In this study, we will present an ionic liquid electrolyte that supports the highly reversible Li metal anode with the cycling coulombic efficiency of ~99.9% at the areal capacity of 5 mAh cm-2. A unique planar growth behavior was observed with operando atomic force microscopy, resulting in an oriented, stack-like lithium deposit. This behavior results from the electrochemically stable solid-electrolyte interphase (SEI) and the stiffened electric double layer near the polarized electrode. The smooth and flat lithium deposit favors lean electrolyte, and the anode-free LiNi_0.8Mn_0.1Co_0.1O₂ || Cu cell has an energy density approaching 450 Wh kg-1. The SEI composition and the controlling factor of the lithium growth in this electrolyte will be discussed in detail.