Wet chemical method ZnF₂ interlayer for high critical current density lithium metal batteries utilizing Ba and Ta-doped Li₇LA₃Zr₂O₁₂ garnet solid electrolyte

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 ZnF₂ interlayer coating is applied on Ba and Ta -co-doped Li₇La_2.75Ba_0.25Zr_1.75Ta_0.25O₁₂ that formed LiF and Li-Zn alloy upon contact with molten Li. Conformal contact applying a homogenous surfactant-assisted ZnF₂ coating reduced the interfacial resistance from 87 to 15.5 Ω cm² which enhanced critical current density to a record high value of 5 mA cm⁻² at room temperature. Dense and Li₂CO₃ free garnet solid electrolyte assisted in achieving long-term stability for 1000 cycles at 1 mA cm⁻². Interface stabilized Li/ZnF₂- solid electrolyte/liquid electrolyte/LiFePO₄ 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.