The utilization of lithium (Li) metal is highly desirable, because it is the most attractive anode for high-energy Li batteries, even if there are problems with the unpredictable phenomena of dendritic growth and dead-Li during repeated plating-stripping. So far, the issue of branch-like uneven Li plating has still not been resolved. Recently, using a highly concentrated salt-electrolyte (lithium bis(fluorosulfonyl with a LiNO3additive)) was recognized as the most straightforward approach, although its critical role still remains elusive. Herein, we investigated the overpotential of metallic Li anodes with electrolytes having different salt concentrations and verified the microscopic origins of Li growth, as observed byin situoptical microscopy. We argue that the high ionic conductivity of the electrolyte together with its solid-state interphase effectively suppresses the local potential and concentration gradients, resulting in highly dense dendrite-free Li plating, as supported by in-depth numerical analysis. Our findings provide clear insights that can pave the way to further improvements of the performance of Li metal anodes up to the theoretical limit (3860 mA h g���1).