cycles at 1 mA cm −2 . Interface stabilized Li/ZnF 2 ‐ solid electrolyte/liquid electrolyte/LiFePO 4 cell displayed a 90% capacity retention over 800 cycles at 0.2 C, with Coulombic efficiency of 99% as well as excellent cycle stability at 1 C, with ≈91% of capacity retention for 500 cycles. Using a new design principle for Li anode interfaces, next‐generation power‐intensive and stable solid‐state Li metal batteries can be developed.