Interface-Compatible and High-Cyclability Lithiophilic Lithium–Zinc Alloy Anodes for Garnet-Structured Solid Electrolytes

Zirconia-based lithium garnet solid electrolytes have attracted much attention in solid-state battery research in recent times due to their high lithium ion conductivity, exceptional stability against lithium metal, and broad electrochemical voltage window. However, the application of these electrolytes for realization of all-solid-state lithium metal batteries has been hindered by large electrode–electrolyte interfacial resistance and severe dendrite growth. This is possibly due to the poor wettability of lithium over the garnet solid electrolyte and inhomogeneous lithium deposition across the metallic lithium|electrolyte interface. To deal with this, herein, we fabricated a lithium–zinc alloy electrode as an alternative for lithium metal for application in solid-state batteries. A systematic investigation has been carried out to study the effect of the Li–Zn anode on the wettability and interface kinetics with a Li6.28Al0.24La3Zr2O12 (LLZA) solid electrolyte. The cross-sectional scanning electron microscopy (SEM) image of Li–Zn|LLZA shows an intimate contact, and the impedance spectrum displays an interface resistance as low as 7.5 Ω cm2 for the Li0.95Zn0.05|LLZA|Li0.95Zn0.05 symmetric cell. In addition to low interfacial resistance, the Li0.95Zn0.05|LLZA|Li0.95Zn0.05 cell exhibited a high critical current density of 1.1 mA cm–2. The cycling capability of the Li0.95Zn0.05 alloy anode was demonstrated by cycling the symmetric cell for 2200 h at 0.35 mA cm–2 and 300 h at 0.5 mA cm–2 without short circuiting, realizing a very high cumulative capacity of 930 mAh cm–2 with a LLZA-based solid-state battery. The result presented here paves the way for an interface-compatible anode for the realization of lithium metal batteries based on garnet-structured solid electrolytes.