It is well accepted that a lithiophilic interface can effectively regulate Li deposition behaviors, but the influence of the lithiophilic interface is gradually diminished upon continuous Li deposition that completely isolates Li from the lithiophilic metals. Herein, we perform in-depth studies on the creation of dynamic alloy interfaces upon Li deposition, arising from the exceptionally high diffusion coefficient of Hg in the amalgam solid solution. As a comparison, other metals such as Au, Ag, and Zn have typical diffusion coefficients of 10–20 orders of magnitude lower than that of Hg in the similar solid solution phases. This difference induces compact Li deposition pattern with an amalgam substrate even with a high areal capacity of 55 mAh cm⁻². This finding provides new insight into the rational design of Li anode substrate for the stable cycling of Li metal batteries.